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

S Das and N Mohapatra and H Kumar, JOURNAL OF PHYSICS-CONDENSED MATTER, 37, 275001 (2025).

DOI: 10.1088/1361-648X/ade756

The nanoscale frictional properties of moir & eacute; superlattices in twisted MoS2 bilayers are governed by tip-sample interactions and the tunable moir & eacute; potential, modulated by twist angle (0 degrees-6 degrees) 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 MoS2 bilayers across tip sizes (0.5-3 nm), revealing a transition from multiscale behaviour- lattice-scale stick-slip (0.32 nm) with sub-moir & eacute; amplitude modulation (0.15-1.2 nN)-to moir & eacute;-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-moir & eacute; 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 moir & eacute;-based systems with engineered frictional properties.

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