Size and Interface Effects on Thermal Conductivity of Superlattices and Periodic Thin-Film Structures

1997 ◽  
Vol 119 (2) ◽  
pp. 220-229 ◽  
Author(s):  
G. Chen
Keyword(s):  
Thin Film ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Amorphous Materials ◽  
High Efficiency ◽  
Interface Roughness ◽  
Atomic Scale ◽  
Diffuse Interface ◽  
Boltzmann Transport ◽  
Diffuse Interfaces

Superlattices consisting of alternating layers of extremely thin films often demonstrate strong quantum size effects that have been utilized to improve conventional devices and develop new ones. The interfaces in these structures also affect their thermophysical properties through reflection and transmission of heat carriers. This work develops models on the effective thermal conductivity of periodic thin-film structures in the parallel direction based on the Boltzmann transport equation. Different interface conditions including specular, diffuse, and partially specular and partially diffuse interfaces, are considered. Results obtained from the partially specular and partially diffuse interface scattering model are in good agreement with experimental data on GaAs/AlAs superlattices. The study shows that the atomic scale interface roughness is the major cause for the measured reduction in the superlattice thermal conductivity. This work also suggests that by controlling interface roughness, the effective thermal conductivity of superlattices made of bulk materials with high thermal conductivities can be reduced to a level comparable to those of amorphous materials, while maintaining high electrical conductivities. This suggestion opens new possibilities in the search of high efficiency thermoelectric materials.

Temperature Dependence of Thermal Conductivity of Amorphous and Crystal Thin Film by Molecular Dynamics Simulation

2007 ◽  
Author(s):  
Zhengxing Huang ◽  
Zhenan Tang ◽  
Suyuan Bai ◽  
Jun Yu
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Thermal Conductivity ◽  
Integrated Circuits ◽  
Temperature Dependence ◽  
Amorphous Materials ◽  
Dynamics Simulation ◽  
Amorphous Sio2 ◽  
Film Boundary ◽  
Different Temperatures

For crystal materials, thermal conductivity (TC) is proportional to T3 at low temperatures and to T−1 at high temperatures. TCs of most amorphous materials decrease with the decreasing temperatures. If a material is thin film, boundary will influence the TC and then influence the temperature dependence. In this paper, we calculate the TC of crystal and amorphous SiO2 thin films, which is a commonly used material in micro devices and Integrated Circuits, by NEMD simulations. The calculation temperatures are from 100K to 700K and the thicknesses are from 2nm to 8nm. TCs of crystal thin films reach their peak values at different temperatures for different thicknesses. The smaller thickness the larger peak values obtained. But for amorphous thin films, the results show that the temperature dependence of thin films is the same as bulk materials and not relative to their thicknesses. The obtained temperature dependence of the thin films is consistent with some previous measurements and the theory predictions.

Theoretical Thermal Conductivity of Periodic Two-Dimensional Nanocomposites

2003 ◽  
Vol 793 ◽  
Author(s):  
Ronggui Yang ◽  
Gang Chen
Keyword(s):  
Thermal Conductivity ◽  
Lattice Thermal Conductivity ◽  
High Efficiency ◽  
Transport Model ◽  
Cell Interaction ◽  
Phonon Transport ◽  
Two Dimensional ◽  
Boltzmann Transport ◽  
Volumetric Fraction ◽  
Strong Function

ABSTRACTA phonon Boltzmann transport model is established to study the lattice thermal conductivity of nanocomposites with nanowires embedded in a host semiconductor material. Special attention has been paid to cell-cell interaction using periodic boundary conditions. The simulation shows that the temperature profiles in nanocomposites are very different from those in conventional composites, due to ballistic phonon transport at nanoscale. The thermal conductivity of periodic 2-D nanocomposites is a strong function of the size of the embedded wires and the volumetric fraction of the constituent materials. At constant volumetric fraction the smaller the wire diameter, the smaller is the thermal conductivity of periodic two-dimensional nanocomposites. For fixed silicon wire dimension, the lower the atomic percentage of germanium, the lower the thermal conductivity of the nanocomposites. The results of this study can be used to direct the development of high efficiency thermoelectric materials.

