LITHOS-'stone' GRAPHO-'to write’ Method of PRINTING by using LITHOGRAPHIC STONE(LIMESTONE) METAL PLATE IMAGE (ON WAX OR OILY SUBSTANCE) Transfer MEDIUM (LITHOGRAPHIC STONE OR METAL PLATE) Printed PRINTED SHEET IMAGE (POLYMER) HYDROPHILIC -ACCEPT WATER -REJECTS.
Download ReportTranscript LITHOS-'stone' GRAPHO-'to write’ Method of PRINTING by using LITHOGRAPHIC STONE(LIMESTONE) METAL PLATE IMAGE (ON WAX OR OILY SUBSTANCE) Transfer MEDIUM (LITHOGRAPHIC STONE OR METAL PLATE) Printed PRINTED SHEET IMAGE (POLYMER) HYDROPHILIC -ACCEPT WATER -REJECTS.
Slide 1
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 2
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 3
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 4
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 5
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 6
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 7
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 8
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 9
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 10
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 11
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 12
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 13
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 14
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 15
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 16
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 17
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 18
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 19
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 20
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 21
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 22
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 23
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 24
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 25
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 26
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 27
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 28
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 29
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 30
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 31
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 32
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 33
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 34
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 35
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 36
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 37
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 38
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 39
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 2
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 3
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 4
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 5
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 6
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 7
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 8
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 9
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 10
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 11
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 12
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 13
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 14
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 15
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 16
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 17
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 18
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 19
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 20
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 21
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 22
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 23
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 24
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 25
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 26
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 27
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 28
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 29
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 30
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 31
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 32
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 33
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 34
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 35
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 36
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 37
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 38
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.
Slide 39
LITHOS-'stone'
GRAPHO-'to write’
Method of PRINTING by using
LITHOGRAPHIC STONE(LIMESTONE)
METAL PLATE
IMAGE (ON WAX OR OILY SUBSTANCE)
Transfer
MEDIUM (LITHOGRAPHIC STONE OR
METAL PLATE)
Printed
PRINTED SHEET
IMAGE (POLYMER)
HYDROPHILIC
-ACCEPT WATER
-REJECTS INK
MEDIUM
(ALUMINIUM PLATE)
PRINTED SHEET
HYDROPHOBIC
-ACCEPT INK
-REJECTS WATER
FLEXIBLE SHEET (RUBBER)
PRINTED SHEET
It uses chemical processes to create an image.
Parts of an image:
Positive part
Negative image
- Hydrophobic “water hating” substance.
- Hydrophilic "water loving“ substance.
When the plate is introduced to printing ink and water mixture, the
ink will adhere to the positive image and the water will clean the
negative image.
This allows a flat print plate to be used, enabling much longer and
more detailed print runs.
It refers to PHOTOLITHOGRAPHY AND DIRECT BEAM LITHOGRAPHY
A microfabrication technique used to make
◦ Integrated circuits
◦ MEMS (microelectromechanical systems).
Cleaning
Preparation
BASIC PROCEDURE
Photoresist application
Exposure and developing
Etching
Photoresist removal
1.CLEANING
◦ To remove Organic or Inorganic contaminations present on the wafer surface
◦ Usually by Wet chemical treatment
2.PREPARATION
◦ Heat treatment to remove moisture from wafer.
◦ Adhesion promoters added to promote adhesion of photoresist on wafer.
EX: ADHESION PROMOTER – hexamethyldisilazane (HMDS)
◦ Silicon dioxide layer on the wafer reacts with the agent to form Methylated Siliconhydroxide, a highly water repellent layer, to protect from aqueous developers.
3.Photoresist application
The wafer is covered with photo resist by spin coating.
STEPS
◦ A viscous, liquid solution of photo resist is dispensed onto the
wafer, and the wafer is spun rapidly to produce a uniformly thick
layer.
Speed
- 1200 -4800 rpm
Time
- 30-60 seconds
Layer Thickness - 0.5-2.5 micrometres
◦ Prebaked :The photo resist-coated wafer is then prebaked to drive
off excess photoresist solvent
Temp - 90 to 100 °C
Time
- 30 to 60 seconds
4. Exposure and developing
Photoresist is exposed to a pattern of intense light (Through Mask).
Photolithography typically uses ultraviolet light.
