Part 3iii: Scanning Near-Field Photolithography (SNP)

Part 3iii:

Scanning Near-FieldPhotolithography

(SNP)

After completing PART 3iii of this course you should have an understanding of, and be

able to demonstrate, the following terms, ideas and methods.

(i) The photo-oxidation process of thiolates to sulfonates on gold,

(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,

(iv) Appreciate the various chemistries that are initiated by the radiation,

(v) Appreciate how an AFM operates,

(vi) Appreciate how a SNOM operates, and

(vii) Appreciate how SNP works

Learning Objectives

Background

Some Surface Photo-oxidation Chemistry

Photoxidation of Thiol SAMs on Golds and Silver

J. Am. Chem. Soc. 1993, 115, 5305

SO3

I Hr UV irradiation in air

Immersion for 1 Hr in 1 mMHexane thiol solution

SH

XPS

HO

S

O

Ag

S

Ag

J. Am. Chem. Soc. 2001, 123, 4089-4090

Static SIMS

O3S

10 Mins Photooxidation

40 Mins Photooxidation

Mask

Patterning the C60 Film

HS

HO

O

O3S

HO

O

HS

254 nmPhotooxidation

SIMS

Background

An Atomic Force Microscope

(AFM)

CPU

PowerSupply

Piezo

Cantilever / Tip Assembly

Path tip follows

Motion

X

Y

ZMotion

X

Y

Z

Substrate

Image Display

Four Quadrant Photodetector (set-point)

Laser BeamVA

+B–

VC

+D A B

C D

VA+C – VB+D

The Atomic Force Microscope Set-Up

Piezoelectric scanners for AFMs usually can translate in three directions (x, y, and z axes) and come in different sizes to allow maximum scan ranges of 0.5 to 125 microns in the x and y axes and several microns in the vertical (z) axis. A well-built scanner can generate stable motion on a scale below 1 Angstrom.

By scanning the AFM cantilever over a sample surface (or scanning a sample under the cantilever) and recording the deflection of the cantilever, the local height of the sample is measured. Three-dimensional topographical maps of the surface are then constructed by plotting the local sample height versus horizontal probe tip position

A key element of the AFM is its force sensor, or cantilever. The cantilever is usually formed by one or more beams of silicon or silicon nitride that is 100 to 500 microns long and about 0.5 to 5 microns thick. Mounted on the end of the cantilever is a sharp tip that is used to sense a force between the sample and tip. For normal topographic imaging, the probe tip is brought into continuous or intermittent contact with the sample and scanned over the surface. Fine-motion piezoelectric scanners generate the precision motion needed to generate topographic images and force measurements. A piezoelectric scanner is a device that moves by a sub-nanomtere amounts when a voltage is applied across its electrodes. Depending on the AFM design, scanners are used to translate either the sample under the cantilever or the cantilever over the sample.

The AFM Cantilever and Tip

Tip

The Tip is an Atom!!

Atomic Resolution

Background

Scanning Near Field Optical Microscope

(SNOM)

SNOM/NSOMhttp://www.olympusmicro.com/primer/techniques/nearfield/nearfieldhome.html

Drawn or etched fibre optic cable appended to AFM cantilever

Or hole made in the end of an AFM tip

Aperture ~50 nm

Wavelength of light 180-300 nm

i.e. longer than the aperture

~10 nm

Which is limited by being used in the near field

Therefore diffraction…

SNOM/NSOMhttp://www.olympusmicro.com/primer/techniques/nearfield/nearfieldintro.html

Strands of DNAhttp://www.witec.de/pdf/alpha300Sflyer.pdf

Example of SNP 1

The SNOM as Lithography Tool

Scanning Near Field Photolithograpgy

Au

SNOM

Scanning Near Field Photolithography, Oxidation and Back Filling

SH SO3 SH

CO2H

J. Am. Chem. Soc., 2002, 124, 2414

6 6 6

J. Am. Chem. Soc., 2002, 124, 2414

CH3 CO2HLines

AFM (Friction Force Mode)

6 x 6 m

Example of SNP 2

Au

SNOM

11 11

Scanning Near Field Photolithography, Oxidation and Etching

Fe(CN)62+/Fe(CN)6

3+ (aq)30 mins

SH SO3

Nanoletters, 2002, 11, 1223

Example of SNP 4

O

Si

OH

NANO LETTERS, 2006, 6, 29-33

Chemical Modifying the SAM Surface Group

Cl

Si Si

O

Si

O

Si

OH

h h[O] DNA

O

Si

OHO

Si

OH

(ii) Incubate with Calf Thymus DNA

(i) Convert acid into active ester

Example of SNP 4

S SS

SS

S SS

SS

SO3 SO3 SO3SO3SO3

S O3S O3 S O3S O3

OS 3

UV Radiation

Aggregation of Gold

Writing to Gold Nanoparticles on SiO2

Nanoletters, 2006, 6, 345

Spinning

Si/SiO2

Volatile solvent

Solventevaporates

Making a Thin Film of Nanoparticles: Spin Coating

Decane thiol passivated gold nanoparticles (1-3 nm)

