1,381 research outputs found
A theory for molecular transport phenomena through thin membranes
Theory for molecular transport phenomena through thin membrane
A Simple Boltzmann Transport Equation for Ballistic to Diffusive Transient Heat Transport
Developing simplified, but accurate, theoretical approaches to treat heat
transport on all length and time scales is needed to further enable scientific
insight and technology innovation. Using a simplified form of the Boltzmann
transport equation (BTE), originally developed for electron transport, we
demonstrate how ballistic phonon effects and finite-velocity propagation are
easily and naturally captured. We show how this approach compares well to the
phonon BTE, and readily handles a full phonon dispersion and energy-dependent
mean-free-path. This study of transient heat transport shows i) how fundamental
temperature jumps at the contacts depend simply on the ballistic thermal
resistance, ii) that phonon transport at early times approach the ballistic
limit in samples of any length, and iii) perceived reductions in heat
conduction, when ballistic effects are present, originate from reductions in
temperature gradient. Importantly, this framework can be recast exactly as the
Cattaneo and hyperbolic heat equations, and we discuss how the key to capturing
ballistic heat effects is to use the correct physical boundary conditions.Comment: 9 pages, 5 figure
Simulation of the Spin Field Effect Transistors: Effects of Tunneling and Spin Relaxation on its Performance
A numerical simulation of spin-dependent quantum transport for a spin field
effect transistor (spinFET) is implemented in a widely used simulator nanoMOS.
This method includes the effect of both spin relaxation in the channel and the
tunneling barrier between the source/drain and the channel. Account for these
factors permits setting more realistic performance limits for the transistor,
especially the magnetoresistance, which is found to be lower compared to
earlier predictions. The interplay between tunneling and spin relaxation is
elucidated by numerical simulation. Insertion of the tunneling barrier leads to
an increased magnetoresistance. Numerical simulations are used to explore the
tunneling barrier design issues.Comment: 31 pages, 14 figures, submitted to Journal of Applied Physic
Simulation of phonon-assisted band-to-band tunneling in carbon nanotube field-effect transistors
Electronic transport in a carbon nanotube (CNT) metal-oxide-semiconductor
field effect transistor (MOSFET) is simulated using the non-equilibrium Green's
functions method with the account of electron-phonon scattering. For MOSFETs,
ambipolar conduction is explained via phonon-assisted band-to-band
(Landau-Zener) tunneling. In comparison to the ballistic case, we show that the
phonon scattering shifts the onset of ambipolar conduction to more positive
gate voltage (thereby increasing the off current). It is found that the
subthreshold swing in ambipolar conduction can be made as steep as 40mV/decade
despite the effect of phonon scattering.Comment: 13 pages, 4 figure
Ballisticity of nanotube FETs: Role of phonon energy and gate bias
We investigate the role of electron-phonon scattering and gate bias in
degrading the drive current of nanotube MOSFETs. Our central results are: (i)
Optical phonon scattering significantly decreases the drive current only when
gate voltage is higher than a well-defined threshold. It means that elastic
scattering mechanisms are most detrimental to nanotube MOSFETs. (ii) For
comparable mean free paths, a lower phonon energy leads to a larger degradation
of drive current. Thus for semiconducting nanowire FETs, the drive current will
be more sensitive than carbon nanotube FETs because of the smaller phonon
energies in semiconductors. (iii) Radial breathing mode phonons cause an
appreciable reduction in drive current.Comment: 16 pages, 1 table, 4 figure
Flight and Wind-tunnel Investigation to Determine the Aileron-vibration Characteristics of 1/4-scale Wing Panels of the Douglas D-558-2 Research Airplane
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