Thermal conductivity of silicene from first-principles

Abstract

Silicene, as a graphene-like two-dimensional material, now receives exceptional attention of a wide community of scientists and engineers beyond graphene. Despite extensive study on its electric property, little research has been done to accurately calculate the phonon transport of silicene so far. In this paper, thermal conductivity of monolayer silicene is predicted from first-principles method. At 300 K, the thermal conductivity of monolayer silicene is found to be 9.4 W/mK and much smaller than bulk silicon. The contributions from in-plane and out-of-plane vibrations to thermal conductivity are quantified, and the out-of-plane vibration contributes less than 10% of the overall thermal conductivity, which is different from the results of the similar studies on graphene. The difference is explained by the presence of small buckling, which breaks the reflectional symmetry of the structure. The flexural modes are thus not purely out-of-plane vibration and have strong scattering with other modes.

Highly anisotropic thermal conductivity of arsenene: Anab initiostudy

“…However, this contribution decreases as the temperature increases and reaches 7.8% (armchair direction) for temperatures above 300 K. This is in contrast to the case of graphene where the ZA modes provide the main contribution to heat conduction 15 . Due to the special selection rules of phonon scattering in graphene, the ZA mode has a relatively large relaxation time compared to other phonon modes 15 , while due to the puckered structure of arsenene, similar to silicene and phosphorene 16,18 , the hexagonal symmetry of graphene is broken, resulting in larger scattering rates and shorter relaxation times of the ZA modes at high temperatures. The contribution of the ZA modes remains however substantial and roughly equivalent to that of the TA modes in the zigzag direction, while it drops below 10% in the armchair direction.…”

“…Thermal transport in 2D materials has recently attracted the attention of the scientific community, as anomalous heat conduction has been predicted to occur in systems with reduced dimensionality 14 . Phononic properties and thermal conductivity vary significantly from one 2D system to another [15][16][17][18] . For example, silicene has a buckled structure and a lower thermal conductivity 19,20 compared to graphene 12,21,22 .…”

“…The phonon bands exhibit two acoustic modes, a longitudinal one (LA) and an in-plane transverse one (TA), with linear dispersion (ω ∝ q) for q → 0, and an out-of-plane flexure mode (ZA) with quadratic dispersion in the long wavelength limit, which is a general feature of 2D membranes 36 and have been characterized in graphene 15,37 , silicene 16,38 , hBN 39 , MoS 2 40 and ultra thin silicon membranes 41,42 . Flexural modes have a major role in contributing to the thermal conductivity of graphene, both as carriers 15 and as scatterers 43 .…”

Phonon thermal conduction in novel 2D materials

“…Unlike graphene in which all carbon atoms form honey-cone structures within a flat plane, silicon atoms in silicone show a buckled structure, resulting in unique thermal transports fundamentally differing from that in other 2D materials, namely (a) longitudinal and transverse acoustic phonons dominate the thermal transports and the acoustic out-of-plane phonon modes only have less than 10% contributions to the total thermal conductivity [114][115][116][117]; (b) thermal conductivity increases dramatically with tensile strain due to enhancement in acoustic phonon lifetime [118][119][120]. Unfortunately, no experiment on thermal conductivity in silicene has been reported.…”

Physically founded phonon dispersions of few-layer materials and the case of borophene

“…[13][14][15] It is therefore surprising that no consensus exists as to whether unstrained few-layer systems should always display one flexural phonon branch with quadratic phonon dispersion at long wavelengths, even though this is what elasticity theory predicts. [16] Indeed, many recent abinitio calculations report three linear-dispersion acoustic branches (silicene, [17][18][19] [24]), whereas some other abinitio calculations, and virtually every empirical potential calculation, report one quadratic and two linear acoustic branches (silicene, [25] phosphorene, [26,27] [28]). Arguments have even been given to suggest that in a buckled system the flexural branch dispersion should no longer be quadratic.…”