Interaction between graphene layers and the mechanisms of graphite's superlubricity and self-retraction.

Graphene layer-layer interaction is explored as a function of the misorientation angle. A stepwise potential energy surface (PES), where the optimized commensurate configuration (AB stacking) corresponds to the global minimum and all incommensurate configurations correspond to nearly equal energies, is shown. The stepwise behavior is attributed to the alternating appearance of AB and AA stacking-like areas and the transition areas between them. Further, the PES of most incommensurate configurations is found to be ultra-smooth. Based on this, the puzzling experimental observation of graphite flake self-retraction is successfully explained.