Mechanism of ultra-low friction of multilayer graphene studied by all atom molecular dynamics
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A molecular dynamics simulation is used to investigate the occurrence of thermal escape motion of a graphene transfer layer in all atom levels. In the simulation, the substrate is modelled as a 3-layer graphene slab, and the transfer layer as layered circle graphene sheets. The top graphene sheet is force to move in a constant velocity. After the sliding motion, the dynamics of the transfer layers showed different dependences on the sliding velocity and the size of the graphene sheet. Only when the sliding motion is low enough and the size is large enough, is the thermal escape motion found. When the sliding speed is too high, the lower layers cannot follow the top sheet. When the graphene sheet is too small, the lower layered structure is broken due to an internal motion. The latter motion is not found during the study using the previous coarse-grained simulation. The size of the layers experimentally observed is the same as this simulation, and when the sliding motion is low enough, a low friction is observed. Thus, a low friction is indicated as a result of the thermal escape motion.