Unexpectedly Large Tunability of Lattice Thermal Conductivity of Monolayer Silicene via Mechanical Strain

TL;DR

This study reveals that monolayer silicene exhibits an unexpectedly large and tunable thermal conductivity under mechanical strain, with a peak at 4% strain due to enhanced phonon lifetimes, challenging prior assumptions about strain insensitivity.

Contribution

It demonstrates the significant and non-monotonic change in silicene's thermal conductivity under strain, highlighting a unique strain-induced phonon lifetime enhancement not observed in other 2D materials.

Findings

Thermal conductivity of silicene increases up to 7.5 times under 4% strain.

The unusual behavior is linked to increased acoustic phonon lifetime.

Strain causes flattening of buckling, affecting phonon dynamics.

Abstract

Strain engineering is one of the most promising and effective routes toward continuously tuning the electronic and optic properties of materials, while thermal properties are generally believed to be insensitive to mechanical strain. In this paper, the strain-dependent thermal conductivity of monolayer silicene under uniform bi-axial tension is computed by solving the phonon Boltzmann transport equation with force constants extracted from first-principles calculations. Unlike the commonly believed understanding that thermal conductivity only slightly decreases with increased tensile strain for bulk materials, it is found that the thermal conductivity of silicene first increases dramatically with strain and then slightly decreases when the applied strain increases further. At a tensile strain of 4%, the highest thermal conductivity is found to be about 7.5 times that of unstrained one. Such an unusual strain dependence is mainly attributed to the dramatic enhancement in the acoustic phonon lifetime. Such enhancement plausibly originates from the flattening of the buckling of the silicene structure upon stretching, which is unique for silicene as compared with other common two-dimensional materials. Our findings offer perspectives of modulating the thermal properties of low-dimensional structures for applications such as thermoelectrics, thermal circuits, and nanoelectronics.