184 research outputs found
Jahn-Teller Distortions and the Supershell Effect in Metal Nanowires
A stability analysis of metal nanowires shows that a Jahn-Teller deformation
breaking cylindrical symmetry can be energetically favorable, leading to stable
nanowires with elliptic cross sections. The sequence of stable cylindrical and
elliptical nanowires allows for a consistent interpretation of experimental
conductance histograms for alkali metals, including both the shell and
supershell structures. It is predicted that for gold, elliptical nanowires are
even more likely to form since their eccentricity is smaller than for alkali
metals. The existence of certain metastable ``superdeformed'' nanowires is also
predicted
On the Stability and Structural Dynamics of Metal Nanowires
This article presents a brief review of the nanoscale free-electron model,
which provides a continuum description of metal nanostructures. It is argued
that surface and quantum-size effects are the two dominant factors in the
energetics of metal nanowires, and that much of the phenomenology of nanowire
stability and structural dynamics can be understood based on the interplay of
these two competing factors. A linear stability analysis reveals that metal
nanocylinders with certain magic conductance values G=1, 3, 6, 12, 17, 23, 34,
42, 51, 67, 78, 96, ... times the conductance quantum are exceptionally stable.
A nonlinear dynamical simulation of nanowire structural evolution reveals a
universal equilibrium shape consisting of a magic cylinder suspended between
unduloidal contacts. The lifetimes of these metastable structures are also
computed.Comment: 8 pages, 6 figure
Electronic and atomic shell structure in aluminum nanowires
We report experiments on aluminum nanowires in ultra-high vacuum at room
temperature that reveal a periodic spectrum of exceptionally stable structures.
Two "magic" series of stable structures are observed: At low conductance, the
formation of stable nanowires is governed by electronic shell effects whereas
for larger contacts atomic packing dominates. The crossover between the two
regimes is found to be smooth. A detailed comparison of the experimental
results to a theoretical stability analysis indicates that while the main
features of the observed electron-shell structure are similar to those of
alkali and noble metals, a sequence of extremely stable wires plays a unique
role in Aluminum. This series appears isolated in conductance histograms and
can be attributed to "superdeformed" non-axisymmetric nanowires.Comment: 15 pages, 9 figure
Effects of Visual, Seat, and Platform Motion During Flight Simulator Air Transport Pilot Training and Evaluation
Access to affordable and effective flight-simulation training devices (FSTDs) is critical to safely train airline crews in aviating, navigating, communicating, making decisions, and managing flightdeck and crew resources. This paper provides an overview of the Federal Aviation Administration- Volpe Center Flight Simulator Human Factors Program examining the requirements for the qualification and use of FSTDs. We will summarize past research investigating the need for a full hexapod-platform motion system, describe regulatory and industry developments, and report on current activities
Stability of Metal Nanowires at Ultrahigh Current Densities
We develop a generalized grand canonical potential for the ballistic
nonequilibrium electron distribution in a metal nanowire with a finite applied
bias voltage. Coulomb interactions are treated in the self-consistent Hartree
approximation, in order to ensure gauge invariance. Using this formalism, we
investigate the stability and cohesive properties of metallic nanocylinders at
ultrahigh current densities. A linear stability analysis shows that metal
nanowires with certain {\em magic conductance values} can support current
densities up to 10^11 A/cm^2, which would vaporize a macroscopic piece of
metal. This finding is consistent with experimental studies of gold nanowires.
Interestingly, our analysis also reveals the existence of reentrant stability
zones--geometries that are stable only under an applied bias.Comment: 12 pages, 6 figures, version published in PR
Universality in metallic nanocohesion: a quantum chaos approach
Convergent semiclassical trace formulae for the density of states and
cohesive force of a narrow constriction in an electron gas, whose classical
motion is either chaotic or integrable, are derived. It is shown that mode
quantization in a metallic point contact or nanowire leads to universal
oscillations in its cohesive force: the amplitude of the oscillations depends
only on a dimensionless quantum parameter describing the crossover from chaotic
to integrable motion, and is of order 1 nano-Newton, in agreement with recent
experiments. Interestingly, quantum tunneling is shown to be described
quantitatively in terms of the instability of the classical periodic orbits.Comment: corrects spelling of one author name on abstract page (paper is
unchanged
The Escape Problem in a Classical Field Theory With Two Coupled Fields
We introduce and analyze a system of two coupled partial differential
equations with external noise. The equations are constructed to model
transitions of monovalent metallic nanowires with non-axisymmetric intermediate
or end states, but also have more general applicability. They provide a rare
example of a system for which an exact solution of nonuniform stationary states
can be found. We find a transition in activation behavior as the interval
length on which the fields are defined is varied. We discuss several
applications to physical problems.Comment: 24 page
The number of transmission channels through a single-molecule junction
We calculate transmission eigenvalue distributions for Pt-benzene-Pt and
Pt-butadiene-Pt junctions using realistic state-of-the-art many-body
techniques. An effective field theory of interacting -electrons is used to
include screening and van der Waals interactions with the metal electrodes. We
find that the number of dominant transmission channels in a molecular junction
is equal to the degeneracy of the molecular orbital closest to the metal Fermi
level.Comment: 9 pages, 8 figure
From favorable atomic configurations to supershell structures: a new interpretation of conductance histograms
Title: From favorable atomic configurations to supershell structures: a new
interpretation of conductance histograms Authors: A. Hasmy (IVIC), E. Medina
(IVIC), P.A. Serena (CSIC,IVIC) Comments: 7 pages, 3 figures,
cond-mat.anwar.10825 Subj-class: Soft Condensed MatterComment: 7 pages, 3 figuresSubject: fput HMS.tex HMS-FIG1.ps HMS-FIG2.ps
HMS-FIG3.p
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