Transcript Slide 1

Part 3ii
Electron Beam Lithography
SAMs
Specific Chemistry
Learning Objectives
After completing PART 3ii of this course you should have an understanding of, and be
able to demonstrate, the following terms, ideas and methods.
(i)
The surface chemistry is induced by back scattered and secondary
electrons,
(ii)
Appreciate how the surface chemistry is probed by various spectroscopic
techniques,
(iii) Appreciate how the modified surfaces can be utilised as platforms for
building the structures into the third dimension, and
(iv) Appreciate the various chemistries that are initiated by the electron beam.
There’s a nuclear scientist, a genetic engineer and a
nanotechnologist all being held at the barrel of a gun by a crazy man.
The captor says he’ll shoot all of them unless they can convince him
they are doing something good for the world.
There’s a nuclear scientist, a genetic engineer and a
nanotechnologist all being held at the barrel of a gun by a crazy man.
The captor says he’ll shoot all of them unless they can convince him
they are doing something good for the world.
The nuclear scientist tries first, explaining that nuclear power is
“clean, cheap, and will solve climate change.” Unconvinced, his
captor shoots him dead and turns next to the nanotechnologist to
plead his case.
There’s a nuclear scientist, a genetic engineer and a
nanotechnologist all being held at the barrel of a gun by a crazy man.
The captor says he’ll shoot all of them unless they can convince him
they are doing something good for the world.
The nuclear scientist tries first, explaining that nuclear power is
“clean, cheap, and will solve climate change.” Unconvinced, his
captor shoots him dead and turns next to the nanotechnologist to
plead his case.
Before he can say a word however, the genetic engineer intervenes.
“No!” pleads the genetic engineer “please shoot me first – I’d rather
die than hear yet another lecture on why nanotechnology is going to
save the world!”
Patterning: Direct-Beam Writing
The e-beam initiates specific chemical reactions in the SAM.
Literally the electrons are a reagent!
e
b
e
a
m
A single
molecular
monolayer
…But it is not the incident beam electrons, but the secondary and back scattered
electrons, which are much lower in energy and are able to enter a LUMO of the SAM
forming molecules(10-25 eV), and induce a chemical reaction….IMPORTANT POINT
Converting an
Aromatic Nitro Group
to an
Aromatic Amine
Ar-NO2 to Ar-NH2
e-beam
W. Eck, V. Stadler, W. Geyer, M. Zharnikov, A.
Gölzhäuser, M. Grunze,
Adv. Mater. 2000, 12, 805.
J. Vac. Sci. Technol. B 2001 19, 2732.
N O2 N O2 N O2 N O2 N O2
S
S
S
S
S
Au
N O2 N H2 N H2 N O2 N O2
AFM micrograph in frictional
mode.
S
Au
S
S
S
S
R1
R1
O
O
N O2 N O2
N O2H N H N
Excellent system as chemical reactivity
between nitro and amino group is different.
S
Au
S
S
S
S
Characterising
the Conversion
Surface FT-IR
N=O symmetric
stretching mode
mC/cm2
(a) 0
(b) 10 000
(c) 15 000
(d) 27 000
(e) 35 000
(f) Chemically
Reduced
SAMs on Gold no good for electronic applications….
SAM on Si/SiO2
Film Formation
Immerse Si/SiO2 into 5 mM/anhy. THF
under Ar
(Sonication at 25°C)
Reaction times: 2 hours
NPPTMS
O2N
O
Si(OMe) 3
NO 2 NO 2 NO 2 NO 2 NO 2 NO 2
Sonicate twice in fresh THF for 5 min
Rinse intensively with CHCl3, EtOH
and UHP H2O
Dry under Ar
Film Characterisation:
1.1 nm
O
O
O
O
O
O
Contact Angle (surface type)
AFM (roughness)
O Si O Si O Si O Si O Si O Si O
O
O
O
O
O
O
Si
Si
Si
Si
Si
Si
Langmuir 2004, 20, 3766-3768
Elipsometry (thickness)
XPS (elemental composition)
XPS Chemical Modification
SAM Thickness (ellipsometry) = 1.2  0.2 nm
Calculated = 1.1 nm
NH 2 (399.6 eV)
Intensity / arbitrary units
NO 2 ( 405.6 eV)
(e) 447 min
(d) 273 min
(c) 163 min
(b) 97 min
(a) 3 min
409
404
Binding energy / eV
399
Secondary back scattered electrons initiate the chemistry
394
Confirming the Chemical Transformation: NO2 to NH2
NH2
• Immersion
of
the
irradiated surface in a
10% TFAA solution in
dry THF overnight
CF3
C
O
NH
O
O
Si
O
Si
O
O
O
Si/SiO2
Si/SiO2
• E-beam
NO2
O
Si
• Immersion
of
the
irradiated surface in a
10% TFAA solution in
dry THF overnight
Intensity (arbitrary units)
F (1s)
XPS
O
O
700
Si/SiO2
695
690
685
Binding energy (eV)
680
Patterning: Direct-Beam Writing
P. Mendes, S. Jacke, Y. Chen, S.D.
Evans, K. Kritchley, K. Nikitin, R. E.
