Reduction of Thermal Conductivity by Nanoscale 3D Phononic Crystal

TL;DR

This study demonstrates that isotopic nanoscale 3D phononic crystals significantly reduce the thermal conductivity of silicon at high temperatures, with size and mass ratio being key factors influencing this effect.

Contribution

It provides new insights into how period length and mass ratio in nanoscale 3D phononic crystals affect thermal conductivity reduction in silicon.

Findings

Thermal conductivity decreases with increasing period length and mass ratio.

Phonon group velocities are reduced in 3D phononic crystals.

Phonon localization and band gaps are observed in spectra.

Abstract

The thermal conductivity of nanostructures needs to be as small as possible so that it will have a greater efficiency for solid-state electricity generation/refrigeration by thermoelectrics. We studied how the period length and the mass ratio affect the thermal conductivity of isotopic nanoscale 3D phononic crystal of Si. Simulation results by equilibrium molecular dynamics show isotopic nanoscale 3D phononic crystal can make a significance reduction on the thermal conductivity of bulk Si at high temperature,1000 K. Size and mass effects are obvious in manipulating thermal conductivity. The thermal conductivity decreases as the period length and mass ratio increases. The phonon dispersion curves show the decrease of group velocities in 3D phononic crystals. The phonon's localization and band gap is clearly shown in spectra of normalized inverse participation ratio in nanoscale 3D phononic crystal structure.