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.

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 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.

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.

scholarly journals Ballistic Heat Transport in Nanocomposite: The Role of the Shape and Interconnection of Nanoinclusions

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1982
Author(s):  
Paul Desmarchelier ◽  
Alice Carré ◽  
Konstantinos Termentzidis ◽  
Anne Tanguy
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Free Path ◽  
Mean Free Path ◽  
Strong Increase ◽  
Moderate Increase ◽  
Energy Propagation ◽  
The Mean ◽  
Dynamics Simulations

In this article, the effect on the vibrational and thermal properties of gradually interconnected nanoinclusions embedded in an amorphous silicon matrix is studied using molecular dynamics simulations. The nanoinclusion arrangement ranges from an aligned sphere array to an interconnected mesh of nanowires. Wave-packet simulations scanning different polarizations and frequencies reveal that the interconnection of the nanoinclusions at constant volume fraction induces a strong increase of the mean free path of high frequency phonons, but does not affect the energy diffusivity. The mean free path and energy diffusivity are then used to estimate the thermal conductivity, showing an enhancement of the effective thermal conductivity due to the existence of crystalline structural interconnections. This enhancement is dominated by the ballistic transport of phonons. Equilibrium molecular dynamics simulations confirm the tendency, although less markedly. This leads to the observation that coherent energy propagation with a moderate increase of the thermal conductivity is possible. These findings could be useful for energy harvesting applications, thermal management or for mechanical information processing.

Experiments on the flow of heat in liquid helium below 0.7 °K

1958 ◽  
Vol 246 (1246) ◽  
pp. 390-405 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Liquid Helium ◽  
Free Path ◽  
Empirical Relation ◽  
Mean Free Path ◽  
Series Of Experiments ◽  
The Mean ◽  
Set Up ◽  
Low Pressures ◽  
Measured Thermal Conductivity

A series of experiments has been performed to study the steady flow of heat in liquid helium in tubes of diameter 0.05 to 1.0 cm at temperatures between 0.25 and 0.7 °K. The results are interpreted in terms of the flow of a gas of phonons, in which the mean free path λ varies with temperature, and may be either greater or less than the diameter of the tube d . When λ ≫ d the flow is limited by the scattering of the phonons at the walls, and the effect of the surface has been studied, but when λ ≪ d viscous flow is set up in which the measured thermal conductivity is increased above that for wall scattering. This behaviour is very similar to that observed in the flow of gases at low pressures, and by applying kinetic theory to the problem it can be shown that the mean free path of the phonons characterizing viscosity can be expressed by the empirical relation λ = 3.8 x 10 -3 T -4.3 cm. This result is inconsistent with the temperature dependence of λ as T -9 predicted theoretically by Landau & Khalatnikov (1949).

Thermal Conductance of Nanoparticles: A Study of Phonon Transport in Functionalized Nanodiamond Suspensions

2020 ◽  
Author(s):  
Aaron Bain ◽  
Ethan Languri ◽  
Venkat Padmanabhan ◽  
Jim Davidson ◽  
David Kerns
Keyword(s):  
Thermal Conductivity ◽  
Density Functional ◽  
Transport Theory ◽  
Constitutive Relations ◽  
Thermal Conductance ◽  
Phonon Transport ◽  
Suspension Stability ◽  
Kapitza Resistance ◽  
Conductivity Enhancement ◽  
Underlying Mechanisms

Abstract Nanoparticle additives, with their anomalous thermal conductivity, have attracted attention in research and industry as a novel mode of enhancing the heat transfer mediums. Most studies conducted on nanoparticle suspensions in liquids, pastes, or composites at present have relied on constitutive relations using properties of the bulk substance and of the nanoparticle to explain the effective thermal conductivity. In order to utilize nanoparticles in real world engineering applications, chemical functionalization of the surface of the nanoparticle is frequently employed, either to suspend in liquid applications or to stabilize in arrays. In this study, we have sought to explain the underlying mechanisms of thermal conductivity enhancement taking into consideration the nanoscale effects, such as phonon transport in the nanoparticle coupled with vibrational modes of the surface functional molecules, in order to tailor the functional groups not only for suspension stability but also for minimizing Kapitza resistance at the surface of the nanoparticle. Density functional theory simulations in SIESTA and equilibrium transport theory analysis via GOLLUM2 were used in tandem to evaluate the thermal transport at the nanoparticle to surface ligand junction. By treating the nanoparticle surface and the polymer or acid coating as distinct homogeneous substrates, a model for thermal conductivity becomes more tractable.

Phonon Conduction Normal to Polysilicon Films on Diamond

2013 ◽  
Author(s):  
Jungwan Cho ◽  
Pane C. Chao ◽  
Mehdi Asheghi ◽  
Kenneth E. Goodson
Keyword(s):  
Thermal Conductivity ◽  
Transport Theory ◽  
Phonon Scattering ◽  
Phonon Transport ◽  
Silicon Films ◽  
Silicon Thin Films ◽  
Transmission Electron ◽  
Crystal Films ◽  
Polysilicon Films ◽  
Polycrystalline Silicon Films

Silicon films of thickness near and below one micrometer play a central role in many advanced technologies for computation and energy conversion. Numerous data on the thermal conductivity of silicon thin films are available in the literature, but mainly for the in-plane thermal conductivity of polycrystalline and single-crystal films. Here we use picosecond time-domain thermoreflectance (TDTR), transmission electron microscopy, and phonon transport theory to investigate heat conduction normal to polycrystalline silicon films on diamond substrates. The data agree with predictions that account for the coupled effects of phonon scattering on film boundaries and defects concentrated near grain boundaries. Using the data and the model, we estimate the polysilicon-diamond interface resistance to be 6.5–8 m2 K GW−1.

Significantly enhanced phonon mean free path and thermal conductivity by percolation of silver nanoflowers

2019 ◽  
Vol 21 (5) ◽  
pp. 2453-2462 ◽  
Author(s):  
Daewoo Suh ◽  
Sanghoon Lee ◽  
Chenchen Xu ◽  
Agha Aamir Jan ◽  
Seunghyun Baik
Keyword(s):  
Thermal Conductivity ◽  
Free Path ◽  
Mean Free Path ◽  
Thermal Interface Materials ◽  
Thermal Interface ◽  
Interface Materials ◽  
Polyurethane Matrix ◽  
Percolation Network

A percolation network of silver nanoflowers dramatically increased the thermal conductivity (42.4 W m−1 K−1) in soft polyurethane-matrix thermal interface materials.

Sign in / Sign up

Export Citation Format

Share Document