A pattern from the mask is copied on the photoresist by the light.
Photoresist is then developed in developer depending upon the type of
photoresist used.
Exposer of light makes bonds of positive photoresist weaker and that of the
negative photoresist stronger, where it falls on it.
◦ Mask
An opaque plate with holes or transparencies that allow light to shine through in
a defined pattern.
Consists of transparent fused silica blanks covered with a pattern defined with a
chrome metal absorbing film.
MASK
(WITH PATTERN)
PHOTORESIST
(AFTER DEVELOPMENT)
◦ Photoresist
Positive photoresist
Negative photoresist
◦ Developer
- Soluble in the basic developer when exposed
- Insoluble in the (organic) developer.
- A solution used to remove unwanted photoresist.
5.Etching
A liquid ("wet") or plasma ("dry") chemical agent removes the
uppermost layer of the substrate in the areas that are not protected
by photoresist.
6. Photoresist removal
After a photoresist is no longer needed, it must be removed from
the substrate.
Liquid “resist stripper“ : It chemically alters the resist so that it no
longer adheres to the substrate.
Also known as Maskless lithography.
The radiation is not transmitted through, a photomask, instead, the
radiation is focused to a narrow beam. The beam is then used to
directly write the image into the photoresist.
Other procedure are same as in photolithography.
Different types of direct beam lithography:
◦ Electron beam lithography
◦ Optical (direct laser) lithography
◦ Focused ion beam
◦ Probe tip contact
Contains one or more monolayers of an organic material.
Deposited from the surface of a liquid onto a solid by immersing the solid
substrate into the liquid.
A monolayer is adsorbed homogeneously with each immersion step, thus
films with very accurate thickness can be formed.
The thickness is accurate because the thickness of each monolayer is
known.
The monolayers are assembled vertically and are usually composed of
AMPHIPHILIC MOLECULES.
PHYSICAL INSIGHT
◦ LB films are formed when amphiphilic molecules (surfactants) interact with
air at an air-water interface.
◦ Surfactants are molecules
SURFACTANTS
(SURFACE ACTING AGENT)
HYDROPHILIC
HEAD
HYDROPHOBIC
TAIL
◦ When surfactant concentration is less than critical micellar concentration
(CMC), the surfactant molecules arrange themselves as shown in Figure
◦ Hydrophobic tails favoured the tail-air interaction
Hydrophilic head favoured the head-water interaction
◦ The overall effect is reduction in the surface energy (or surface tension of
water).
LB films
Micelle
CMC: The concentration of surfactants above which
micelles are spontaneously formed .
Micelle: An aggregate of surfactant molecules
dispersed in a liquid colloids
Langmuir-Blodgett trough
It is a laboratory apparatus
Used to compress monolayers of molecules on the surface of a given
subphase (usually water) and measures surface phenomena due to this
compression.
It can also be used to deposit single or multiple monolayers on a solid
substrate.
1. Amphiphilc monolayer
2. Liquid subphase
3. LB Trough
4. Solid substrate
5. Dipping mechanism
6. Wilhelmy Plate
7. Electrobalance
8. Barrier
9. Barrier Mechanism
10. Vibration reduction system
11. Clean room enclosure
DEPOSITION
MONOLAYER
COMPRESSION
It is important to maintain constant surface pressure during deposition in
order to obtain uniform LB films.
Measurement of surface pressure can be done by means of a
Wilhelmy plate (or Langmuir balance).
The surface tension calculated by the following equation:
Wilhelmy plate
l = (2w + 2d)
w = width
d = thickness
Defined as
“ spontaneous and reversible organization of molecular units into ordered structures
by non-covalent interactions (local interaction) without external direction ”
For self assembly subunits need certain properties like:
◦ Charge, polarizability, magnetic dipole, specific surface properties.
Self-assembly can be classified as:
◦ Static self-assembly system:
It involves system that are at local equilibrium and do not dissipate energy.
Formation of structure needs energy but once it is formed, it becomes stable.
◦ Dynamic self-assembly structures :
The interactions responsible for the formation of patterns between components
only occur if the system is dissipating energy.
Example:
Formation of Molecular crystals, colloids, lipid bilayers, and self-assembled
monolayers.
There are at least three distinctive features of SA
Order
It must have a higher order than the isolated components.
