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Part 3iii:
Scanning Near-FieldPhotolithography
(SNP)
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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
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Background
Some Surface Photo-oxidation Chemistry
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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
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HO
S
O
Ag
S
Ag
J. Am. Chem. Soc. 2001, 123, 4089-4090
Static SIMS
O3S
10 Mins Photooxidation
40 Mins Photooxidation
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Mask
Patterning the C60 Film
HS
HO
O
O3S
HO
O
HS
254 nmPhotooxidation
SIMS
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Background
An Atomic Force Microscope
(AFM)
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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
–V
C+
D
A B
C D
VA+C – VB+D
The Atomic Force Microscope Set-Up
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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.
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The AFM Cantilever and Tip
Tip
The Tip is an Atom!!
Atomic Resolution
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Background
Scanning Near Field Optical Microscope
(SNOM)
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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…
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SNOM/NSOMhttp://www.olympusmicro.com/primer/techniques/nearfield/nearfieldintro.html
Strands of DNAhttp://www.witec.de/pdf/alpha300Sflyer.pdf
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Example of SNP 1
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The SNOM as Lithography Tool
Scanning Near Field Photolithograpgy
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Au
SNOM
Scanning Near Field Photolithography, Oxidation and Back Filling
SH SO3 SH
CO2H
J. Am. Chem. Soc., 2002, 124, 2414
6 6 6
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J. Am. Chem. Soc., 2002, 124, 2414
CH3 CO2HLines
AFM (Friction Force Mode)
6 x 6 m
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Example of SNP 2
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Au
SNOM
11 11
Scanning Near Field Photolithography, Oxidation and Etching
Fe(CN)62+/Fe(CN)6
3+ (aq)30 mins
SH SO3
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Nanoletters, 2002, 11, 1223
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Example of SNP 4
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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
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O
Si
OHO
Si
OH
(ii) Incubate with Calf Thymus DNA
(i) Convert acid into active ester
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Example of SNP 4
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S SS
SS
S SS
SS
S O3 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
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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
S
SS
SS
SS
S S
SS
S S
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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
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Si/SiO2
10 nm
40 nm
2 nm
100 nm
Rinse
Si/SiO2
x
Si/SiO2
yz
Proposal: Scanning Near Field Photolithography (SNP)
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Si/SiO2
10 nm
40 nm
2 nm
100 nm
Rinse
Si/SiO2
x
Si/SiO2
yz
110 nm 14 nm
250 nm120 nm
Proposal: Scanning Near Field Photolithography (SNP)
This was a little disappointing as structures were
greater than 100 nm
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Water
Air
Solution? Making a Thinner Film of the Gold Nanoparticles
MoveableBarrier
Repeat to obtain a bilayer
Langmuir-Schaeffer Layer Structures
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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.
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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
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• 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
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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
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Substrate
Mask
Patterning the C60 Film
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0
50
100
150
200
250
300
0 0.5 1 1.5 2 2.5Writing speed (ms-1)
Lin
e w
idth
(n
m)
0.3 m s-1 1 m s-1 2 m s-1
Patterning the C60 Film with SNP
35 m s-1
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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.
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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.
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MAPPER
An array of around 14,000 direct write electron beams
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http://www.zurich.ibm.com/st/storage/concept.html#
Millipede
An Array of AFM cantilvers and tips