179 research outputs found
Carbon Nanocone: A Promising Thermal Rectifier
With molecular dynamics simulations, we demonstrate very obvious thermal
rectification in large temperature range from 200 to 400 K in nanocone. We also
observe that the rectification of nanocone does not depend on the length very
sensitively, which is in stark contrast with the nanotube thermal rectifier in
which the rectification decreases dramatically as the length increases. Our
work demonstrates that carbon nanocone is a promising practical phononic
device
Thermal Rectification In Asymmetric Graphene Ribbons
In this paper, heat flux in graphene nano ribbons has been studied by using
molecular dynamics simulations. It is found that the heat flux runs
preferentially along the direction of decreasing width, which demonstrates
significant thermal rectification effect in the asymmetric graphene ribbons.
The dependence of rectification ratio on the vertex angle and the length are
also discussed. Compared to the carbon nanotube based one-dimensional thermal
rectifier, graphene nano ribbons have much higher rectification ratio even in
large scale. Our results demonstrate that asymmetric graphene ribbon might be a
promising structure for practical thermal (phononics) device
A Universal Gauge for Thermal Conductivity of Silicon Nanowires With Different Cross Sectional Geometries
By using molecular dynamics simulations, we study thermal conductivity of
silicon nanowires (SiNWs) with different cross sectional geometries. It is
found that thermal conductivity decreases monotonically with the increase of
surface-to-volume ratio (SVR). More interestingly, a simple universal linear
dependence of thermal conductivity on SVR is observed for SiNWs with modest
cross sectional area (larger than 20 nm^2), regardless of the cross sectional
geometry. As a result, among different shaped SiNWs with the same cross
sectional area, the one with triangular cross section has the lowest thermal
conductivity. Our study provides not only a universal gauge for thermal
conductivity among different cross sectional geometries, but also a designing
guidance to tune thermal conductivity by geometry.Comment: 22 pages, 6 figure
Ballistic magneto-thermal transport in a Heisenberg spin chain at low temperatures
We study ballistic thermal transport in Heisenberg spin chain with
nearest-neighbor ferromagnetic interactions at low temperatures. Explicit
expressions for transmission coefficients are derived for thermal transport in
a periodic spin chain of arbitrary junction length by a spin-wave model. Our
analytical results agree very well with the ones from nonequilibrium Green's
function method. Our study shows that the transmission coefficient oscillates
with the frequency of thermal wave. Moreover, the thermal transmission shows
strong dependence on the intrachain coupling, the length of the spin chain, and
the external magnetic field. The results demonstrate the possibility of
manipulating spin-wave propagation and magnetothermal conductance in the
spin-chain junction by adjusting the intrachain coupling and/or the external
magnetic field.Comment: 6 pages, 7 figure
Molecular Dynamics Simulations of Heat Conduction in Nanostructures: Effect of Heat Bath
We investigate systematically the impacts of heat bath used in molecular
dynamics simulations on heat conduction in nanostructures exemplified by
Silicon Nanowires (SiNWs) and Silicon/Germanium nano junction. It is found that
multiple layers of Nos\'e-Hoover heat bath are required to reduce the
temperature jump at the boundary, while only a single layer of Langevin heat
bath is sufficient to generate a linear temperature profile with small boundary
temperature jump. Moreover, an intermediate value of heat bath parameter is
recommended for both Nos\'e-Hoover and Langevin heat bath in order to achieve
correct temperature profile and thermal conductivity in homogeneous materials.
Furthermore, the thermal rectification ratio in Si/Ge thermal diode depends on
the choice of Nos\'e-Hoover heat bath parameter remarkably, which may lead to
non-physical results. In contrast, Langevin heat bath is recommended because it
can produce consistent results with experiment in large heat bath parameter
range.Comment: 18 pages, 4 figures. This manuscript is accepted for publication in
JPS
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