Tensile Strains Give Rise to Strong Size Effects for Thermal Conductivities of Silicene, Germanene and Stanene

TL;DR

This study uses first principles calculations to explore how tensile strain affects the size-dependent thermal conductivities of silicene, germanene, and stanene, revealing strain-induced tunability and complex phonon transport behaviors.

Contribution

It provides new insights into the size and strain effects on thermal conductivity in buckled 2D materials, highlighting the limitations of single mode relaxation time approximation.

Findings

Silicene's thermal conductivity diverges with size under tensile strain.

Unstrained silicene's room temperature k converges to 19.34 W/m-K at 178 nm.

Strain can increase silicene's k to match bulk silicon levels at 84 μm.

Abstract

Based on first principles calculations and self-consistent solution of linearized Boltzmann-Peierls equation for phonon transport approach within a three-phonon scattering framework, we characterize lattice thermal conductivities k of freestanding silicene, germanene and stanene under different isotropic tensile strains and temperatures. We find a strong size dependence of k for silicene with tensile strain, i.e., divergent k with increasing system size, in contrast, the intrinsic room temperature k for unstrained silicene converges with system size to 19.34 W/m-K by 178 nm. The room temperature k of strained silicene becomes as large as that of bulk silicon by 84 um, indicating the possibility of using strain in silicene to manipulate k for thermal management. The relative contribution to the intrinsic k from out-of-plane acoustic modes is largest for unstrained silicene, about 39% at room temperature. The single mode relaxation time approximation, which works reasonably well for bulk silicon, fails to appropriately describe phonon thermal transport in silicene, germanene and stanene within the temperature range considered. For large samples of silicene, k increases with tensile strain, peaks at about 7% strain and then decreases with further strain. In germanene and stanene increasing strain hardens and stabilizes long wavelength out-of-plane acoustic phonons, and leads to similar k behaviors to those of silicene. These findings further our understanding of phonon dynamics in group-IV buckled monolayers and may guide transfer and fabrication techniques of these freestanding samples and engineering k by size and strain for applications of thermal management and thermoelectricity.