epitaxial graphene claire berger gatech- school of physics, atlanta cnrs-institut néel, grenoble...
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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