Palmer, D. Fitzmaurice, J.A. Preece,
Langmuir, 2004, 20, 3766-3768.
SEM Image
e
NO2
b
e
a
m
primary beam energy
= 5 and 6 keV
doses between
= 25 and 300 µCcm-2
NH2
5 mm
Self-Assembling into the Third Dimension
NH2
NO2
Background:
How
to
Increase Differentiation?
HO
CO2
CO2
CO2
Citrate
Stabiliser
- -
-
-
-
-
-
-
16 nm
diameter
-
-
-
-
-
NH 2
-
NH
NH32
-
-
NH 2
NH 2
pH-Dependent Adsorption of Gold
Nanoparticles on AminothiophenolModified Gold Substrates
S
S
S
S
Tao Zhu, Xiaoyi Fu, Tao Mu, Jian
Wang, Zhongfan Liu
Langmuir 1999, 15, 5197-5199
Adsorption
of
Particles to eBeam Patterned
Surface
at
pH 4.5
AFM Images
3.9µm
2.6µm
570nm
180nm
And Our Smallest Result to Date!
90 nm
2.9µm
510nm
As a pre-med student at UW Madison, I had to take a difficult
class in physics. One day our professor was discussing
nanotechnology, complicated concept. A student in the back of
Sterling rudely interrupted to ask,
"Why do we have to learn this stuff?"
"To save lives." The professor responded quickly and continued
the lecture.
A few minutes later, the same student spoke up again
As a pre-med student at UW Madison, I had to take a difficult
class in physics. One day our professor was discussing
nanotechnology, complicated concept. A student in the back of
Sterling rudely interrupted to ask,
"Why do we have to learn this stuff?"
"To save lives." The professor responded quickly and continued
the lecture.
A few minutes later, the same student spoke up again
"So how does physics save lives?" he persisted.
As a pre-med student at UW Madison, I had to take a difficult
class in physics. One day our professor was discussing
nanotechnology, complicated concept. A student in the back of
Sterling rudely interrupted to ask,
"Why do we have to learn this stuff?"
"To save lives." The professor responded quickly and continued
the lecture.
A few minutes later, the same student spoke up again
"So how does physics save lives?" he persisted.
"It usually keeps the idiots like you out of medical school,"
replied the professor.
Initiating Radical Chemistry
And Surface Polymer
Chemistry
Generating Radicals
C-Br bond
homolytically
cleaved induced
by e-beam to
generate
radicals
ATRP = Atom Transfer Radical Polymerisation
Monomers = styrene and methyl methacrylate
Langmuir, 2003, 19, 4519
Evidence for Loss of Br
XPS Br (3d)
SAM before irradiation
SAM irradiation (2 mins)
SAM irradiation (4 mins)
SAM irradiation (6 mins)
Evidence for Polymerisation
AFM
AFM Line Section
Etched
with HF
30 nm step
height
5 mm
30 nm equates to ~
50 monomer units
Cutting a Disulfide Bond
Cleaving a R-S-S-R Bond
e
The RS-SR bond is weak 55kcal mol-1
The RS-SR can be electrochemically
reductively cleaved.
- SPh
H
H
H
H
RS- and RS. are relatively stable
entities, thus hypothesis is that
secondary and back scatteresd
electrons from an incident e-beam
could reduce the disulfide bond.
Thus, after cleavage the initially
unreactive surface would be reactive
by expressing a thiol (RSH) moiety.
Langmuir, 2003, 19, 9748
Writing with the e-Beam: Making Nanotrenches
Loss of the S-Ph moiety to the vacuum
Chemically Backfilling the Trench
AFM After Irradiation
AFM After Irradiation
N-(1-pyrene)maleimide
Trenches become Humps
‘Welding’ Gold
Nanoparticles Together!
