Tuning the Anisotropic Thermal Transport in {110}-Silicon Membranes with Surface Resonances.

Keqiang Li,Shiyun Xiong,Sebastian Volz,Wang Zeng,Yajuan Cheng,Maofeng Dou

doi:10.3390/nano12010123

Abstract

Understanding the thermal transport in nanostructures has important applications in fields such as thermoelectric energy conversion, novel computing and heat dissipation. Using non-homogeneous equilibrium molecular dynamic simulations, we studied the thermal transport in pristine and resonant Si membranes bounded with {110} facets. The break of symmetry by surfaces led to the anisotropic thermal transport with the thermal conductivity along the [110]-direction to be 1.78 times larger than that along the [100]-direction in the pristine structure. In the pristine membranes, the mean free path of phonons along both the [100]- and [110]-directions could reach up to ∼100 µm. Such modes with ultra-long MFP could be effectively hindered by surface resonant pillars. As a result, the thermal conductivity was significantly reduced in resonant structures, with 87.0% and 80.8% reductions along the [110]- and [100]-directions, respectively. The thermal transport anisotropy was also reduced, with the ratio decreasing to 1.23. For both the pristine and resonant membranes, the thermal transport was mainly conducted by the in-plane modes. The current work could provide further insights in understanding the thermal transport in thin membranes and resonant structures.

Highlights

Thermal transport engineering plays an important role in many fields, ranging from thermoelectric energy conversion, novel computing with heat and heat dissipation, to heat insulation [1,2,3,4]
Fe is supposed to be much smaller than the inverse of characteristic phonon mean free path (MFP) λ [40]
We examined the length corresponding to 90% of the total thermal conductivity (TC)

Summary

Introduction

Thermal transport engineering plays an important role in many fields, ranging from thermoelectric energy conversion, novel computing with heat and heat dissipation, to heat insulation [1,2,3,4]. Due to boundary scatterings and change in phonon dispersions, the TC of materials at nanoscales differs significantly from the corresponding bulk values. When the boundary scattering dominates the transport, the TC normally decreases with the shrink in size [5,6,7]. The TC usually increases significantly with the reduction in size when phonon dispersion variation is predominant, which is commonly observed in layered materials [8,9]. Such different size-dependent TC provides opportunities for different applications. The remarkable reduction in TC caused by boundary scattering in low dimensional

Methods

Results

Conclusion