Dual-Scale Friction Dynamics Associated with Moiré Superlattices in Layered Materials

The ultralow friction properties of 2D materials present significant potential for energy-saving application. Atomic force microscopy experiments on the moiré superlattice of stacked 2D materials reveal that, beyond atomic stick-slip dynamics, friction behaviors at the moiré scale introduce a new dominant energy dissipation mechanism. However, understanding these behaviors remains challenging due to the complex interplay between atomic and moiré scale effects. Here, through large-scale molecular dynamics simulations of a tip scanning on a graphene/h-BN heterostructure, it is demonstrated that transitions between stick-slip and smooth sliding behaviors can be tuned at both atomic and moiré scales. Specifically, atomic-scale friction behavior is governed by the commensurability of tip-surface contact, while moiré-scale friction behavior arises from a load-dependent competition between expulsive interactions at tip/surface-indentation region and adhesive interactions at tip/surface-ripple region. The moiré stick-slip behavior occurs due to the more rapid shift of the protruding domain wall region as the tip crossing it under higher load. Furthermore, greater stretching of graphene bonds during domain wall crossing enhances energy dissipation. This moiré stick-slip behavior persists, albeit attenuated, in tri-layer systems. This findings provide new insights into friction at multiple length scales and may inform future studies of friction in multilayer superlattices.