2,238 research outputs found
Note about a second "evidence" for a WIMP annual modulation
This note, with its five questions, is intended to contribute to a
clarification about a claimed "evidence" by the DAMA group of an annual
modulation of the counting rate of a Dark Matter NaI(Tl) detector as due to a
neutralino (SUSY-LSP) Dark Matter candidate.Comment: LaTex, 3 pages, 2 figure
Impact of local stacking on the graphene-impurity interaction: theory and experiments
We investigate the graphene-impurity interaction problem by combining
experimental - scanning tunneling microscopy (STM) and spectroscopy (STS) - and
theoretical - Anderson impurity model and density functional theory (DFT)
calculations - techniques. We use graphene on the SiC(000-1)(2x2)_C
reconstruction as a model system. The SiC substrate reconstruction is based on
silicon adatoms. Graphene mainly interacts with the dangling bonds of these
adatoms which act as impurities. Graphene grown on SiC(000-1)(2x2)_C shows
domains with various orientations relative to the substrate so that very
different local graphene/Si adatom stacking configurations can be probed on a
given grain. The position and width of the adatom (impurity) state can be
analyzed by STM/STS and related to its local environment owing to the high bias
electronic transparency of graphene. The experimental results are compared to
Anderson's model predictions and complemented by DFT calculations for some
specific local environments. We conclude that the adatom resonance shows a
smaller width and a larger shift toward the Dirac point for an adatom at the
center of a graphene hexagon than for an adatom just on top of a C graphene
atom.Comment: 13 pages, 6 figures, Accepted for publication in Phys. Rev.
Quasiparticle Chirality in Epitaxial Graphene Probed at the Nanometer Scale
Graphene exhibits unconventional two-dimensional electronic properties
resulting from the symmetry of its quasiparticles, which leads to the concepts
of pseudospin and electronic chirality. Here we report that scanning tunneling
microscopy can be used to probe these unique symmetry properties at the
nanometer scale. They are reflected in the quantum interference pattern
resulting from elastic scattering off impurities, and they can be directly read
from its fast Fourier transform. Our data, complemented by theoretical
calculations, demonstrate that the pseudospin and the electronic chirality in
epitaxial graphene on SiC(0001) correspond to the ones predicted for ideal
graphene.Comment: 4 pages, 3 figures, minor change
A Calibrated Time Domain Envelope Measurement System for the Behavioral Modeling of Power Amplifiers
This paper presents a set-up which enables the generation and the calibrated time domain measurements of complex envelopes of modulated signals at both ports of non linear microwave power amplifiers. The architecture of the characterization tool is given. Examples of error corrected time domain envelopes at the input / output RF ports of a 36 dBm output power – 30dB power gain L-band SSPA are shown. Futhermore, the use of this characterization tool and a suitable processing of measurement data are applied to a novel measurement based behavioral modeling approach of non linear devices accounting for memory effects
Graphene on the C-terminated SiC (000 ) surface: An ab initio study
The atomic and electronic structures of a graphene layer on top of the
reconstruction of the SiC (000) surface are studied from
ab initio calculations. At variance with the (0001) face, no C bufferlayer is
found here. Si adatoms passivate the substrate surface so that the very first C
layer presents a linear dispersion characteristic of graphene. A small
graphene-substrate interaction remains in agreement with scanning tunneling
experiments (F.Hiebel et al. {\it Phys. Rev. B} {\bf 78} 153412 (2008)). The
stacking geometry has little influence on the interaction which explains the
rotational disorder observed on this face.Comment: 4 pages, 3 figures, additional materia
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