Interlayer friction and superlubricity in bilayer graphene and MoS2/MoSe2 van der Waals heterostructures

Due to the weak van der Waals interaction between two-dimensional materials, one can stack or twist two-dimensional materials to obtain novel or enhanced physical and chemical properties. In this study, the relationship between twist angle and friction properties of bilayer graphene and MoS2/MoSe2 van der Waals hetemstructures was studied using molecular dynamics simulations by considering the effects of temperature, relative velocity, slip direction and normal force. The results show that for twisted bilayer graphene, the friction force reduced significantly in incommensurate stacking, and the superlubricity (mu <= 0.001) happens. For MoS2/MoSe2 heterostructures, the superlubricity is achieved in the range of twist angles of 9 degrees <= theta <= 51 degrees. In both systems, the friction force increases with the increase of temperature, and increases linearly with increasing of normal force and relative velocity. And in the range of the twist angle close to aligned commensurate contact (theta <= 10 and theta >= 50 degrees), the friction force changes more significantly. After a certain angle of rotation (under misaligned incommensurate state), the anisotropy of friction degenerated remarkably, which is two orders of magnitude lower than that of commensurate stacking. These results deepen the understanding of superlubricity in two-dimensional materials, and will also shed light on the applications of two-dimensional materials.