SiC steps

1
4H-SiC substrate preparation - graphitization
Polished SiC substrate
SiC steps
Graphitized substrate
2
Patterning
3
e-beam lithography
Hall bar
FET
Quantum Interference loop
4
Epitaxial graphene grown on SiC
Highly ordered and well defined
material Transport layer is protected Graphene
properties Dirac - chiral electrons Anomalous
Berrys phase Weak anti-localization Landau
level spectrum Long electronic phase coherence
length Ballistic properties, high
mobility Anomalous transport no quantum Hall
effect periodic and fractal-like spectrum for
high mobility samples
AFM
5
Magneto-transport of a wide Hall bar (EG on
Si-face)
Shubnikov - de Haas magnetoresistance maxima
6
Magneto-transport and Landau levels
Dirac particles linear E(k)
n
3
2
EF
1
0
0
-1
-2
-3
Normal electrons quadratic E(k)
EF
Landau plot Slope gives carrier density
ns 1.3 1012cm-2 Intercept at n0 indicates
anomalous Berrys phase
see K. Novoselov et al. Nature 438, 197
(2005) Y. Zhang et al. Nature 438, 201 (2005)
W.de Heer et al., cond-mat /0704.0285
7
Temperature dependence of the SdH peaks
Landau levels thermally populated
Lifshitz-Kosevich equation A(T)/Ao
u/sinh(u) where u2p2kBT/?E(B)
Energy
Magnetic field
DE/kB(K)
1
?E(B)
vF0.75 106m/s
0
T
e
m
p
e
r
a
t
u
r
e

V. Gusynin, Phys. Rev. B 71,125124 (2005)
8
Transport is graphene-like surprising 3
layers Low mobility µ1100 cm2/Vs Disordered as
seen in STM (graphene on Si-face) Phase
coherence length lf(T4K)100nm
In agreement with STM-STS Scattering by defects
for graphene on the Si-face
G. Rutter, J. Stroscio et al., Science to be
published P. Mallet, J.-Y.Veuillen et al.
cond-mat/0702406
9
Interface charging
Interface layer dominates transport Neutral
layers seen in Landau level IR spectroscopy
Sadowski PRL97, 266405 (2006)
Graphene layers
SiC
Workfunction graphite-Workfunction SiC ?V 0.3
eV Built-in electric field
E ?V/L L is of order of screening
length. Hence interface layer is charged
ns E/?0 1012/cm2 (Note n1010/cm2 for
neutral graphite)
See also photoemission ARPES - A. Botswick et
al. Nature Physics 3, 36 (2007) E. Rolling et al.
cond-mat/0512226 (2005) - J. Phys Chem Solid 67,
2172 (2006) T. Seyller et al. , Surface Science
600, 3906 (2006).