Structural, mechanical and thermal properties of twisted bilayer MoS2: First-principles calculations

Abstract

Manipulating interlayer twist angle represents a potent approach for tuning properties of layered two-dimensional crystals. However, limited attention has been given to explore the impact of twist angle on elastic properties. We employ first-principles calculations to investigate how twist angles affect the structure as well as mechanical and thermal characteristics of bilayer MoS₂. The in-plane elastic constants of seven twisted structures are determined by fitting the stress-strain relationship linearly. The results indicate all structures exhibit both mechanical stability and elastic isotropy, with exceptional rigidity compared to other two-dimensional materials. Based on calculated elastic constants, the thermal parameters, including sound velocities, Grüneisen parameter, and Debye temperature are obtained. Moreover, we investigate how tuning the twist angle affects thermal conductivity and observe a decreasing trend with an increase in the moiré lattice constant due to the increase of acoustic branches. Notably, at twist angle of 60°, we find a thermal conductivity value of 93.57 Wm⁻¹K⁻¹, whereas at an angle of 9.43°, it reaches 9.09 Wm⁻¹K⁻¹, representing an approximate reduction of 90 % in the thermal conductivity. These findings offer valuable insights into understanding how twisting influences the properties of bilayer MoS₂ and establish its potential as a promising material for thermoelectric devices.