Size-dependent structural characteristics and phonon thermal transport in silicon nanoclusters

Hai-Peng Li,Rui-Qin Zhang

doi:10.1063/1.4818591

Abstract

We investigate the size effects on the structures and thermal conductivity of silicon nanoclusters (SiNCs) using molecular dynamics simulations. We demonstrate that as the diameter of the SiNCs increases from 1.80 nm to 3.46 nm, the cluster structure changes from an amorphous state to a crystalline state at 300 K, which is in good agreement with the experimental findings. Our calculated thermal conductivity of the SiNCs shows a size-dependent effect due to the remarkable phonon-boundary scattering and can be about three orders of magnitude lower than that of bulk Si.

Highlights

Nanoclusters/nanoparticles have attracted increasing attention in innovative technology due to their unique properties, which are different from those of bulk materials
We investigate the size effects on the structures and thermal conductivity of silicon nanoclusters (SiNCs) using molecular dynamics simulations
We demonstrate that as the diameter of the SiNCs increases from 1.80 nm to 3.46 nm, the cluster structure changes from an amorphous state to a crystalline state at 300 K, which is in good agreement with the experimental findings

Summary

Introduction

Nanoclusters/nanoparticles have attracted increasing attention in innovative technology due to their unique properties, which are different from those of bulk materials. Silicon nanoclusters (SiNCs) have shown excellent promise as a candidate for applications in optoelectronic devices, biological labeling, and solar energy conversion.[1,2,3,4] When their size approaches the nanometer scale, their properties can be considerably altered due to the size and quantum confinement effects which play an important role in determining the materials’ electronic and optical properties. Recent experimental and theoretical studies have found that as the SiNCs size is reduced to several nanometers, the photoluminescence spectrum shifts from the red to the green wavelengths. This indicates that the poor optical characteristics of Si, which result from indirect band structure, can be improved by reducing the particle size to single-nanometer scales.[5]. Compared with the studies conducted on their electronic and optical properties, the study of the thermal conductivity of semiconductor nanoclusters/nanoparticles requires much more effort.[10,11]

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