Size Effect on the Thermal Conductivity of High-Tc Thin-Film Superconductors

1990 ◽  
Vol 112 (4) ◽  
pp. 872-881 ◽  
Author(s):  
M. I. Flik ◽  
C. L. Tien
Keyword(s):  
Thin Film ◽  
Thermal Conductivity ◽  
Size Effect ◽  
Mean Free Path ◽  
Boltzmann Transport ◽  
Simple Method ◽  
High Tc ◽  
Theory Approximation ◽  
Lead Films ◽  
Reported Data

Using the kinetic theory approximation and reported data, this study shows that at low temperatures, the phonon mean free path in polycrystalline ceramic YBa2Cu3O7 can be of the order of the thickness of thin-film superconductors. In this case, boundary scattering reduces the thermal conductivity with decreasing film thickness. A simple method accounts for the size effect on conduction in thin films. This analysis rests solely on geometric arguments and does not consider the effect of grain boundaries. For conduction along the film, this model approximates well an analytical solution of the Boltzmann transport equation, and is in good agreement with experimental data for thin lead films. The model is also employed to analyze the size effect on conduction across the film and the influence of anisotropy.

Thermal Transport in Novel Silicon Transistors

2004 ◽  
Author(s):  
Keivan Etessam-Yazdani ◽  
Wenjun Liu ◽  
Yizhang Yang ◽  
Mehdi Asheghi
Keyword(s):  
Thermal Conductivity ◽  
Semiconductor Device ◽  
Silicon Layer ◽  
Phonon Transport ◽  
Interface Roughness ◽  
Strained Silicon ◽  
Boltzmann Transport ◽  
Strained Si ◽  
Thin Silicon ◽  
The Impact

This manuscript investigates the relevance and impact of nanoscale thermal phenomena in the state-of-the-art semiconductor device technologies such as: silicon-on-insulator (SOI), strained silicon, and tri-gate CMOS transistors. The experimental data and predictions for thin silicon layer thermal conductivity and the solutions of the Boltzmann transport equations (BTE) for phonon transport in strained-Si/Ge bi-layer configuration are used to estimate the thermal resistance of the SOI, tri-gate, and strained-silicon-on-SiGe-on-insulator (SGOI) transistors, respectively. In particular, the impact of SiGe underlayer and interface roughness on the lateral thermal conductivity of the silicon layer at room temperature is investigated. In order to avoid the complexity of the BTE for predictions of the temperature distribution, Lumped Analytical (LA) models are introduced that are simple to implement and also adequate enough to capture the sub-continuum effects. It is concluded that the SOI, SGOI and tri-gate transistors are all susceptible to self-heating for very thin silicon device layers.

Monte Carlo Simulation of the Thermal Conductivity and Phonon Transport in Nanocomposites

2005 ◽  
Author(s):  
Ming-Shan Jeng ◽  
Ronggui Yang ◽  
David Song ◽  
Gang Chen
Keyword(s):  
Thermal Conductivity ◽  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Silicon Germanium ◽  
High Efficiency ◽  
Three Dimensional ◽  
Simulation Method ◽  
Phonon Transport ◽  
Boltzmann Transport ◽  
Nanoparticle Composites

This paper presents a Monte Carlo simulation scheme to study the phonon transport and thermal conductivity of nanocomposites. Special attention has been paid to the implementation of periodic boundary condition in Monte Carlo simulation. The scheme is applied to study the thermal conductivity of silicon germanium (Si-Ge) nanocomposites, which are of great interest for high efficiency thermoelectric material development. The Monte Carlo simulation was first validated by successfully reproducing the results of (two dimensional) nanowire composites using the deterministic solution of the phonon Boltzmann transport equation and the experimental thermal conductivity of bulk germanium, and then the validated simulation method was used to study (three dimensional) nanoparticle composites, where Si nanoparticles are embedded in Ge host. The size effects of phonon transport in nanoparticle composites were studied and the results show that the thermal conductivity of nanoparticle composites can be lower than alloy value. It was found that randomly distributed nanopaticles in nanocomposites rendered the thermal conductivity values close to that of periodic aligned patterns.