Interactions
Aspect of SA is the key role of weak interactions (e.g. Van
der Waals, capillary, π − π, hydrogen bonds) with respect
to more "traditional" covalent, ionic or metallic bonds.
Building blocks
The building blocks are not only atoms and molecules, but
span a wide range of nano and mesoscopic structures,
with different chemical compositions, shapes and
functionalities.
It has three main properties—
Weak interactions:
◦ Self-assembling molecules adopt a structure, finding the best combination of
interactions between subunits but not forming covalent bonds between them.
Thermodynamic stability:
◦ For SA to take place without intervention of external forces, the process must lead
to a lower Gibbs free energy, thus self-assembled structures are thermodynamically
more stable than the single, unassembled components.
Reversibility
◦ The weak nature of interactions is responsible for the flexibility of the architecture
and allows for rearrangements of the structure in the direction determined by
thermodynamics.
◦ If fluctuations bring the thermodynamic variables back to the starting condition,
this leads to reversibility
SELF ORGANIZATION
Non-equilibrium
process
SELF ASSEMBLY
Equilibrium process
Components changed
No. of components
comparatively less
Components remain
unchanged
No. of components
very large
An organized layer of amphiphilic molecules, shows a special affinity
for a substrate.
Formed by the chemisorption of hydrophilic “head groups” onto a
substrate followed by a slow two-dimensional organization of
hydrophobic “tail groups”.
The monolayer packs tightly due to van der walls interaction,
thereby reducing its own free energy and are more stable than the
physisorbed bonds of Langmuir–Blodgett films.
A. Locally attract
It involves locally depositing self-assembled monolayers on the surface only where the
nanostructure will later be located.
The major techniques are:
1. Micro-contact printing
Micro-contact printing is analogous to printing ink with a rubber stamp.
The SAM molecules are inked onto an pre-shaped elastomeric stamp with a
solvent and transferred to the substrate surface by stamping.
The transfer of the SAMs is a complex diffusion process that depends on the type
of molecule, concentration, duration of contact, and pressure applied.
Typical stamps use PDMS (Polydimethylsiloxane)
Figure 1
"Inking" a stamp. PDMS stamp with pattern is placed in
Ethanol and ODT (octadecanethiol) solution
Figure 2
ODT from the solution settles down onto the PDMS stamp.
Stamp now has ODT attached to it which acts as the ink.
Figure 3
The PDMS stamp with the ODT is placed on the
gold substrate. When the stamp is removed,
the ODT in contact with the gold stays stuck to
the gold. Thus the pattern from the stamp is
transferred to the gold via the ODT "ink
2. DIP PEN LITHOGRAPHY
◦ It uses an atomic force microscope to transfer molecules on the tip to a substrate.
◦ Tip (Dipped into a reservoir with an ink and molecules)
EVAPORATION
◦ Tip (only with the desired molecules )
◦ Surface
◦ Diffusion of molecules from tip to surface due resulting due to a water meniscus
forms between the tip and the surface.
Meniscus :The curved upper surface of a non-turbulent liquid in a vertical tube
Tip radii: ~10 nm
B. Locally remove
It begins with covering the entire surface with a SAM. Then individual SAM molecules
are removed from locations where the deposition of nanostructures is not desired.
The major techniques that use this strategy are:
1. Scanning tunneling microscope (STM)
a. Remove SAM molecules mechanically by dragging the tip across the substrate
surface.
b. Degrade the SAM molecules by shooting them with an electron beam.
STM
2. Atomic force microscope (AFM)
Removal of SAM molecules by this method is called shaving.
◦ AFM tip is dragged along the surface mechanically removing the molecules.
◦ When the tip is brought into proximity of a sample surface, forces between the tip
and the sample lead to a deflection of the cantilever according to Hooke's law.
F=Restoring force
x=displacement
k=force constant
It can also remove SAM molecules by local oxidation nanolithography.
3. Ultraviolet irradiation
◦ UV light is projected onto the surface with a SAM through a pattern of apperatures
in a chromium film. This leads to photo oxidation of the SAM molecules. These can
then be washed away in a polar solvent.
◦ Exposure time :15-20 minutes.
Control of wetting and adhesion
Chemical resistance
Bio compatibility
Sensitization
Molecular recognition for sensors and nano
fabrication.