Deformation-coupled dual-scale stick-slip friction in covalently bonded moiré superstructures

While twist angle and stacking order have long been established as degrees of freedom for manipulating moiré superlattices and elasticity in two-dimensional (2D) material contacts, interlayer covalent bonding offers a distinct and efficient pathway to engineer these properties with enhanced structural tunability. Despite this potential, how such covalent modifications govern tribological behavior remains largely unexplored. Here, we employ molecular dynamics simulations to investigate the friction characteristics of interlayer-bonded strained bilayer graphene (IB-SBG) featuring tunable herringbone and honeycomb wrinkle morphologies. Our results reveal dual-scale stick-slip friction comprising long-range modulation at the moiré periodicity superimposed on atomic-scale stick-slip events. Wrinkle morphology governs the friction response: along the armchair sliding direction, herringbone wrinkles exhibit single stick-slip cycles per period, whereas honeycomb wrinkles display double cycles reflecting their closed-cell topologies, with both configurations showing direction-dependent friction signatures. Force decomposition analysis reveals that friction predominantly arises from in-plane deformation of the wrinkle, with interlayer covalent bonds acting as geometric anchors that localize strain and convert it into lateral resistance. A modified deformation-coupled Prandtl-Tomlinson (MDC-PT) model is developed that successfully captures these dual-scale characteristics for both configurations, establishing a unified theoretical framework for friction in covalently constrained moiré systems. Furthermore, honeycomb wrinkles exhibit negative differential friction at low normal loads, a phenomenon inaccessible to open-ridge herringbone morphologies. These findings provide both a generalizable theoretical framework and design principles for engineering programmable nanotribological interfaces through moiré morphology control. (Figure presented.)