Raman Spectroscopy of Graphene Edges - Graphene and Its Fascinating Attributes - page 91

Chapter 6

Raman Spectroscopy of Graphene Edges

Riichiro Saito
Department of Physics, Tohoku University, Sendai 980-8578, Japan
[e-mail]

Raman spectroscopy of graphene edges is overviewed mainly from the
theoretical point of view. There are two symmetric edge structures of
graphene, armchair and zigzag edges. Because of the symmetry, a differ-
ent Raman spectra and its polarization dependence are predicted within
the bond-polarization theory. This result is useful for characterization
of the edge structure.

1. Introduction

Graphene is a one atomic layer of graphite. Since graphite is known to be
micro-clevaged into thin layers of graphene up to one atomic layer and up
to 100 m in size on the substrate by a rather simple method using Scotch

tape, many researchers have measured one atomic layer of graphene 1-8
without using a special nano-technology. Graphene is a two-dimensional
solid and the electronic structure of graphene has a unique character at
the Fermi energy, such as massless Fermion particle and zero energy gap at
the hexagonal corner of two dimensional (2D) Brillouin zone. In the case
of graphite, on the other hand, because of inter-layer interaction between
two graphene layers smears out the uniqueness of the electronic structure
and semi-metallic nature might be seen, though some exotic character of
graphene (high mobility) can still be seen.
An important message of graphene physics especially in the transport
properties is that the mobility of a suspended graphene is very high (up to
200,000cm 2 /Vs) even at room temperature. Thus once we get an energy
gap for graphene, we can make a field effect transistor with high on-off
switching ratio which can operate at a high frequency up to 100GHz which
is a big challenge for new semiconducting devices. In a graphene device,

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