Effect of Hydrogen Passivation on the Thermal Conductivity of Nanoporous Crystalline Silicon: A Molecular Dynamics Study

2012 ◽  
Author(s):  
Jin Fang ◽  
Laurent Pilon
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Phonon Scattering ◽  
Crystalline Silicon ◽  
Scaling Law ◽  
Interfacial Area ◽  
Md Simulations ◽  
Hydrogen Passivation ◽  
Interfacial Area Concentration ◽  
Passivated Silicon

Effect of hydrogen passivation on thermal conductivity of nanoporous crystalline silicon was investigated using equilibrium molecular dynamics (MD) simulations from 500 to 1000 K. The porosity varied from 8% to 38% while the pore diameter ranged from 1.74 to 2.93 nm. Hydrogen passivation of the pore surface was found to reduce thermal conductivity by about 20% at 500 K due to enhanced phonon scattering by the passivated atoms at the nanopore surface. The effect of passivation diminished with increasing temperature. In fact, the phonon density of states at high temperatures was similar for both passivated and unpassivated silicon atoms. Finally, the thermal conductivity k was found to be linearly proportional to (1–1.5fv)/(Ai/4) where fv is the porosity and Ai is the pore interfacial area concentration. This scaling law was previously established for un-passivated silicon using non-equilibrium MD simulations.

Thermal Conductivity of Crystalline Nanoporous Silicon Using Molecular Dynamics Simulations

2011 ◽  
Author(s):  
Jin Fang ◽  
Laurent Pilon
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Effective Thermal Conductivity ◽  
Crystalline Silicon ◽  
Interfacial Area ◽  
Md Simulations ◽  
Nanoporous Silicon ◽  
Vacancy Defects ◽  
Interfacial Area Concentration ◽  
Dynamics Simulations

This study establishes that the effective thermal conductivity keff of crystalline nanoporous silicon is strongly affected not only by the porosity fv and the system’s length Lz but also by the pore interfacial area concentration Ai. The thermal conductivity of crystalline nanoporous silicon was predicted using non-equilibrium molecular dynamics (NEMD) simulations. The Stillinger-Weber potential for silicon was used to simulate the interatomic interactions. Spherical pores organized in a simple cubic lattice were introduced in a crystalline silicon matrix by removing atoms within selected regions of the simulation cell. Effects of the (i) system length ranging from 13 to 130 nm, (ii) pore diameter varying between 1.74 and 5.86 nm, and (iii) porosity ranging from 8% to 38%, on thermal conductivity were investigated. A physics-based model was also developed by combining kinetic theory and the coherent potential approximation. The effective thermal conductivity was proportional to (1–1.5fv) and inversely proportional to the sum (Ai/4+1/Lz). This model was in excellent agreement with the thermal conductivity of nanoporous silicon predicted by MD simulations for spherical pores (present study) as well as for cylindrical pores and vacancy defects reported in the literature. These results will be useful in designing nanostructured materials with desired thermal conductivity by tuning their morphology.

Thermal Transport in Few-Quintuple Bi2Te3 Thin Films and Nanoribbons

2011 ◽  
Author(s):  
Bo Qiu ◽  
Xiulin Ruan
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Temperature Dependence ◽  
Thermal Transport ◽  
Room Temperature ◽  
Phonon Scattering ◽  
Md Simulations ◽  
Boundary Scattering ◽  
Nanoporous Films

In this work, thermal conductivity of perfect and nanoporous few-quintuple Bi2Te3 thin films as well as nanoribbons with perfect and zig-zag edges is investigated using molecular dynamics (MD) simulations with Green-Kubo method. We find minimum thermal conductivity of perfect Bi2Te3 thin films with three quintuple layers (QLs) at room temperature, and we believe it originates from the interplay between inter-quintuple coupling and phonon boundary scattering. Nanoporous films and nanoribbons are studied for additional phonon scattering channels in suppressing thermal conductivity. With 5% porosity in Bi2Te3 thin films, the thermal conductivity is found to decrease by a factor of 4–6, depending on temperature, comparing to perfect single QL. For nanoribbons, width and edge shape are found to strongly affect the temperature dependence as well as values of thermal conductivity.

