Directional dependence of boundary-scattering mean free path of phonons in germanium and silicon

1979 ◽  
Vol 19 (6) ◽  
pp. 3133-3136 ◽  
Author(s):  
D. P. Singh ◽  
Y. P. Joshi
Keyword(s):  
Free Path ◽  
Mean Free Path ◽  
Boundary Scattering ◽  
Directional Dependence

Electron and Phonon Thermal Conduction in Epitaxial High-Tc Superconducting Films

1993 ◽  
Vol 115 (1) ◽  
pp. 17-25 ◽  
Author(s):  
K. E. Goodson ◽  
M. I. Flik
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Size Effect ◽  
Free Path ◽  
Fluid Model ◽  
Mean Free Path ◽  
Boundary Scattering ◽  
High Tc ◽  
Two Fluid Model ◽  
Electron Mean Free Path

Electrons and phonons are the carriers of heat in the a-b plane of the high-Tc superconductor YBa2Cu3O7. In the absence of boundary scattering, the a-b plane thermal conductivity and the mean free path of each carrier type are calculated as functions of temperature using kinetic theory, the two-fluid model of the superconducting state, and experimental data for the thermal conductivity and electrical resistivity of a single crystal. The reduction by boundary scattering of the effective a-b plane thermal conductivity along an epitaxial YBa2Cu3O7 film is predicted as a function of temperature and film thickness. The size effect on the phonon conductivity dominates over the size effect on the electron conductivity. The predicted electron mean free path is limited by scattering on defects and is in very good agreement with experimental data from infrared spectroscopy.

Thermal Transport Property of Silicon Membranes With Asymmetric Porous Structure

2015 ◽  
Author(s):  
Harutoshi Hagino ◽  
Koji Miyazaki
Keyword(s):  
Thermal Conductivity ◽  
Free Path ◽  
Thermal Conduction ◽  
Transport Theory ◽  
Mean Free Path ◽  
Phonon Transport ◽  
Boundary Scattering ◽  
Rectification Effect ◽  
Thermal Rectification ◽  
Asymmetric Pores

The size effect on thermal conduction due to phonon boundary scattering in films was studied as controlling heat conduction. Thermal rectifier was proposed as a new heat control concept by a ballistic rectifier relies on asymmetric scattering of phonons in asymmetric linear structure. We focus on the thermal rectification effect in membrane with asymmetric pores. We discussed on the thermal rectification effect from the calculation and thermal conductivity measurement of asymmetric structured membrane. Thermal conduction was calculated by using radiation calculation of ANSYS Fluent based on Boltzmann transport theory which is development of equation of phonon radiative transfer from view point of phonon mean free path and boundary scattering condition. In-plane thermal conductivities of free standing membranes with microsized asymmetric pores were measured by periodic laser heating measurement. From the result of calculation, phonons were transition to ballistic transport in the membranes with asymmetric shaped pores and thermal rectification effect was obtained on the condition of specular scattering because of the asymmetric back-scattering of ballistic phonons from asymmetric structure. The thermal rectification effect was increased with decreasing thickness of membrane shorter and shorter than mean free path of phonon. From the result of measurements, we were able to confirm the reduction of thermal conductivity based on ballistic phonon transport theory, but the strong thermal rectification effect was not confirmed.

Thermal conduction in artificial sapphire crystals at low temperatures I. Nearly perfect crystals

1955 ◽  
Vol 231 (1184) ◽  
pp. 130-144 ◽  
Keyword(s):  
Free Path ◽  
Low Temperatures ◽  
Thermal Conduction ◽  
Rough Surfaces ◽  
Mean Free Path ◽  
Boundary Scattering ◽  
Crystal Diameter ◽  
Different Sources

In order to obtain a detailed verification of the theory of thermal conduction in dielectric crystals, measurements have been made on a number of artificial sapphire crystals between 2° and 100° K. In the region of the maximum there are variations in conductivity between crystals from different sources. The highest conductivities measured are about 140 W/cm deg., which suggests that estimates of several hundred watts for the maxima of ideal sapphire crystals are not unreasonable. At sufficiently low temperatures the conductivity of a very perfect, long crystal with rough surfaces is observed, in agreement with Casimir’s theory of boundary scattering, to be proportional to T 3 and to the radius; the phonon mean free path is then nearly equal to the crystal diameter. Imperfect crystals show some anomalous effects. The extension of Casimir’s theory to apply to short specimens has been verified. Perfect crystals with smooth surfaces exhibit some specular reflexion of phonons; a statistical description of the surface is proposed which leads to the observed variation of this effect with temperature and is compatible with the results of interferometric examination of the surface.

