Thermal conductivity of silicene calculated using an optimized Stillinger-Weber potential

Abstract

Silicene, the silicon-based counterpart of graphene with a two-dimensional honeycomb lattice, has attracted tremendous interest both theoretically and experimentally due to its significant potential industrial applications. From the aspect of theoretical study, the widely used classical molecular dynamics simulation is an appropriate way to investigate the transport phenomena and mechanisms in nanostructures such as silicene. Unfortunately, no available interatomic potential can precisely characterize the unique features of silicene. Here, we optimized the Stillinger-Weber potential parameters specifically for a single-layer Si sheet, which can accurately reproduce the low buckling structure of silicene and the full phonon dispersion curves obtained from ab initio calculations. By performing equilibrium and nonequilibrium molecular dynamics simulations and anharmonic lattice dynamics calculations with the new potential, we reveal that the three methods consistently yield an extremely low thermal conductivity of silicene and a short phonon mean-free path, suggesting silicene as a potential candidate for high-efficiency thermoelectric materials. Moreover, by qualifying the relative contributions of lattice vibrations in different directions, we found that the longitudinal phonon modes dominate the thermal transport in silicene, which is fundamentally different from graphene, despite the similarity of their two-dimensional honeycomb lattices.

On the origin of abnormal phonon transport of graphyne

“…To this end, we followed the method we proposed recently [40] to quantify the relative contributions of longitudinal, transverse, and flexural modes to the total phonon transport. This method, although simple, has been successfully used for explaining the phonon transport mechanism in various nanostructures [41][42][43][44]. The contribution to the total heat flux in the two-dimensional graphyne due to the vibration in a specific direction can be expressed as [40] J left!right;a ¼ À 1 2wd…”

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.…”

Thermomechanical analysis of two-dimensional boron monolayers

“…In fact, two-dimensional out-of-plane modes (ZA) are expected to have a significant contribution to the thermal conductivity both at long and small distances as evinced in the case of graphene 26 (ZA mode contributes roughly 75% of the total thermal conductivity). Å), just to name a few, are greatly responsible for a significant reduction in their thermal conductivities [31][32][33] in proportion to extend of the buckling. The buckling of α-boron sheet (0.14 Å) being very small compared to that of δ 6 boron sheet (0.89 Å), coupled with the binding energy difference between buckled α-boron sheet and flat α-boron sheet 6 (2 meV/atom) being very small compared to the binding energy difference between buckled δ 6 -boron sheet and flat δ 6 -boron sheet 10 (100 meV/atom), suggests that the aforementioned high-T ballistic limit is more likely to apply to α-boron sheet but less likely to apply to δ 6 -boron sheet.…”