Controlled friction on graphene via substrate deformation induced atomic pinning effect

Graphene's friction heavily depends on the substrate deformation; nevertheless, the mechanism behind such dependence has not been clarified. In this study, we reveal that the substrate deformation-induced pinning effect on the sliding tip, instead of the graphene's wrinkle height, determines the friction of graphene on top of it. With molecular dynamics simulations, we revealed that the surface deformation on the substrate underneath the graphene was inevitable, regardless of the substrate's hardness or lattice structure. Besides, such deformation, exhibiting as a dimple formed on the substrate's surface, is elastic and would fully recover upon unloading after the tip slides over. However, within the scope of the dimple, we observed a pinning effect occurring on the tip. By analyzing the spatial distribution of graphene atoms that interacted with the tip atom that endured the maximum resistant force, we proposed a quantitative evaluation on the extent of the deformation of the graphene and found that the deviation of the deformed graphene from its pristine status, which is significantly affected by the substrate deformation, exhibited a positive correlation with the pinning force on the tip, and thus the friction. The findings reported in the present study deepens our understanding of the origin of graphene's friction behaviors and provides an approach to control graphene's friction behaviors at the nanoscale.