200 research outputs found
Interplay between interferences and electron-electron interactions in epitaxial graphene
We separate localization and interaction effects in epitaxial graphene
devices grown on the C-face of a 4H-SiC substrate by analyzing the low
temperature conductivities. Weak localization and antilocalization are
extracted at low magnetic fields, after elimination of a geometric
magnetoresistance and subtraction of the magnetic field dependent Drude
conductivity. The electron electron interaction correction is extracted at
higher magnetic fields, where localization effects disappear. Both phenomena
are weak but sizable and of the same order of magnitude. If compared to
graphene on silicon dioxide, electron electron interaction on epitaxial
graphene are not significantly reduced by the larger dielectric constant of the
SiC substrate
Selective epitaxial growth of graphene on SiC
We present an innovative method of selective epitaxial growth of few layers
graphene (FLG) on a pre-patterned SiC substrate. The methods involves,
successively, the sputtering of a thin AlN layer on top of a mono-crystalline
SiC substrate and, then, patterning it with e-beam lithography (EBL) and wet
etching. The sublimation of few atomic layers of Si from the SiC substrate
occurs only through the selectively etched AlN layer. The presence of the Raman
G-band at ~1582 cm-1 in the AlN-free areas is used to validate the concept, it
gives absolute evidence of the selective FLG growth.Comment: comments: 3 pages, reference 3 replace
Growth of monolayer graphene on 8deg off-axis 4H-SiC (000-1) substrates with application to quantum transport devices
Using high temperature annealing conditions with a graphite cap covering the
C-face of an 8deg off-axis 4H-SiC sample, large and homogeneous single
epitaxial graphene layers have been grown. Raman spectroscopy shows evidence of
the almost free-standing character of these monolayer graphene sheets, which
was confirmed by magneto-transport measurements. We find a moderate p-type
doping, high carrier mobility and half integer Quantum Hall effect typical of
high quality graphene samples. This opens the way to a fully compatible
integration of graphene with SiC devices on the wafers that constitute the
standard in today's SiC industry.Comment: 11 pages, 4 figures , Submitted in AP
Early stage formation of graphene on the C-face of 6H-SiC
An investigation of the early stage formation of graphene on the C-face of
6H-SiC is presented. We show that the sublimation of few atomic layers of Si
out of the SiC substrate is not homogeneous. In good agreement with the results
of theoretical calculations it starts from defective sites, mainly dislocations
that define nearly circular flakes, which have a pyramidal, volcano-like, shape
with a center chimney where the original defect was located. At higher
temperatures, complete conversion occurs but, again, it is not homogeneous.
Within the sample surface the intensity of the Raman G and 2D bands, evidences
non-homogeneous thickness.Comment: 12 pages, 3 figure
Investigation of Long Monolayer Graphene Ribbons grown on Graphite Capped 6H-SiC (000-1)
We present an investigation of large, isolated, graphene ribbons grown on the
C-face of on-axis semi-insulating 6H-SiC wafers. Using a graphite cap to cover
the SiC sample, we modify the desorption of the Si species during the Si
sublimation process. This results in a better control of the growth kinetics,
yielding very long (about 300 microns long, 5 microns wide), homogeneous
monolayer graphene ribbons. These ribbons fully occupy unusually large terraces
on the step bunched SiC surface, as shown by AFM, optical microscopy and SEM.
Raman spectrometry indicates that the thermal stress has been partially relaxed
by wrinkles formation, visible in AFM images. In addition, we show that despite
the low optical absorption of graphene, optical differential transmission can
be successfully used to prove the monolayer character of the ribbons
Angle-resolved photoemission study and first principles calculation of the electronic structure of GaTe
The electronic band structure of GaTe has been calculated by numerical atomic
orbitals density-functional theory, in the local density approximation. In
addition, the valence-band dispersion along various directions of the GaTe
Brillouin zone has been determined experimentally by angle-resolved
photoelectron spectroscopy. Along these directions, the calculated valence-band
structure is in good concordance with the valence-band dispersion obtained by
these measurements. It has been established that GaTe is a direct-gap
semiconductor with the band gap located at the Z point, that is, at Brillouin
zone border in the direction perpendicular to the layers. The valence-band
maximum shows a marked \textit{p}-like behavior, with a pronounced anion
contribution. The conduction band minimum arises from states with a comparable
\textit{s}- \textit{p}-cation and \textit{p}-anion orbital contribution.
Spin-orbit interaction appears to specially alter dispersion and binding energy
of states of the topmost valence bands lying at . By spin-orbit, it is
favored hybridization of the topmost \textit{p}-valence band with deeper
and flatter \textit{p}-\textit{p} bands and the valence-band minimum at
is raised towards the Fermi level since it appears to be determined by
the shifted up \textit{p}-\textit{p} bands.Comment: 7 text pages, 6 eps figures, submitted to PR
LA CIUDAD DESDE EL MUELLE [Material gráfico]
FOTO POSTAL DE "LAS PALMAS VISTA DESDE EL MUELLE". DUPLICADO DE LA IMAGEN Nº 2871Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201
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