Transcript Electric Field Aligned CVD Growth of Single Walled Carbon

The Tools of Nanotechnology
Universeum
28th March 2006
The Science Behind Nanotechnology
The Tools to Make and Analyse Nanostructures
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Matter consists of atoms
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Each atom contains positively charged protons and an
equal number of negatively charged electrons (protons
are much heavier than electrons)
Charged particles interact via the Coulomb Interaction
Q1Q2
F 2
r
Opposite charges: negative (attractive force);
Like charges: positive (repulsive force)
If the number of protons is different from the number
of electrons we have an ion
But: atoms are not really like miniature solar systems
and electrons can behave like particles or like waves!
Classical Mechanics needs to be replaced by Quantum
Mechanics at the atomic level
How big is an atom?
0.1 – 0.2 nm
On the atomic / nm scale energy and charge cannot be added
continuously to matter, but can only be added in small pieces.
Quanta for energy, electrons for charge.
The charge of an ion is quantised – it is not possible to add or
subtract less than one electron.
(Money is quantised with the fundamental quantum of 50 ore)
Bulk
semiconductor
Characteristic
emission from
atoms - e.g.
Yellow Na lines
Manipulate the
energy levels
by changing
the size of the
particle
Energy levels too
close to observe
quantisation within
a band
Gold and Silver Particles:
Plasmon Resonance
Size-dependent frequency of
collective electron oscillations
Semiconductor Nanoparticles:
Fluorescence
Molecules are formed when atoms are brought
together in a fixed structure.
All chemical bonds are caused by interactions between
the electrons of the atoms.
The electrons are responsible for the chemical
properties of atoms and molecules.
Electron interactions are key to nanotechnology. They
combine atoms into molecules or nanoparticles. The
bonds themselves can act as mechanical devices such
as hinges or bearings.
Molecular switch –
controlled by electric
field direction or light or
chemical environment..
On: conducting
4,4'-Di(ethinylphenyl)-2'nitro-1-benzothiolate
Off: insulating
Different kinds of material important for nanotechnology:
Metals: Electrons are ”free” to move beween the metal
atoms in the bulk. Good conductors of electricity. Free
elecrons also scatter light efficiently.
Bulk metals follow Ohm’s law. V = IR.
This is not necessarily the case on the nanoscale.
Polymers or Macromolecules: usually based on carbon.
Single molecules formed of repeating patterns in a
chain. Generally they do not conduct electricity (but
some special ones do and can be used e.g. as
molecular wires or to make electronic devices, NP in
chemistry 2000).
Biopolymers: DNA, proteins, polysaccharides
Ceramics:
Composed of different kinds of atoms (usually containing
oxygen). Electrons are localised so do not conduct
electricity.
Carbon Nanostructures:
Pure carbon materials, localised electrons produce a
strong and stable structure. Delocalised electrons
responsible for electronic properties.
Each carbon atom has 4
electrons that can interact with
neighbouring atoms: for
nanotubes, fullerenes and
graphite, 3 electrons form
localised strong bonds and 1
electron is delocalised
Molecular Recognition: ”Self-Assembly”
Molecules have shapes and charges. Often the electrons
are distributed unevenly.
Because Coulomb’s law tells us that positive charges are
attracted to negative charges, molecules can interact with
one another by electrical (Coulomb) forces.
The ability of one
molecule to attract and
bind specifically to
another is often referred
to as molecular
recognition.
Biological Systems make great use of molecular
recognition e.g. Smell or taste detection.
Biomimetics: copying biology (e,g. Making sensors
based on moelcular recognition, artificially producing
surfaces with the same behaviour as lotus leaves,.....)
Related to molecular recognition is making use of
the intermolecular interactions to induce selfassembly of interesting nanosystems
Large biological molecules can recognise one another and,
in so doing, build the cells by which higher biological
organisms are structured.
Molecular recognition combined
with self-assembly is a key
feature of Nanotechnology.
Because much of
nanotechnology depends on
building from the bottom up,
making molecules that can
organise themselves on their
own or with a supporting surface
is a key strategy for
manufacturing nanostructures.
To manipulate material on the atomic
level it helps to ”see” the atoms
High resolution electron microscopy has made great
advances and it is now possible to see individual atoms,
even as smal as Li (1Å resolution).
High resolution Transmission Electron Microscope
Transmission electron microscopes
use high electric voltages — as
much as 400,000 volts — to
accelerate a beam of electrons
within a vacuum chamber. The beam
is then aimed at a thin slice of the
material under study. After the
powerful beam of electrons passes
through the sample, it is focused
and projected onto either a monitor
or photographic film to provide an
image of the structure.
Transmission electron microscopes
can provide magnification as much
as 1.5 million times. Since the
electron beam must pass through it,
preparation of the sample is critical.
Scanning Tunnel Microscope
Binnig and Röhrer, NP 1986
Possible to ”see” and
MANIPULATE individual
atoms
STM scan of graphite
STM scans of carbon
nanotubes
Atomic Force Microscope
Principle of AFM based data storage system
IBM’s Millipede
MILLIPEDE- 2D array of
cantilevers
Actual image of data bits
written on PMMA
Image from:
http://www.research.ibm.com/journal/rd/443/vetti1.gif
Magnetic
Force
Microscopy
MFM picture of the bits
of a hard disk
(30µm x 30 µm)
STM: Electron waves on a CNT Peapod
STM studies of the
electronic structure of
carbon nanotube ”peapods”
Captured molecules
influence the electronic
structure and behaviour
without changing the atomic
structure of the surrounding
carbon cylinder
D. Hornbaker and A. Yazdani
How to make ”top down” nanostructures
Llithography in clean room conditions (MC2 Chalmers)
• Chalmers logo made
by electron beam
lithography.
• Gold on a silicon
surface.
• 8 mm in diameter and
the narrowest
linewidth is 30 nm.
• About 100 of these
may fit in on the cross
section of a hair.
Bengt Nilsson SnL (Swedish nanometer laboratory)
”Large” structures can be made with photolithography.
Small structures with electron beam lithography but principle is
the same
Mask
S1813
LOL2000
Expose the desired structure to radiation using a mask
Develop the Resist
Irradiation damages
the photoresist polymer
The damaged part can be
removed with chemicals
LOL
Evaporate a thin layer of metal onto the structure
Dissolve the LOL layer
Photolithography for the large structures. E-beam
lithography for the small electrodes
Lithography is a complicated and time-consuming but
very powerful technique for making nano structures in a
controlled way
But very expensive!
For commercial production of nanostructures, we need
something quicker and much less expensive:
Nano-imprint Lithography: back to the SPM
Top down nanostructure processing at Chalmers MC Lab.
Access to lithography facilities, SPM and electron microscopes
Some links:
Slightly more scientifically advanced book:
”Nanotechnology: basic science and emerging
technologies” Wilson et al. (Chapman & Hall 2004)
Web Links:
Exploring the nanworld with LEGO:
http://mrsec.wisc.edu/Edetc/LEGO/index.html
Self-Assembly:
http://www.math.udel.edu/MECLAB/Projects/SelfAssembly/
selfassembly1.htm
General: http://www.nano.gov/html/edu/eduteach.html
http://www.mrsec.wisc.edu/Edetc/index.html
http://www.sciencemuseum.org.uk/antenna/nano/