Elena Stolyarova, Kwang Taeg Rim, Sunmin Ryu, Janina Maultzsch, Philip Kim, Louis E' Brus, Tony F' H

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High-resolution scanning tunneling microscopy
imaging of mesoscopic graphene sheets on an
insulating surface
Elena Stolyarova, Kwang Taeg Rim, Sunmin Ryu,
Janina Maultzsch, Philip Kim, Louis E. Brus, Tony
F. Heinz, Mark S. Hybertsen, and George W. Flynn
Presented by Maria Moura
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The strength of interaction between the
underlying substrate and the graphene film is an
issue of importance in the study of these
materials of monolayer thickness
Experiment
- Sample prepared on a SiO2 surface by direct
exfoliation of crystalline graphite
- Single-layer films were identified by using
Raman spectroscopy
- Samples were produced under ambient conditions
and then subjected to microfabrication processing
and exposure to various organic solvents
- STM images of single-layer graphene crystals
were examined under ultrahigh vacuum conditions
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Optical microscopy images
I single-layer
II multi-layer (5)
III SiO2 coated substrate (insulating)
After electrode deposition around the flake
1V sample potential
18 nm layer of Au
darker region is the uncovered part
Most of the single-layer region and a portion of
the multilayer region are accessible for STM
studies
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Single-layer honeycomb Expected for the full
hexagonal symmetry of an isolated graphene
monolayer
STM images
No atomic defects
Few layers reduced threefold symmetry
Characteristic of the surface of bulk graphite
(2 or more layers)
5
Stereoscopic, large-area (100 x 62 nm) STM image
of single-layer
Z scale is enlarged
Height variation of 0.5 nm, lateral scale of 10 nm
Height comparable to underlying SiO2 surface (AFM)
ripples of 0.5 nm high and 5 nm wide
Free standing sheet
Meyer et al. Nature 446 (07)
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Conclusions
STM images of graphene sheets on insulating
substrate display a symmetric honeycomb
structure, with no atomic defects, and exhibits
rippling
Points of discussion

• Fluctuation in height is relatively modest
• height variation of 0.5 nm, bond length 0.142 nm

• Roughness may arise from the graphene film
  following
• (at least partially) the features of the
  underlying SiO2 surface

• STM application of elastic forces on sample.
• Single-layer graphene sheets are especially
  susceptible to deformation resulting from such
  forces, which also may contribute to the observed
  large-scale topography