Molecular Dynamics Simulations of Thermal Conductivity of Bi2Te3 Nanowires

2009 ◽  
Author(s):  
Bo Qiu ◽  
Lin Sun ◽  
Xiulin Ruan
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Surface Roughness ◽  
Smooth Surface ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Md Simulations ◽  
Interatomic Potentials ◽  
Phonon Confinement ◽  
Dynamics Simulations

In this paper, by employing the previously developed two-body interatomic potentials for bismuth telluride, molecular dynamics (MD) simulations are used to describe the thermoelectric properties, namely the lattice thermal conductivity, of Bi2Te3 nanowires. Cylindrical nanowires with both smooth surface and sawtooth surface roughness are studied, aiming at revealing the effects of phonon confinement in 1-D structures, phonon boundary scatterings and surface roughness on the lattice thermal conductivity of Bi2Te3 nanowires. In the end, the influence of various phonon scattering mechanisms on the nanostructures under study are summarized, possible paths to reduce lattice thermal conductivity in nanostructured Bi2Te3, which is favorable for enhancing thermoelectric performance, are pointed out.

A Molecular Dynamics Study of Thermal Conductivity in Nanocomposites via the Phonon Wave Packet Method

2009 ◽  
Author(s):  
Zhiting Tian ◽  
Sang Kim ◽  
Ying Sun ◽  
Bruce White
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Wave Packet ◽  
Molecular Dynamics Simulations ◽  
Phonon Scattering ◽  
Flow Direction ◽  
Normal Incidence ◽  
Material Interfaces ◽  
Non Equilibrium Molecular Dynamics ◽  
Dynamics Simulations

The phonon wave packet technique is used in conjunction with the molecular dynamics simulations to directly observe phonon scattering at material interfaces. The phonon transmission coefficient of nanocomposites is examined as a function of the defect size, thin film thickness, orientation of interface to the heat flow direction. To generalize the results based on phonons in a narrow frequency range and at normal incidence, the effective thermal conductivity of the same nanocomposite structure is calculated using non-equilibrium molecular dynamics simulations for model nanocomposites formed by two mass-mismatched Ar-like solids and heterogeneous Si-SiCO2 systems. The results are compared with the modified effective medium formulation for nanocomposites.

Analysis of Heat Conduction in Silicon Using Molecular Dynamics Simulations

2006 ◽  
Author(s):  
Asegun S. Henry ◽  
Gang Chen
Keyword(s):  
Molecular Dynamics ◽  
Lattice Dynamics ◽  
Crystalline Silicon ◽  
Relaxation Times ◽  
Normal Modes ◽  
Md Simulations ◽  
Dynamics Simulations ◽  
Technological Significance ◽  
Fitting Parameters ◽  
Phonon Properties

Silicon's material properties, have been studied extensively because of its technological significance in a variety of industries, including microelectronics. Yet, questions surrounding the phonon relaxation times in silicon continue to linger.1,2 Previous theoretical works3-5 have generated qualitative expressions for phonon relaxation times, however these approaches require fitting parameters that cannot be determined reliably. This paper first discusses implementation issues associated with using the Green-Kubo method in molecular dynamics (MD) simulations. We compare various techniques used in similar works and discusses several implementation issues that have arisen in the literature. We then describe an alternative procedure for analyzing the normal modes of a crystal to extract phonon relaxation times. As an example material we study bulk crystalline silicon using equilibrium MD simulations and lattice dynamics. The environment dependent interatomic potential6 is used to model the interactions and frequency dependent phonon properties are extracted from the MD simulations.

scholarly journals Ultra-low Thermal Conductivity in Si/Ge Hierarchical Superlattice Nanowire

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Xin Mu ◽  
Lili Wang ◽  
Xueming Yang ◽  
Pu Zhang ◽  
Albert C. To ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Silicon Germanium ◽  
Phonon Scattering ◽  
Low Thermal Conductivity ◽  
Structural Hierarchy ◽  
Si Nanowire ◽  
Hierarchical Structuring ◽  
Simulation Results ◽  
Dynamics Simulations