Diffusive-Ballistic Heat Transport in Thin Films Using Energy Conserving Dissipative Particle Dynamics

2012 ◽  
Author(s):  
Toru Yamada ◽  
Sina Hamian ◽  
Keunhan Park ◽  
Yutaka Asako ◽  
Mohammad Faghri
Keyword(s):  
Thin Films ◽  
Heat Transport ◽  
Free Path ◽  
Dissipative Particle Dynamics ◽  
Mean Free Path ◽  
Particle Dynamics ◽  
Boundary Scattering ◽  
Solution Domain ◽  
Energy Conserving ◽  
Cutoff Radius

Diffusive-ballistic heat transport in thin films was simulated using energy conserving dissipative particle dynamics (DPDe). The solution domain was considered to be two-dimensional and DPD particles were distributed in the solution domain uniformly under constant temperature boundary conditions at the top and bottom walls and periodic boundary at the side walls. The effects of phonon mean free path was incorporated by its relation to the cutoff radius of energy interaction. This cutoff radius was obtained based on Knudsen number using the existing phonon-boundary scattering models. The simulations for 0.1 < Kn < 10 were conducted with the different modifications of the cutoff radius. The results were presented in form of temperature profile across the thin film and were compared with the semi-analytical solution of the equation of phonon radiative transport (EPRT). The discrepancy of the simulations without the phonon mean free path modification was less than 15% with EPRT. Good agreement with EPRT to within 5% was obtained when the phonon-boundary scattering effects were included.

The thermal conductivity of tin and indium below 1°K

1958 ◽  
Vol 248 (1255) ◽  
pp. 522-538 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Free Path ◽  
Superconducting State ◽  
Size Dependence ◽  
Mean Free Path ◽  
Fermi Velocity ◽  
Boundary Scattering ◽  
Simple Analysis ◽  
Phonon Field ◽  
Size Dependent

An experimental study has been made of some aspects of the thermal conductivity of superconducting tin and indium below 1°K. Experiments at the lowest temperatures, where the thermal conductivity of the lattice is dominant, and for tin varies as T 3 , have been mainly directed towards studying the size effect in the conductivity due to the scattering of phonons at the specimen surface. Electropolishing tin has been found to increase the thermal conductivity considerably; a simple analysis of the results shows that almost complete specular reflexion of phonons is attainable. The analysis confirms the existence of an internal scattering of phonons, describable at the lowest temperatures by a temperature-independent mean free path which does not vary when the diameter of the specimen is reduced, but is very sensitive to any damage suffered by the crystal. The lattice conductivity of indium, which is anomalous in having a T 4 rather than a T 3 variation, appears to be limited mainly by internal scattering and it is tentatively suggested that the internal scattering is mainly due to the reradiation from dislocations oscillating in the phonon field. At somewhat higher temperatures (above about 0.7 but below 1°K) the thermal conductivity is predominantly electronic and the results indicate that here too the ‘effective’ electronic mean free path is size-dependent due to boundary scattering. From an analysis of this size-dependence in tin, the ‘intrinsic’ electronic mean free path in the superconducting state is deduced and found to be between ten and thirty times as long as in the normal state. The results suggest also that the electronic velocity in the superconducting state is something like one-third of the Fermi velocity.

Inelastic mean free path and phase-shift determinations in NiO, using EXELFS

1993 ◽  
Vol 3 (7) ◽  
pp. 1649-1659
Author(s):  
Mohammad A. Tafreshi ◽  
Stefan Csillag ◽  
Zou Wei Yuan ◽  
Christian Bohm ◽  
Elisabeth Lefèvre ◽  
...  
Keyword(s):  
Phase Shift ◽  
Free Path ◽  
Mean Free Path ◽  
Inelastic Mean Free Path
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