Stick-Slip Dynamics of Moir ' e Superstructures in Polycrystalline 2D Material Interfaces
X Gao and M Urbakh and O Hod, PHYSICAL REVIEW LETTERS, 129, 276101 (2022).
A new frictional mechanism, based on collective stick-slip motion of moire superstructures acrosspolycrystalline two-dimensional material interfaces, is predicted. The dissipative stick-slip behaviororiginates from an energetic bistability between low- and high-commensurability configurations of large-scale moire superstructures. When the grain boundary separates between grains of small and largeinterfacial twist angle, the corresponding moire periods are significantly different, resulting in forbiddengrain boundary crossing of the moire superstructures during shear induced motion. For small twist anglegrains, where the moire periods are much larger than the lattice constant, this results in multiple reflectionsof collective surface waves between the surrounding grain boundaries. In combination with the individualgrain boundary dislocation snap-through buckling mechanism dominating at the low normal load regime,the friction exhibits nonmonotonic behavior with the normal load. While the discovered phenomenon isdemonstrated for h-BN/graphene polycrystalline junctions, it is expected to be of general nature and occurin many other large- scale layered material interfaces.
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