415 research outputs found
Intrinsic Electrical Transport Properties of Monolayer Silicene and MoS2 from First Principles
The electron-phonon interaction and related transport properties are
investigated in monolayer silicene and MoS2 by using a density functional
theory calculation combined with a full-band Monte Carlo analysis. In the case
of silicene, the results illustrate that the out-of-plane acoustic phonon mode
may play the dominant role unlike its close relative - graphene. The small
energy of this phonon mode, originating from the weak sp2 bonding between Si
atoms, contributes to the high scattering rate and significant degradation in
electron transport. In MoS2, the longitudinal acoustic phonons show the
strongest interaction with electrons. The key factor in this material appears
to be the Q valleys located between the {\Gamma} and K points in the first
Brillouin zone as they introduce additional intervalley scattering. The
analysis also reveals the potential impact of extrinsic screening by other
carriers and/or adjacent materials. Subsequent decrease in the actual
scattering rate can be drastic, warranting careful consideration. Finally, the
effective deformation potential constants are extracted for all relevant
intrinsic electron-phonon scattering processes in both materials
First Principles Analysis of Electron-Phonon Interaction in Graphene
The electron-phonon interaction in monolayer graphene is investigated by
using density functional perturbation theory. The results indicate that the
electron-phonon interaction strength is of comparable magnitude for all four
in-plane phonon branches and must be considered simultaneously. Moreover, the
calculated scattering rates suggest an acoustic phonon contribution that is
much weaker than previously thought, revealing the role of optical phonons even
at low energies. Accordingly it is predicted, in good agreement with a recent
measurement, that the intrinsic mobility of graphene may be more than an order
of magnitude larger than the high values reported in suspended samples.Comment: 12 pages, 4 figure
Torsional response and stiffening of individual multi-walled carbon nanotubes
We report on the characterization of torsional oscillators which use
multi-walled carbon nanotubes as the spring elements. Through
atomic-force-microscope force-distance measurements we are able to apply
torsional strains to the nanotubes and measure their torsional spring constants
and effective shear moduli. We find that the effective shear moduli cover a
broad range, with the largest values near the theoretically predicted value.
The data also suggest that the nanotubes are stiffened by repeated flexing.Comment: 4 page
Mn Interstitial Diffusion in (Ga,Mn)As
We present a combined theoretical and experimental study of the ferromagnetic
semiconductor (Ga,Mn)As which explains the remarkably large changes observed on
low temperature annealing. Careful control of the annealing conditions allows
us to obtain samples with ferromagnetic transition temperatures up to 159 K. Ab
initio calculations, and resistivity measurements during annealing, show that
the observed changes are due to out-diffusion of Mn interstitials towards the
surface, governed by an energy barrier of about 0.7-0.8 eV. The Mn interstitial
is a double donor resulting in compensation of charge carriers and suppression
of ferromagnetism. Electric fields induced by high concentrations of
substitutional Mn acceptors have a significant effect on the diffusion.Comment: 5 pages, 4 figures, submitted to Physical Review Letter
SO2 AND ASH VOLCANIC PLUME RETRIEVALS FROM THE 24 NOVEMBER 2006 Mt. ETNA ERUPTION USING MSG-SEVIRI DATA: SO2 VALIDATION AND ASH CORRECTION PROCEDURE
Estimation of the daily trend of sulfur dioxide and ash from the thermal infrared measurements of the Spin Enhanced Visible and Infrared Imager (SEVIRI), on board the Meteosat Second Generation (MSG) geosynchronous satellite, has been carried out. The SO2 retrieval is validated vicariously by using satellite sensors and with ground measurements. The 24 November 2006 tropospheric eruption of Etna volcano is used as a test case. MSG-SEVIRI is an optical imaging radiometer characterized by 12 spectral channels, a high temporal resolution (one image every 15 minutes), and a 10 km2 footprint. The instrument’s spectral range includes the 7.3 and 8.7 mm bands (channels 6 and 7) used for SO2 retrieval and the 10.8 and 12.0 mm (channels 9 and 10) split window bands used for ash detection and retrievals. The SO2 columnar abundance and ash are retrieved simultaneously by means of a Look-Up Table least squares fit procedure for SO2 and using a Brightness Temperature Difference algorithm for ash. The SO2 retrievals obtained using different satellite sensors such as AIRS and MODIS have been carried out and compared with SEVIRI estimations. The results were validated using the permanent mini-DOAS ground system network (FLAME) installed and operated by INGV on Mt. Etna. Results show that the simultaneous presence of SO2 and ash in a volcanic plume yields a significant error in the SO2 columnar abundance retrieval in multispectral Thermal Infrared (TIR) data. The ash plume particles with high effective radius (from 1 to 10 mm) reduce the top of atmosphere radiance in the entire TIR spectral range, including the channels used for the SO2 retrieval. The net effect is a significant SO2 overestimation. To take this effect into account a novel ash correction procedure is presented and applied to the retrieval
Draft Genome Sequence of Antarctic Methanogen Enriched from Dry Valley Permafrost
A genomic reconstruction belonging to the genus Methanosarcina was assembled from metagenomic data from a methane-producing enrichment of Antarctic permafrost. This is the first methanogen genome reported from permafrost of the Dry Valleys and can help shed light on future climate-affected methane dynamics
Structure and stability of finite gold nanowires
Finite gold nanowires containing less than 1000 atoms are studied using the
molecular dynamics simulation method and embedded atom potential. Nanowires
with the face-centered cubic structure and the (111) oriented cross-section are
prepared at T=0 K. After annealing and quenching the structure and vibrational
properties of nanowires are studied at room temperature. Several of these
nanowires form multi-walled structures of lasting stability. They consist of
concentrical cylindrical sheets and resemble multi-walled carbon nanotubes.
Vibrations are investigated by diagonalization of the dynamical matrix. It was
found that several percents of vibrational modes are unstable because of
uncompleted restructuring of initial fcc nanowires.Comment: 4 figures in gif forma
Phonon engineering in nanostructures: Controlling interfacial thermal resistance in multilayer-graphene/dielectric heterojunctions
Article discussing phonon engineering in nanostructures and controlling interfacial thermal resistance in multilayer-graphene/dielectric heterojunctions
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