216 research outputs found
Conductance properties of rough quantum wires with colored surface disorder
Effects of correlated disorder on wave localization have attracted
considerable interest. Motivated by the importance of studies of quantum
transport in rough nanowires, here we examine how colored surface roughness
impacts the conductance of two-dimensional quantum waveguides, using direct
scattering calculations based on the reaction matrix approach. The
computational results are analyzed in connection with a theoretical relation
between the localization length and the structure factor of correlated
disorder. We also examine and discuss several cases that have not been treated
theoretically or are beyond the validity regime of available theories. Results
indicate that conductance properties of quantum wires are controllable via
colored surface disorder.Comment: 19 pages, 7 figure
Diffusive Transport in Quasi-2D and Quasi-1D Electron Systems
Quantum-confined semiconductor structures are the cornerstone of modern-day
electronics. Spatial confinement in these structures leads to formation of
discrete low-dimensional subbands. At room temperature, carriers transfer among
different states due to efficient scattering with phonons, charged impurities,
surface roughness and other electrons, so transport is scattering-limited
(diffusive) and well described by the Boltzmann transport equation. In this
review, we present the theoretical framework used for the description and
simulation of diffusive electron transport in quasi-two-dimensional and
quasi-one-dimensional semiconductor structures. Transport in silicon MOSFETs
and nanowires is presented in detail.Comment: Review article, to appear in Journal of Computational and Theoretical
Nanoscienc
Surface decorated silicon nanowires: a route to high-ZT thermoelectrics
Based on atomistic calculations of electron and phonon transport, we propose
to use surface decorated Silicon nanowires (SiNWs) for thermoelectric
applications. Two examples of surface decorations are studied to illustrate the
underlying deas: Nanotrees and alkyl functionalized SiNWs. For both systems we
find, (i) that the phonon conductance is significantly reduced compared to the
electronic conductance leading to high thermoelectric figure of merit, ,
and (ii) for ultra-thin wires surface decoration leads to significantly better
performance than surface disorder.Comment: Accepted for PR
Electron mobility in silicon nanowires
The low-field electron mobility in rectangular silicon nanowire (SiNW)
transistors was computed using a self-consistent Poisson-Schr\"{o}dinger-Monte
Carlo solver. The behavior of the phonon-limited and surface-roughness-limited
components of the mobility was investigated by decreasing the wire width from
30 nm to 8 nm, the width range capturing a crossover between two-dimensional
(2D) and one-dimensional (1D) electron transport. The phonon-limited mobility,
which characterizes transport at low and moderate transverse fields, is found
to decrease with decreasing wire width due to an increase in the
electron-phonon wavefunction overlap. In contrast, the mobility at very high
transverse fields, which is limited by surface roughness scattering, increases
with decreasing wire width due to volume inversion. The importance of acoustic
phonon confinement is also discussed briefly
Ab initio vibrations in nonequilibrium nanowires
We review recent results on electronic and thermal transport in two different
quasi one-dimensional systems: Silicon nanowires (SiNW) and atomic gold chains.
For SiNW's we compute the ballistic electronic and thermal transport properties
on equal footing, allowing us to make quantitative predictions for the
thermoelectric properties, while for the atomic gold chains we evaluate
microscopically the damping of the vibrations, due to the coupling of the chain
atoms to the modes in the bulk contacts. Both approaches are based on a
combination of density-functional theory, and nonequilibrium Green's functions.Comment: 16 pages, to appear in Progress in Nonequilibrium Green's Functions
IV (PNGF4), Eds. M. Bonitz and K. Baltzer, Glasgow, August 200
Improved fluid dynamics similarity, analysis and verification Annual report, 29 Jun. 1965 - 28 Jun. 1966
Fluid mechanics and dynamic reactions in liquid flow, single-phase flow, and two-phase flo
On Landauer vs. Boltzmann and Full Band vs. Effective Mass Evaluation of Thermoelectric Transport Coefficients
The Landauer approach to diffusive transport is mathematically related to the
solution of the Boltzmann transport equation, and expressions for the
thermoelectric parameters in both formalisms are presented. Quantum mechanical
and semiclassical techniques to obtain from a full description of the
bandstructure, E(k), the number of conducting channels in the Landauer approach
or the transport distribution in the Boltzmann solution are developed and
compared. Thermoelectric transport coefficients are evaluated from an atomistic
level, full band description of a crystal. Several example calculations for
representative bulk materials are presented, and the full band results are
related to the more common effective mass formalism. Finally, given a full E(k)
for a crystal, a procedure to extract an accurate, effective mass level
description is presented.Comment: 33 pages, 8 figure
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