Abstract Due to interfacial phonon scattering and nanoscale size effect, silicon/germanium (Si/Ge) superlattice nanowire (SNW) can have very low thermal conductivity, which is very attractive for thermoelectrics. In this paper, we demonstrate using molecular dynamics simulations that the already low thermal conductivity of Si/Ge SNW can be further reduced by introducing hierarchical structure to form Si/Ge hierarchical superlattice nanowire (H-SNW). The structural hierarchy introduces defects to disrupt the periodicity of regular SNW and scatters coherent phonons, which are the key contributors to thermal transport in regular SNW. Our simulation results show that periodically arranged defects in Si/Ge H-SNW lead to a ~38% reduction of the already low thermal conductivity of regular Si/Ge SNW. By randomizing the arrangement of defects and imposing additional surface complexities to enhance phonon scattering, further reduction in thermal conductivity can be achieved. Compared to pure Si nanowire, the thermal conductivity reduction of Si/Ge H-SNW can be as large as ~95%. It is concluded that the hierarchical structuring is an effective way of reducing thermal conductivity significantly in SNW, which can be a promising path for improving the efficiency of Si/Ge-based SNW thermoelectrics.

Mechanism of Thermal Conductivity Reduction From Suspended to Supported Graphene: A Quantitative Spectral Analysis of Phonon Scattering

2011 ◽  
Author(s):  
Bo Qiu ◽  
Xiulin Ruan
Keyword(s):  
Thermal Conductivity ◽  
Spectral Analysis ◽  
Phonon Scattering ◽  
Md Simulations ◽  
Mean Free Path ◽  
Spectral Energy ◽  
Phonon Modes ◽  
Suspended Graphene ◽  
Out Of Plane ◽  
Predicted Values

In this work, we perform molecular dynamics (MD) simulations together with phonon spectral analysis to predict the thermal conductivity of both suspended and supported graphene. We quantitatively address the relative importance of different types of phonon in thermal transport and explain why thermal conductivity is significantly reduced in supported graphene compared to that in suspended graphene. Within the framework of equilibrium MD, we perform spectral energy density analysis to obtain the phonon mean free path of each individual phonon mode. The contribution of each mode to thermal conductivity is then calculated and summed to obtain the lattice thermal conductivity in the temperature range 300–650 K. Our predicted values and temperature dependence for both suspended and supported graphene agree with experimental data well. In contrast to prior studies, our results suggest that the contribution from out-of-plane acoustic (ZA) branch to thermal conductivity is around 25–30% in suspended graphene at room temperature. The thermal conductivity of supported graphene is predicted to be largely reduced, which is consistent with experimental observations. Such reduction is shown to be due to stronger scattering of all phonon modes rather than only the ZA mode in the presence of the substrate.

Study of the thermal conductivity of a metal-coated multi-walled carbon nanotube using molecular dynamics atomistic simulations

MRS Advances ◽  
2019 ◽  
Vol 4 (08) ◽  
pp. 507-513 ◽  
Author(s):  
Dinesh Bommidi ◽  
Ravindra Sunil Dhumal ◽  
Iman Salehinia
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Carbon Nanotube ◽  
Phonon Scattering ◽  
Metal Coating ◽  
Atomistic Simulations ◽  
Multi Walled Carbon Nanotube

ABSTRACTThermal conductivity of a nickel-coated tri-wall carbon nanotube was studied using molecular dynamics where both the phonon and electron contributions were considered. Simulations predicted a significant effect of the metal coating on the thermal conductivity, i.e. 50% decrease for 1.2 nm of Ni coating. However, the decreasing rate of the thermal conductivity is minuscule for the metal thicker than 1.6 nm. The smaller thermal conductivity of the metal coating, phonon scattering at the interface, and less impacted heat transfer on the inner tubes of the carbon nanotube rationalized the observed trends.

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