M. Brust, M. Walker, D. Bethell, D. J. Schiffrin, R. Whyman, J. Chem. Soc., Chem. Commun., 1994, 801-802.

S

S

S

SSS

S SSS

S S

SS

S S

Si/SiO2

UV Masks

Parallel Exposure to 244 nm photons

Rinse

Si/SiO2

Si/SiO2

10m

40nm

2nm

Making 3D Micron Scale Structures Irradiation/Rinsing

Unirradiated particles rinse away

70 nm

Si/SiO2

10 nm

40 nm

2 nm100 nm

Rinse

Si/SiO2

x

Si/SiO2

yz

Proposal: Scanning Near Field Photolithography (SNP)

Si/SiO2

10 nm

40 nm

2 nm100 nm

Rinse

Si/SiO2

x

Si/SiO2

yz

110 nm 14 nm

250 nm 120 nm

Proposal: Scanning Near Field Photolithography (SNP)

This was a little disappointing as structures were

greater than 100 nm

Water

Air

Solution? Making a Thinner Film of the Gold Nanoparticles

MoveableBarrier

Repeat to obtain a bilayer

Langmuir-Schaeffer Layer Structures

Langmuir-Schaeffer Bilayers and SNP Structures

60 nm

~ SNOM Aperture

6 nm High

~2 x diameter of the particles

60 nm structures indicates that the excitation does not spread outside the area illuminated by the probe, in contrast to the behavior observed for the spin-cast films.

The structures are continuous and appear generally free from defects, with some thinning.

Making Carbon Nanowires with

Photons:Scanning Near Field

Photolithography

1m+-

ee

Writing Wires

Parvez IqbalParvez Iqbal††, Marcus D Hanswell, Marcus D Hanswell‡‡, Shuqing Sun,, Shuqing Sun,## Tim Richardson Tim Richardson‡‡, G. Leggett, G. Leggett## and Jon A. Preeceand Jon A. Preece††

††School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TTSchool of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT

‡‡ Department of Physics and Astronomy, University of Sheffield, S3 7RHDepartment of Physics and Astronomy, University of Sheffield, S3 7RH

School of Chemistry, University of Sheffield,Western Bank, Sheffield, S10 2TN School of Chemistry, University of Sheffield,Western Bank, Sheffield, S10 2TN

• Rao et al. demonstrated UV light exposure on C60 film led to a insoluble material in toluene

• Through Raman and infrared spectroscopy, x-ray diffraction and Laser desorption mass spectroscopy concluded that the exposed C60 film underwent photopolymerisation (2 + 2 cycloaddition)

UV light

M. Rao, P. Zhou, K.-A. Wang, G. T. Hagar, J. M. Holden, Y. Wang, W.-T. Lee, X.-X. Bi, P. C. Eklund, D. S. Cornett, . M. A. Duncan, I. J. Amster, Science, 1993, 259, 955

Reaction of C60 Under UV Light Exposure

For Yr2 and Yr3 Chemists!!

2s + 2s Photochemical Cycloaddition

LUMO (ene)SOMO (ene)Combination

~ 1 nm

Water

AirO O

O O

O

O

O

O

O

O

OH HO

Making a Thin Film of C60

~ 2.5 nm

MoveableBarrier

Langmuir-Blodgett Layer Structures

5 mm min-1

Substrate

Mask

Patterning the C60 Film

0

50

100

150

200

250

300

0 0.5 1 1.5 2 2.5Writing speed (ms-1)

Lin

e w

idth

(nm

)

0.3 m s-1 1 m s-1 2 m s-1

Patterning the C60 Film with SNP

35 m s-1

Conclusions on SNP

SNP is a very facile and versatile route to create nanostructured surfaces, with resolution better than photolithography and almost equalling EBL.

It requires relatively cheap instrumentation and is carried out under ambient conditions.

Only the tip of the iceberg has been looked at to date as to what type of SAMs and functional groups might be modified, and there is a whole host of chemical reactions that have been studied in the solution phase that could be transferred to the surface.

Major disadvantage of SNP (and EBL) is that it is a serial process and therefore slow, unlike photolithography.

Summing Up Part 3

Photolithography is a rapid parallel process, but is struggling with to keep pace with Moore’s law.

E-beam lithography is a slow serial process, but can create nanoscale structures. However, it requires the use of expensive intrumentation and UHV conditions.

SNP is a slow serial process, but can also create nanoscale structures. In addition, it is a relative cheap and facile methodology, being carried out under ambient conditions.

MAPPERAn array of around 14,000 direct write electron beams

http://www.zurich.ibm.com/st/storage/concept.html#

Millipede

An Array of AFM cantilvers and tips