Nonmonotonic Enhancement of Friction Regulation via Strain-Induced Moiré Patterns on MoS Substrate Surface.

Traditionally, strain-induced moiré patterns at the friction interface can produce superlubrication. Here, we construct moiré patterns on the surface of a two-layer MoS substrate through applying biaxial strain to the bottom layer of the substrate and investigate the effect of moiré patterns on friction energy dissipation. Results indicate friction enhances nonmonotonically with an increase of strain. Notably, two types of frictional dissipation channels have been discovered, corresponding to washboard and moiré-washboard frequencies. Based on this discovery, we determine that the nonmonotonic increase in friction is the result of coupling enhancement of the two dissipative channels and nonmonotonic change in moiré surface roughness. Moreover, friction gradually evolves into a monotonic increase with strain as the adhesion factor between substrate layers enhances. This is because strong interlayer interaction leads to an extremely low moiré barrier, which in turn makes moiré-surface roughness vary minimally, and thus the coupling of two dissipative channels plays a dominant role in friction. Our observations provide strategies for actively controlling friction in 2D material systems.