133 research outputs found
How the SiC substrate impacts graphene atomic and electronic structures
Graphene, the two-dimensional form of carbon presents outstanding electronic
and transport properties. This gives hope for the development of applications
in nanoelectronics. However, for industrial purpose, graphene has to be
supported by a substrate. We focus here on the graphene-on-SiC system to
discuss how the SiC substrate interacts with the graphene layer and to show the
effect of the interface on graphene atomic and electronic structures.Comment: 3 pages, 3 figure
Magnetospectroscopy of epitaxial few-layer graphene
The inter-Landau level transitions observed in far-infrared transmission
experiments on few-layer graphene samples show a behaviour characteristic of
the linear dispersion expected in graphene. This behaviour persists in
relatively thick samples, and is qualitatively different from that of thin
samples of bulk graphite.Comment: Invited short review to appear in a special issue of Solid State
Communication
The structural properties of the multi-layer graphene/4H-SiC(000-1) system as determined by Surface X-ray Diffraction
We present a structural analysis of the multi-layer graphene-4HSiC(000-1})
system using Surface X-Ray Reflectivity. We show for the first time that
graphene films grown on the C-terminated (000-1}) surface have a
graphene-substrate bond length that is very short (0.162nm). The measured
distance rules out a weak Van der Waals interaction to the substrate and
instead indicates a strong bond between the first graphene layer and the bulk
as predicted by ab-initio calculations. The measurements also indicate that
multi-layer graphene grows in a near turbostratic mode on this surface. This
result may explain the lack of a broken graphene symmetry inferred from
conduction measurements on this system [C. Berger et al., Science 312, 1191
(2006)].Comment: 9 pages with 6 figure
Synthesis and characterization of atomically-thin graphite films on a silicon carbide substrate
This paper reports the synthesis and detailed characterization of graphite
thin films produced by thermal decomposition of the (0001) face of a 6H-SiC
wafer, demonstrating the successful growth of single crystalline films down to
approximately one graphene layer. The growth and characterization were carried
out in ultrahigh vacuum (UHV) conditions. The growth process and sample quality
were monitored by low-energy electron diffraction, and the thickness of the
sample was determined by core level x-ray photoelectron spectroscopy.
High-resolution angle-resolved photoemission spectroscopy shows constant energy
map patterns, which are very sharp and fully momentum-resolved, but nonetheless
not resolution limited. We discuss the implications of this observation in
connection with scanning electron microscopy data, as well as with previous
studies
Raman Topography and Strain Uniformity of Large-Area Epitaxial Graphene
We report results from two-dimensional Raman spectroscopy studies of
large-area epitaxial graphene grown on SiC. Our work reveals unexpectedly large
variation in Raman peak position across the sample resulting from inhomogeneity
in the strain of the graphene film, which we show to be correlated with
physical topography by coupling Raman spectroscopy with atomic force
microscopy. We report that essentially strain free graphene is possible even
for epitaxial graphene.Comment: 10 pages, 3 figure
New Synthesis Method for the Growth of Epitaxial Graphene
As a viable candidate for an all-carbon post-CMOS electronics revolution,
epitaxial graphene has attracted significant attention. To realize its
application potential, reliable methods for fabricating large-area
single-crystalline graphene domains are required. A new way to synthesize high
quality epitaxial graphene, namely "face-to-face" method, has been reported in
this paper. The structure and morphologies of the samples are characterized by
low-energy electron diffraction, atomic force microscopy, angle-resolved
photoemission spectroscopy and Raman spectroscopy. The grown samples show
better quality and larger length scales than samples grown through conventional
thermal desorption. Moreover the graphene thickness can be easily controlled by
changing annealing temperature.Comment: 16 pages and 7 figure
Raman spectra of epitaxial graphene on SiC and of epitaxial graphene transferred to SiO2
Raman spectra were measured for mono-, bi- and trilayer graphene grown on SiC
by solid state graphitization, whereby the number of layers was pre-assigned by
angle-resolved ultraviolet photoemission spectroscopy. It was found that the
only unambiguous fingerprint in Raman spectroscopy to identify the number of
layers for graphene on SiC(0001) is the linewidth of the 2D (or D*) peak. The
Raman spectra of epitaxial graphene show significant differences as compared to
micromechanically cleaved graphene obtained from highly oriented pyrolytic
graphite crystals. The G peak is found to be blue-shifted. The 2D peak does not
exhibit any obvious shoulder structures but it is much broader and almost
resembles a single-peak even for multilayers. Flakes of epitaxial graphene were
transferred from SiC onto SiO2 for further Raman studies. A comparison of the
Raman data obtained for graphene on SiC with data for epitaxial graphene
transferred to SiO2 reveals that the G peak blue-shift is clearly due to the
SiC substrate. The broadened 2D peak however stems from the graphene structure
itself and not from the substrate.Comment: 27 pages, 8 figure
Rayleigh Imaging of Graphene and Graphene Layers
We investigate graphene and graphene layers on different substrates by
monochromatic and white-light confocal Rayleigh scattering microscopy. The
image contrast depends sensitively on the dielectric properties of the sample
as well as the substrate geometry and can be described quantitatively using the
complex refractive index of bulk graphite. For few layers (<6) the
monochromatic contrast increases linearly with thickness: the samples behave as
a superposition of single sheets which act as independent two dimensional
electron gases. Thus, Rayleigh imaging is a general, simple and quick tool to
identify graphene layers, that is readily combined with Raman scattering, which
provides structural identification.Comment: 8 pages, 9 figure
Probing Mechanical Properties of Graphene with Raman Spectroscopy
The use of Raman scattering techniques to study the mechanical properties of
graphene films is reviewed here. The determination of Gruneisen parameters of
suspended graphene sheets under uni- and bi-axial strain is discussed and the
values are compared to theoretical predictions. The effects of the
graphene-substrate interaction on strain and to the temperature evolution of
the graphene Raman spectra are discussed. Finally, the relation between
mechanical and thermal properties is presented along with the characterization
of thermal properties of graphene with Raman spectroscopy.Comment: To appear in the Journal of Materials Scienc
Technique for the Dry Transfer of Epitaxial Graphene onto Arbitrary Substrates
In order to make graphene technologically viable, the transfer of graphene
films to substrates appropriate for specific applications is required. We
demonstrate the dry transfer of epitaxial graphene (EG) from the C-face of
4H-SiC onto SiO2, GaN and Al2O3 substrates using a thermal release tape. We
further report on the impact of this process on the electrical properties of
the EG films. This process enables EG films to be used in flexible electronic
devices or as optically transparent contacts.Comment: 8 pages, 4 figures and supplementary info regarding procedure for
transfe
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