Writing Gold Nanowires: Negative Tone E-Beam Resist
e
e
Film of Au
Gold nanoparticles
eee
nanoparticles
fuse together, and
The electron beam
e
e
e
passivated
organic evaporates
e
e
initiates
cleavage
of
ee
with an
in UHV.
Au-passivant
organic ligand e e
interaction.
e
The
nanopartices
are
rinsed
away with an
organic solvent, leaving
the gold nanowire.
J. Phys.: Condens. Matter, 2003, 15, S3047-S3063.
The Organic Passivant
S
Organic passivant stops the
nanoparticles aggregating
S
S
S
S
GoldThiolate
Bond
But
E-beam
degrades
the
passivant,
leaving
carbonaceous residue in the
gold.
Not
conductor.
exactly
a
good
A New Passivant for Gold Nanoparticles
Alkyl Thiols
Dialkyl Sulfides
SAM on planar gold
formed from alkylthiols
SAM on planar gold
formed from dialkylsulfides
R.G. Nuzzo, F.A. Fusco, D.L. Allara
J. Am. Chem. Soc., 1987, 109, 2358
E.B. Troughton, C.D. Bain, G.M. Whitesides
Langmuir, 1988, 4, 365
S
S
S
S
Au-S Bond = 120 kJ mol-1
S
S
S
S
Au-S Bond = 60 kJ mol-1
D.J. Lavrich, S.M. Wetterer, S.L. Bernasek, G.J. Scoles, J. Phys. Chem. B 1998, 102, 3456
Synthesis of Nanoparticles
N(Oct)4Br
(PhMe)
45 minutes
HAuCl4
(H2O)
Passivant
N(Oct)4AuCl4
HBr
Passivant
NaBH4 In water (30 mL)
Nanoparticle
Solution
SH
S
C10SH
C10SC10
1.
Separate PhMe layer
2.
Precipitation (MeCN)
3.
Centrifugation
N(Oct)4AuCl4
Brust, M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; Whyman, R.
J. Chem. Soc., Chem. Commun. 1994, 801.
Inoue, K.; Shinkai, S.; Huskens, J.;
Reinhoudt, D.
J. Mater. Chem. 2001, 11, 1919.
TEM Characterisation
Nanoparticles assembled on graphite from solution (CDCl3) drop.
1 mg ml-1 on HOPG
H21C10SC10H21:
(H21C10SH:
5.31 ± 0.76 nm
2.21 ± 0.12 nm)
1H
NMR Characterisation
g -protons
Periodate Oxidation
b -protons
a -protons
g
b
a
W ater
S
S
Upon heating the NMR sample
at 50ºC for 4 hours the gold
aggregated (gold film) and the
CDCl3 solution changed from
dark purple to light yellow.
H21C10SH
capped
gold
nanoparticles prepared in the
same way were stable under
the same conditions.
Oxidation in SAMs: M.T. Lee, C.C. Hsueh,
M.S. Freund, G.S. Ferguson
Langmuir, 1998, 14, 6419
S(O)
IR (1265 cm-1)
3.0
2.5
2.0
1.5
(ppm)
1.0
0.5
0.0
HREELS of Nanoparticulate Film
Nanoparticles assembled on graphite from solution (CDCl3) drop.
1 mg ml-1 on HOPG
Surface Analysis: Incident electron energy 4.5 eV (low energy)
C-Cstr
C-Hrock CH
2 sci
C-Hstr
Au-Svib
Electron irradiation will result in loss of Au-S band and hydrocarbon bands?….
HREELS of Nanoparticulate Film after Prolonged Electron
Exposure
…Nanoparticulate film irradiated with 50 eV electrons (high energy)
230 cm-1 mode disappeared: Au-S Bond broken (not elastic scattering broadening)
However, still have hydrocarbon…but less of it
Writing with an E-Beam
26 nm line width
Writing Nanogaps with an e-Beam
20 nm
150 nm
30 nm
S
SEM Image
Conclusions
Chemistry induced by an e-beam, has been - until recently - a little
studied area of research. The reason being it was thought that only
cross-linking or fragmentation were the only chemical processes.
However, with the maturity of the field of SAMs coupled with both the
advances in surface spectrocopic characterisation and technological
advances in e-beam writing, electrons are being studied as a reagent to
induce specific chemical transformations in SAMs.
Such an approach allows very sophisticated control over the tailoring of
surface properties on the nanoscale, and bodes well for the fabrication of
nanodevices.
April 19, 2004
NY Times Technology
The NY Times' brilliance rings through a recent article
about nanotechnology. The paper writes:
‘The term nanotechnology comes from the nanometer,
which is one-billionth of an inch.’