Phonon transport characteristics across silicon thin film pair: Presence of a gap between the films

2015 ◽  
Vol 40 (3) ◽  
Author(s):  
Haider Ali ◽  
Bekir S. Yilbas
Keyword(s):  
Thin Film ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Temperature Difference ◽  
Radiation Heat Transfer ◽  
Phonon Transport ◽  
Radiative Energy ◽  
Gap Size ◽  
Boltzmann Transport ◽  
Silicon Thin Film

AbstractPhonon transport across silicon thin film pair with minute gap (Casimir limit) between the films is studied. Phonon transport characteristics across the gap are examined for various gap sizes, and the transient solution of the frequency-dependent Boltzmann transport equation is presented according to relevant boundary conditions incorporating the gap between the film pair. Since the gap size is minute (Casimir limit), the radiative energy transport between the edges of the film pair is incorporated. In addition, phonon transmission and reflection is introduced at the gap edges, thus satisfying energy conservation. The thermal conductivity predicted is validated through experimental data reported in the open literature. Predicted thermal conductivity data agree well with the experimental data reported in the open literature. Increasing gap size alters the phonon transport characteristics across the film pair. Increasing gap size enhances temperature difference between the edges of the gap; in which case, the effect of phonon transmittance is more significant on the temperature difference than that corresponding to the radiation heat transfer due to Casimir limit.

Lattice Boltzmann Modeling of the Effective Thermal Conductivity for Complex Structured Multiphase Building Materials

2015 ◽  
Vol 1119 ◽  
pp. 694-699 ◽  
Author(s):  
Mazhar Hussain ◽  
Shakeel Ahmad ◽  
Wen Quan Tao
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Lattice Boltzmann ◽  
Building Materials ◽  
Present Model ◽  
High Efficiency ◽  
Theoretical Models ◽  
Random Generation ◽  
Proposed Model ◽  
Experimental Values

The effective thermal conductivity is an important parameter used to predict the thermal performance analysis of complex structured porous building materials. The observation of porous structure of building materials on REV (representative elementary volume) scale showed that pores can be classified into meso and macro pores. In contrast to the traditional models usually used for the (macro-meso) pore connection , a new numerical random generation macro-meso pores (RGMMP) method, based on geometrical and morphological information acquired from measurements or experimental calculations, is proposed here. Along with proposed structure generating tool RGMMP a high efficiency LBM, characterized with the energy conservation and appropriate boundary conditions at numerous interfaces in the complex system, for the solution of the governing equation is described which yields a powerful numerical tool to obtain accurate solutions. Then present model is validated with some theoretical and experimental values of effective thermal conductivity of typical building materials. The comparison of present model and experimental results shows that the proposed model agrees much better with the experimental data than the traditional theoretical models. Therefore, the present model is not limited to the described building materials but can also be used for predicting the effective thermal conductivity of any type of complex structured building materials.

Molecular Dynamics Simulations of Heat Conduction in Nano-Structured Silicon

2007 ◽  
Author(s):  
Koji Miyazaki ◽  
Yoshizumi Iida ◽  
Daisuke Nagai ◽  
Hiroshi Tsukamoto
Keyword(s):  
Thin Film ◽  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Heat Conduction ◽  
Molecular Dynamics Simulations ◽  
Atomic Scale ◽  
Dynamics Simulation ◽  
Phonon Modes ◽  
Dynamics Simulations ◽  
Si Thin Film

We carried out molecular dynamics simulations (MD) of heat conduction in Si thin film and Si films with a nano-hole to represent the nano-structure, in order to investigate the mechanism of the thermal conductivity reduction of nano-structured materials. The Stillinger-Weber potential is used in this study. Different temperatures are applied at the both sides of boundaries of the calculation domain in the z-direction, and periodic boundary conditions are applied in the x and y directions. The calculated temperature profile of a Si thin film of 10.86nm thickness is compared to that calculated by using the phonon Boltzmann transport equation (BTE). These agreed reasonably well with each other, and the phonon mean free path of Si is estimated to be several tens of nanometers. Molecular dynamics simulation of Si at the uniform temperature of 800K is also carried out. Phonon dispersion curves are calculated by using the time-space 2D Fourier transform. The phonon modes at high frequency are not present in nano-structures of Si. We discuss the mechanism of the reduction of the thermal conductivity of nano-structured material on the atomic scale.

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