Resolving atomic-scale stick-slip and sub-moiré frictional modulation in twisted bilayers with variable tip sizes

The nanoscale frictional properties of moiré superlattices in twisted MoS₂bilayers are governed by tip-sample interactions and the tunable moiré potential, modulated by twist angle (0°-6°) and strain, enabling tailored frictional responses. However, discrepancies between sharp-tip and larger-tip friction force microscopy measurements obscure lattice-scale dynamics, with theoretical models offering limited insight into tip-size and interlayer displacement effects on frictional amplitude. This study employs molecular dynamics simulations to probe the frictional behaviour of MoS₂bilayers across tip sizes (0.5-3 nm), revealing a transition from multiscale behaviour-lattice-scale stick-slip (0.32 nm) with sub-moiré amplitude modulation (0.15-1.2 nN)-to moiré-dominated periodicity (5-32 nm) as tip size increases. Larger tips average atomic-scale oscillations, shifting amplitude maxima from AB to AA stacking, a phenomenon driven by enhanced interlayer displacement. These findings resolve experimental inconsistencies, demonstrating lattice-scale periodicity's presence and its sub-moiré variation for the first time. This work provides insights into nanoscale tribological mechanisms in 2D materials, advocating high-resolution probes (<2 nm) for accurate frictional mapping and informing the design of moiré-based systems with engineered frictional properties.