Epitaxial graphene

Claire BergerGATECH- School of Physics, Atlanta

CNRS-Institut Néel, Grenoble

NIRTNanopatterne

dEpitaxial graphite

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Motivation : Carbon nanotube transistors

Motivation : Multiwalled carbon nanotubes are ballistic conductors at room temperature

T. Ando, T. Nakanishi and R. SaitoJ. Phys. Soc. Jpn. 67, 2857 (1998)

“The absence of backward scattering is shown to be ascribed to Berry's phase which corresponds to a sign change of the wave function under a rotation of a neutrino-like particle* in the wave vector space in a two-dimensional graphite”

*i.e obeying the Dirac-Weyl equation

Quantized ballistic conductance

Nanotube fiber

- L (µm)

G (

2e2 /

h)

L

V

EF

1D metallic sub-bands Semiconducting Ntube

Nanotube Electronic Structure

Band structure of graphene

Linear dispersion Symmetry electrons - holes

PseudospinChirality

)ˆ,ˆ,ˆ(ˆ zyx σσσσ =

€

σ x =0 1

1 0

⎛

⎝ ⎜

⎞

⎠ ⎟;σ y =

0 −i

i 0

⎛

⎝ ⎜

⎞

⎠ ⎟

€

H = vF ⋅ ˆ σ ⋅ p

€

E = ±vF p

T. Ando, J. Phys. Soc. Jpn 67 (1998) 2857

Graphene ribbons

Metallic ribbonsSemiconducting or metallic ribbons

Graphene ribbons should retainthe essential properties of carbon nanotubes

M. Y. Han, B. Özyilmaz, Y. Zhang, P. Kim, Cond. Mat. 0702511

E =0.2 eV.nm W*=16 nm

Energy gap in exfoliated graphene ribbons

from Philip Kim, Columbia University

Gap Eg= E W-W*)

Thermal decomposition of SiC at high temperature (~1400oC) - high vacuum

after surface flattening by hydrogen etching

Epitaxial growth of graphene layers on 4H-SiC

graphiteSiC

LEED3 graphene layers

A.Charrier et al., J. Applied Physics 92, 2479 (2002)

C. Berger et al., Journal of Physical Chemistry B 108, 19912 (2004)

Si

C

Si Si

Graphene

on SiC

SiC

(0001) Si-face

(0001) C-face

By controling temperature, growth of 1 to ~100 graphene layers