Transcript 14 presentation

Nanoimprinting of 2-D Graphene Nanowires
Jeremy R. Roth, Yen Peng Kong, Albert F. Yee
Challenges
Objective
Establish a process for patterning graphene using
Nano-Imprint Lithography for use in nano-scale
electronic circuitry.
Introduction
Researchers have found that
graphene, single layer
graphite, has unique electrical
and quantum properties.1-3
Graphene’s carbon nanotubelike scale and electrical
behavior make it attractive for
2-D electronic circuits.4
However a method to
commercially pattern graphene
must be developed if carbonbased electronics are to go
beyond mere laboratory
curiosities. This research is an
effort to evaluate the viability of
Nano-Imprint Lithography (NIL)
as a technique for patterning
graphene using certain
polymers as precursors (see
Patterning Process).
Challenges were to find a material and graphitization
process that are compatible with NIL and would
result in single layer graphene. This requires:
1. A precursor that may:
a. be patterned via an existing NIL technique, or
b. be incorporated into a new NIL technique
2. A NIL-compatible material process with reasonable
processing parameters (i.e. temperature, pressure)
3. A reliable approach to characterizing structures and
properties
Patterning Process
NIL Polymers
Literature Graphitizing
Polymers
Results
Conclusion
Conventional Graphitization
Non-catalytic graphitization
of PAN, PS and PVA was
attempted. Raman spectra
for PAN at heat treatment
temperatures from 500 to
800oC most closely match
Figure 6. Raman spectra of PAN heat treated at
that of glassy carbon15 rather 500 to 800 C for 10 minutes.
than graphite or graphene. A decrease in intensity with
respect to the Si peak can be seen likely due to thinning
from oxidation in the mostly inert atmosphere of the TGA.
Spectra for other materials was not possible due a failed
laser on the raman spectrometer used.
1. Graphitization of polymers alone requires
prohibitively high temperatures and high vacuum,
making it difficult to combine with a commercial
process such as NIL.
o
Catalyzed Graphitization
Graphitic C layer (formed upon heat treatment)
Conventional
Graphitization*
Material
Selection
Spin Coat onto Si Mold**
Catalytic
Graphitization
7 (a)
NIL Transfer to
Insulating Substrate
Catalytic Graphitization
Heat Treatment (500-900C)
Figure 1. Georgia Tech. lithographypatterned graphene and graphene
transistor from silicon carbide.5
Graphitization Heat Treatment
(1400-3000C + UHV)
Candidate Materials
NIL Transfer to
Insulating Substrate
Raman / SEM / AFM / STM Characterization
Common polymers like polyacrylonitrile (PAN),
polystyrene (PS) and polyvinyl alcohol (PVA) were first
considered for precursor materials to produce
graphene. Further materials were considered based on
their ability to graphitize after Franklin.6
Figure 3. Process for graphitizing NIL patterned polymer precursors for both catalyzed and conventional
graphitization approaches. * Not pursued due to lack of High Temperature / UHV facilities ** Spin coating was
done on flat wafers for simplicity. *** PVD films of Ni were created initiallyto study diffusion 12, 13. Steps in italics
indicate future work.
Nano-Imprint Lithography14
Step 3. Mold is released, nano-scale
features remain
PVC6
PVC7
PVC8
Anthracene9
Diamond8
Poly-11
paraphenylene
Pitch10
Napthalene7
Black
7
Pitch Coke
Step 1. Polymer is spin-coated onto
treated mold and positioned into NIL
press over patterning substrate
Figure 7. (a) Schematic of PAN/C:Ni systems
after Sinclair12. (b) Raman spectrum of Ni-C
PVD system.* SEM image of Ni-C PVD system
(c) heated to 700oC (d).
In figures 7(c)(d) and 7(b)(c) carbon appears to have
diffused through the nickel layer and nucleated on the
surface. Raman spectra for each are also similar to that
for glassy carbon15. This is not necessarily a negative
result for graphite as carbon below that did not diffuse
through the nickel could be the major source for these
spectra, masking any graphitic carbon formed on the
surface. *Thanks to Renishaw LLC for the raman data in
figures 7(b) and 8(a)
8 (b)
Step 2. Polymer-coated mold is pressed against
patterning substrate w/ specific temperature and pressure
Raman Spectroscopy
8(c)
Petroleum Coke7
Welsh Coking Coal6
8 (a)
1000oC
1500oC
2000oC
2500oC
3000oC
3500oC
Graphitization Temperature
Figure 2. Known graphitizing materials and their graphitization temperature
S ummer
U ndergraduate
2 R esearch
0 F ellowship in
0 I nformation
6 T echnology
ranges.6-11
Figure 4. Raman scattering of monochromatic laser light
from aromatic carbon sp2 hybrid bond15.
Figure 5. Raman spectra of
graphite and graphene16.
Future Work
• Study further carbon-catalyst systems and
configurations.
• Graphitize nano-imprint patterned polymeric carbon
precursors and analyze integrity of pattern after heat
treatment.
Acknowledgments
Polymer Carbonization Heat
Treatment (500-900C)
7 (b)
Pitch
Coke6
Petroleum Coke7
7 (d)
Si Wafer
3. SEM and raman spectroscopy have proven reliable
tools for characterizing these material processes.
• Use E-beam epitaxy to create single crystal systems
similar to the PVD systems shown in figure 6(a) in an
effort to create a continuous graphene sheet.
7 (c)
6nm Ni PVD Layer
4nm C PVD / carbonized PAN layer
Spin Coat onto (111)
Epitaxial Catalyst Mold***
2. Catalytic graphitization presents a promising avenue
for lowering processing temperature, making
graphene more compatible with NIL
Figure 8. (a) Raman spectrum of Ni-PAN PVD system.* (b) SEM
image of Ni heated to 800oC for 10 minutes. (c) Ni-PAN PVD
system, PAN carbonized at 700oC for 10 minutes, PVD Nickel
applied and heated to 800oC for 10 minutes .
[email protected] · www.research.calit2.net/students/surf-it2006 · www.calit2.net
My deepest gratitude to Said Shokair and UROP, Dr.
Tai Chen, Professor Eric Potma and Hyun Min Kim in
the department of Chemistry, the Mecartney / Mumm
group and the Calit2 staff for all their help and support.
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