A NEMD Study of the Thermal Conductivity and Surface Roughness of Silicon Thin Films

2008 ◽  
Author(s):  
Tai-Ming Chang ◽  
Chien-Chou Weng ◽  
Mei-Jiau Huang
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Surface Roughness ◽  
Surface Potential ◽  
Specular Reflection ◽  
Constant Heat Flux ◽  
Nonequilibrium Molecular Dynamics ◽  
Model Parameters ◽  
Silicon Thin Films ◽  
Three Body

The nonequilibrium molecular dynamics (NEMD) approach is adopted in this work to calculate the in-plane lattice thermal conductivity of Silicon thin films. In the simulation, the Stillinger-Weber (SW) potential is employed to capture both two-body and three-body interactions. The periodic boundary conditions are applied in the in-plane directions of a thin film. An additional surface potential is added to atoms that are near the surfaces. This surface potential imposes a force normal to the plane to prevent atoms from evaporation. A constant heat flux is generated by injecting energy into the system somewhere and withdrawing energy somewhere else via the velocity rescaling method. After a sufficiently long simulation time, the time-averaged temperature distribution is calculated and then the thermal conductivity can be obtained by the Fourier’s law. When the average temperature of the system is lower than the Debye temperature (θD = 645 K for Si), quantum corrections to both the MD temperature and the thermal conductivity are carried out. To speed up the computation, the present MD tool is parallelized based on a spatial decomposition technique. In this study, we attempt to investigate the relationship among the model parameters of the surface potential, the surface roughness, and the specular reflection fraction at the boundary that is often used in many theoretical studies.

Monte Carlo Study of Phonon Heat Conduction in Silicon Thin Films Including Contributions of Optical Phonons

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Arpit Mittal ◽  
Sandip Mazumder
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Monte Carlo ◽  
Heat Conduction ◽  
Phonon Scattering ◽  
Computational Domain ◽  
Optical Phonons ◽  
Phonon Modes ◽  
Silicon Thin Film ◽  
Silicon Thin Films

Abstract The Monte Carlo method has found prolific use in the solution of the Boltzmann transport equation for phonons for the prediction of nonequilibrium heat conduction in crystalline thin films. This paper contributes to the state-of-the-art by performing a systematic study of the role of the various phonon modes on thermal conductivity predictions, in particular, optical phonons. A procedure to calculate three-phonon scattering time-scales with the inclusion of optical phonons is described and implemented. The roles of various phonon modes are assessed. It is found that transverse acoustic (TA) phonons are the primary carriers of energy at low temperatures. At high temperatures (T>200 K), longitudinal acoustic (LA) phonons carry more energy than TA phonons. When optical phonons are included, there is a significant change in the amount of energy carried by various phonons modes, especially at room temperature, where optical modes are found to carry about 25% of the energy at steady state in silicon thin films. Most importantly, it is found that inclusion of optical phonons results in better match with experimental observations for silicon thin-film thermal conductivity. The inclusion of optical phonons is found to decrease the thermal conductivity at intermediate temperatures (50–200 K) and to increase it at high temperature (>200 K), especially when the film is thin. The effect of number of stochastic samples, the dimensionality of the computational domain (two-dimensional versus three-dimensional), and the lateral (in-plane) dimension of the film on the statistical accuracy and computational efficiency is systematically studied and elucidated for all temperatures.

Thermal Conductivity of Ordered Mesoporous Silicon Thin Films Made From Magnesium Reduction of Polymer Templated Silica

2011 ◽  
Author(s):  
Jin Fang ◽  
Laurent Pilon ◽  
Chris B. Kang ◽  
Sarah H. Tolbert
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Film Thickness ◽  
Crystalline Silicon ◽  
Average Crystallite Size ◽  
Face Centered Cubic ◽  
Mesoporous Silicon ◽  
X Ray ◽  
Silicon Thin Films ◽  
The Cross

This paper reports the cross-plane thermal conductivity of ordered polycrystalline mesoporous silicon thin films between 30 and 320 K. The films were produced by a combination of evaporation induced self-assembly (EISA) of mesoporous silica followed by magnesium reduction. The periodic ordering of pores in mesoporous silicon was characterized by a combination of 1D X-ray diffraction, 2D small angle X-ray scattering, and direct SEM imaging. The average crystallite size, porosity, and film thickness were about 13–18 nm, 25–35%, and 140–260 nm, respectively. The pores were arranged in a face-centered cubic lattice. Finally, the cross-plane thermal conductivity of the meso-porous silicon thin films was measured using the 3ω method. The measured thermal conductivity was about 3 to 5 orders of magnitude smaller than that of the bulk dense crystalline silicon for the temperature range considered. The effects of temperature and film thickness on the thermal conductivity were investigated.

Monte Carlo Study of Phonon Heat Conduction in Silicon Thin Films: Role of Optical Phonons

2009 ◽  
Author(s):  
Arpit Mittal ◽  
Sandip Mazumder
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Monte Carlo ◽  
Heat Conduction ◽  
Optical Phonons ◽  
Boltzmann Transport ◽  
Phonon Modes ◽  
Silicon Thin Film ◽  
Silicon Thin Films

The Monte Carlo (MC) method has found prolific use in the solution of the Boltzmann Transport Equation (BTE) for phonons for the prediction of non-equilibrium heat conduction in crystalline thin films. This paper contributes to the state-of-the-art by performing a systematic study of the role of the various phonon modes on thermal conductivity predictions—in particular, optical phonons. A procedure to calculate scattering time-scales with the inclusion of optical phonons is described and implemented. The roles of various phonon modes are assessed. It is found that Transverse acoustic (TA) phonons are the primary carriers of energy at low temperatures. At high temperatures (T > 200K), longitudinal acoustic (LA) phonons carry more energy than TA phonons. When optical phonons are included, there is a significant change in the amount of energy carried by various phonons modes. At room temperature, optical modes are found to carry about 25% of the energy at steady state in Silicon thin films. Most importantly, inclusion of optical phonons results in better match with experimental observations for Silicon thin-film thermal conductivity.

scholarly journals Size effects on the thermal conductivity of amorphous silicon thin films

2016 ◽  
Vol 93 (14) ◽  
Author(s):  
Jeffrey L. Braun ◽  
Christopher H. Baker ◽  
Ashutosh Giri ◽  
Mirza Elahi ◽  
Kateryna Artyushkova ◽  
...  
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Amorphous Silicon ◽  
Size Effects ◽  
Silicon Thin Films
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