part 3ii electron beam lithography sams specific chemistry
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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.
Learning Objectives
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
e
beam
A single molecular monolayer
The e-beam initiates specific chemical reactions in the SAM.
Literally the electrons are a reagent!
…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
S
N O2
S
N O2
S
N O2
S
N O2
S
N O2
S
N O2
S
N O2
S
N H2
S
N H2
S
N O2
S
N O2
S
N O2
S
H N
S
H N
S
N O2
R1O
R1O
e-beam
A u
A u
A u
Ar-NO2 to Ar-NH2
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.
Excellent system as chemical reactivity between nitro and amino group is different.
AFM micrograph in frictional mode.
C/cm2
N=O symmetric stretching mode
Surface FT-IR
(a) 0(b) 10 000(c) 15 000(d) 27 000(e) 35 000
(f) Chemically Reduced
Characterising the Conversion
SAMs on Gold no good for electronic applications….
O2N O
Si(OMe)3
Film Formation
Immerse Si/SiO2 into 5 mM/anhy. THF under Ar
(Sonication at 25°C)Reaction times: 2 hours
Sonicate twice in fresh THF for 5 minRinse intensively with CHCl3, EtOH and UHP H2ODry under Ar
Film Characterisation:
Contact Angle (surface type)
AFM (roughness)
Elipsometry (thickness)
XPS (elemental composition)
NPPTMS
SAM on Si/SiO2
NO2
O
SiO
OO
Si
NO2
O
SiO
O
Si
NO2
O
SiO
O
Si
NO2
O
SiO
O
Si
NO2
O
SiO
O
Si
NO2
O
SiO
O
Si
1.1 nm
Langmuir 2004, 20, 3766-3768
(a) 3 min
(e) 447 min
(d) 273 min
(c) 163 min
(b) 97 min
NO 2 (405.6 eV)
NH 2 (399.6 eV)
Inte
nsi
ty /
arb
itra
ry u
nit
s
394399404409Binding energy / eV
XPS Chemical Modification
Secondary back scattered electrons initiate the chemistry
SAM Thickness (ellipsometry) = 1.2 0.2 nmCalculated = 1.1 nm
O
NH
Si
O
O
C
CF3
O
Si/SiO2
680685690695700Binding energy (eV)
Inte
nsi
ty (
arb
itra
ry u
nit
s)
F (1s)
• Immersion of the irradiated surface in a 10% TFAA solution in dry THF overnight
O
NH2
Si
O
O
Si/SiO2
Confirming the Chemical Transformation: NO2 to NH2
O
NO2
Si
O
O
Si/SiO2
• Immersion of the irradiated surface in a 10% TFAA solution in dry THF overnight
XPS
• E-beam
Patterning: Direct-Beam Writing
e
beam
5 m
NO2
NH2
SEM Image
primary beam energy
= 5 and 6 keV
doses between
= 25 and 300 µCcm-2
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.
S
NH2
S
NH2
S
NH2
S
NH2NH3
Citrate Stabiliser
Background: How to Increase Differentiation?
pH-Dependent Adsorption of Gold Nanoparticles on Aminothiophenol-Modified Gold Substrates
Tao Zhu, Xiaoyi Fu, Tao Mu, Jian Wang, Zhongfan Liu
Langmuir 1999, 15, 5197-5199
HO
CO2
CO2
CO2
--
-
--
- --
-
-
-
--
---
16 nmdiameter
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.
Generating Radicals
ATRP = Atom Transfer Radical Polymerisation
Monomers = styrene and methyl methacrylate Langmuir, 2003, 19, 4519
C-Br bond homolytically
cleaved induced by e-beam to
generate radicals
XPS Br (3d)
SAM before irradiation
SAM irradiation (2 mins)
SAM irradiation (4 mins)
SAM irradiation (6 mins)
Evidence for Loss of Br
Evidence for Polymerisation
5 m
30 nm step height
30 nm equates to ~ 50 monomer units
Etched with HF
AFM
AFM Line Section
Cleaving a R-S-S-R Bond
The RS-SR bond is weak 55kcal mol-1
The RS-SR can be electrochemically reductively cleaved.
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.
e
HHHH
- SPh
Langmuir, 2003, 19, 9748
N-(1-pyrene)maleimide
Trenches become Humps
AFM After IrradiationAFM After Irradiation
Chemically Backfilling the Trench
The nanopartices are rinsed away with an organic solvent, leaving the gold nanowire.
The electron beam initiates cleavage of Au-passivant interaction.
Writing Gold Nanowires: Negative Tone E-Beam Resist
Gold nanoparticles fuse together, and organic evaporates in UHV.
Film of Au nanoparticles
passivated with an
organic ligand
eeee
ee
eee
eeee
ee
J. Phys.: Condens. Matter, 2003, 15, S3047-S3063.
S S S S S
Organic passivant stops thenanoparticles aggregating
Gold-Thiolate Bond
The Organic Passivant
E-beam degrades the
passivant, leaving
carbonaceous residue in the
gold. Not exactly a good
conductor.
But
S S S S S S S S
SAM on planar gold formed from dialkylsulfides
Dialkyl SulfidesSAM on planar gold
formed from alkylthiols
Au-S Bond = 60 kJ mol-1
A New Passivant for Gold Nanoparticles
Alkyl Thiols
Au-S Bond = 120 kJ mol-1
D.J. Lavrich, S.M. Wetterer, S.L. Bernasek, G.J. Scoles, J. Phys. Chem. B 1998, 102, 3456
R.G. Nuzzo, F.A. Fusco, D.L. AllaraJ. Am. Chem. Soc., 1987, 109, 2358
E.B. Troughton, C.D. Bain, G.M. WhitesidesLangmuir, 1988, 4, 365
Synthesis of Nanoparticles
HAuCl4
(H2O)
N(Oct)4Br(PhMe)
N(Oct)4AuCl4
HBr
45 minutes
N(Oct)4AuCl4
Passivant
NaBH4 In water (30 mL)
Nanoparticle Solution
1. Separate PhMe layer
2. Precipitation (MeCN)
3. Centrifugation
SSH
C10SH C10SC10
Passivant
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
H21C10SC10H21: 5.31 ± 0.76 nm(H21C10SH: 2.21 ± 0.12 nm)
Nanoparticles assembled on graphite from solution (CDCl3) drop.1 mg ml-1 on HOPG
W ater
0.01.02.0 0.51.52.53.0
(ppm)
-protons
-protons
-protons
S
S
S(O)
1H NMR Characterisation
Periodate Oxidation
IR (1265 cm-1)
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. FergusonLangmuir, 1998, 14, 6419
HREELS of Nanoparticulate Film
Nanoparticles assembled on graphite from solution (CDCl3) drop.1 mg ml-1 on HOPG
C-Hstr
C-Hrock
C-Cstr
CH2 sci
Au-Svib
Electron irradiation will result in loss of Au-S band and hydrocarbon bands?….
Surface Analysis: Incident electron energy 4.5 eV (low energy)
HREELS of Nanoparticulate Film after Prolonged Electron Exposure
230 cm-1 mode disappeared: Au-S Bond broken (not elastic scattering broadening)
…Nanoparticulate film irradiated with 50 eV electrons (high energy)
However, still have hydrocarbon…but less of it
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.
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