▎ 摘　　要

The tribological properties of graphene have attracted intensive attentions over the past few years. It was found that the frictional behavior of multilayer graphene was dependent on the multilayer thickness. However, the origin for such phenomenon is still under discussion. In this study, the mechanism of the thickness-dependent friction was explored based on molecular dynamics simulations of the scratching process of multilayer graphene. We found that the friction coefficient dropped dramatically as the number of layers increased under the same scratch depth. Further analysis of the graphene structure variation during the scratching process showed that the amount of the cross-linking decreased when the number of layers increased, which accounts for the dependence of the friction coefficient on the thickness. Finally, a novel mechanism was proposed that the thickness-dependent friction of multilayer graphene was caused by the formation of cross-linking between graphene layers. This study provides basic understanding of the origin of friction in multilayer graphene.