part 3ii electron beam lithography sams specific chemistry

Part 3ii

Electron Beam Lithography

SAMs

Specific Chemistry

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.





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.





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

Converting an Aromatic Nitro Group

to an Aromatic Amine

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.

Self-Assembling into the Third Dimension

NO2

NH2

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

570nm

2.6µm

180nm

Adsorption of Particles to e-Beam Patterned Surface at pH 4.5

3.9µm

AFM Images

510nm2.9µm

90 nm

And Our Smallest Result to Date!

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.





"So how does physics save lives?" he persisted.

"It usually keeps the idiots like you out of medical school," replied the professor.

Initiating Radical ChemistryAnd Surface Polymer

Chemistry

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)



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

Cutting a Disulfide Bond

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

Loss of the S-Ph moiety to the vacuum

Writing with the e-Beam: Making Nanotrenches

N-(1-pyrene)maleimide

Trenches become Humps

AFM After IrradiationAFM After Irradiation

Chemically Backfilling the Trench

‘Welding’ Gold Nanoparticles Together!

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

Writing with an E-Beam

26 nm line width

Writing Nanogaps with an e-Beam

SEM Image

150 nm

20 nm

30 nm

S

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.’

part 3ii electron beam lithography sams specific chemistry

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