512 research outputs found
Electron transport through a metal-molecule-metal junction
Molecules of bisthiolterthiophene have been adsorbed on the two facing gold
electrodes of a mechanically controllable break junction in order to form
metal-molecule(s)-metal junctions. Current-voltage (I-V) characteristics have
been recorded at room temperature. Zero bias conductances were measured in the
10-100 nS range and different kinds of non-linear I-V curves with step-like
features were reproducibly obtained. Switching between different kinds of I-V
curves could be induced by varying the distance between the two metallic
electrodes. The experimental results are discussed within the framework of
tunneling transport models explicitly taking into account the discrete nature
of the electronic spectrum of the molecule.Comment: 12 pages, 12 figures to appear in Phys. Rev. B 59(19) 199
Analysis of Multijunction solar cells: Electroluminescence study
This paper describes the principle of the study which is based on electroluminescence to extract the parameters characterizing the recombination centers induced by irradiation in a solar cell. This technique is able to provide direct information on each individual junction constituting the multijonctions. The results are compared with those obtained by electrical methods.This paper describes the principle of the study which is based on electroluminescence to extract the parameters characterizing the recombination centers induced by irradiation in a solar cell. This technique is able to provide direct information on each individual junction constituting the multijonctions. The results are compared with those obtained by electrical methods
First-principles calculation of intrinsic defect formation volumes in silicon
We present an extensive first-principles study of the pressure dependence of
the formation enthalpies of all the know vacancy and self-interstitial
configurations in silicon, in each charge state from -2 through +2. The neutral
vacancy is found to have a formation volume that varies markedly with pressure,
leading to a remarkably large negative value (-0.68 atomic volumes) for the
zero-pressure formation volume of a Frenkel pair (V + I). The interaction of
volume and charge was examined, leading to pressure--Fermi level stability
diagrams of the defects. Finally, we quantify the anisotropic nature of the
lattice relaxation around the neutral defects.Comment: 9 pages, 9 figure
Electron transport through rectifying self-assembled monolayer diodes on silicon: Fermi level pinning at the molecule-metal interface
We report the synthesis and characterization of molecular rectifying diodes
on silicon using sequential grafting of self-assembled monolayers of alkyl
chains bearing a pi group at their outer end (Si/sigma-pi/metal junctions). We
investigate the structure-performance relationships of these molecular devices
and we examine to what extent the nature of the pi end-group (change in the
energy position of their molecular orbitals) drives the properties of these
molecular diodes. For all the pi-groups investigated here, we observe
rectification behavior. These results extend our preliminary work using phenyl
and thiophene groups (S. Lenfant et al., Nano Letters 3, 741 (2003)).The
experimental current-voltage curves are analyzed with a simple analytical
model, from which we extract the energy position of the molecular orbital of
the pi-group in resonance with the Fermi energy of the electrodes. We report
the experimental studies of the band lineup in these silicon/alkyl-pi
conjugated molecule/metal junctions. We conclude that Fermi level pinning at
the pi-group/metal interface is mainly responsible for the observed absence of
dependence of the rectification effect on the nature of the pi-groups, even
though they were chosen to have significant variations in their electronic
molecular orbitalsComment: To be published in J. Phys. Chem.
A Spherical Plasma Dynamo Experiment
We propose a plasma experiment to be used to investigate fundamental
properties of astrophysical dynamos. The highly conducting, fast-flowing plasma
will allow experimenters to explore systems with magnetic Reynolds numbers an
order of magnitude larger than those accessible with liquid-metal experiments.
The plasma is confined using a ring-cusp strategy and subject to a toroidal
differentially rotating outer boundary condition. As proof of principle, we
present magnetohydrodynamic simulations of the proposed experiment. When a von
K\'arm\'an-type boundary condition is specified, and the magnetic Reynolds
number is large enough, dynamo action is observed. At different values of the
magnetic Prandtl and Reynolds numbers the simulations demonstrate either
laminar or turbulent dynamo action
Scaling Law in Carbon Nanotube Electromechanical Devices
We report a method for probing electromechanical properties of multiwalled
carbon nanotubes(CNTs). This method is based on AFM measurements on a doubly
clamped suspended CNT electrostatically deflected by a gate electrode. We
measure the maximum deflection as a function of the applied gate voltage. Data
from different CNTs scale into an universal curve within the experimental
accuracy, in agreement with a continuum model prediction. This method and the
general validity of the scaling law constitute a very useful tool for designing
actuators and in general conducting nanowire-based NEMS.Comment: 12 pages, 4 figures. To be published in Phys. Rev. Let
Measurements of the magnetic field induced by a turbulent flow of liquid metal
Initial results from the Madison Dynamo Experiment provide details of the
inductive response of a turbulent flow of liquid sodium to an applied magnetic
field. The magnetic field structure is reconstructed from both internal and
external measurements. A mean toroidal magnetic field is induced by the flow
when an axial field is applied, thereby demonstrating the omega effect.
Poloidal magnetic flux is expelled from the fluid by the poloidal flow.
Small-scale magnetic field structures are generated by turbulence in the flow.
The resulting magnetic power spectrum exhibits a power-law scaling consistent
with the equipartition of the magnetic field with a turbulent velocity field.
The magnetic power spectrum has an apparent knee at the resistive dissipation
scale. Large-scale eddies in the flow cause significant changes to the
instantaneous flow profile resulting in intermittent bursts of non-axisymmetric
magnetic fields, demonstrating that the transition to a dynamo is not smooth
for a turbulent flow.Comment: 9 pages, 11 figures, invited talk by C. B. Forest at 2005 APS DPP
meeting, resubmitted to Physics of Plasma
Optical properties of metallic (III,Mn)V ferromagnetic semiconductors in the infrared to visible range
We report on a study of the ac conductivity and magneto-optical properties of
metallic ferromagnetic (III,Mn)V semiconductors in the infrared to visible
spectrum. Our analysis is based on the successful kinetic exchange model for
(III,Mn)V ferromagnetic semiconductors. We perform the calculations within the
Kubo formalism and treat the disorder effects pertubatively within the Born
approximation, valid for the metallic regime. We consider an eight-band
Kohn-Luttinger model (six valence bands plus two conduction bands) as well as a
ten-band model with additional dispersionless bands simulating
phenomenologically the upper-mid-gap states induced by antisite and
interstitial impurities. These models qualitatively account for
optical-absorption experiments and predict new features in the mid-infrared
Kerr angle and magnetic-circular-dichroism properties as a function of Mn
concentration and free carrier density.Comment: 10 pages, 7 figures, some typos correcte
Entanglement over global distances via quantum repeaters with satellite links
We study entanglement creation over global distances based on a quantum
repeater architecture that uses low-earth orbit satellites equipped with
entangled photon sources, as well as ground stations equipped with quantum
non-demolition detectors and quantum memories. We show that this approach
allows entanglement creation at viable rates over distances that are
inaccessible via direct transmission through optical fibers or even from very
distant satellites.Comment: 5+3 pages, 3+2 figure
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