▎ 摘　　要

Nanofriction with few layers of graphene as lubrication is an interesting issue recently, and it provides a quite important guide for modeling the nanofriction properties of nanodevice. Based on the molecular dynamics (MD) simulations, nanofriction properties of a silicon tip sliding on different graphene layers with or without substrate were studied systemically. We revealed that the friction of these systems exhibits clearly the even-odd oscillations with different thickness of graphene, and we further demonstrated that such even-odd oscillations behavior is totally independent of the size of the silicon tips, as well as applying normal loadings. The underlying physics of this intriguing phenomenon is attributed to the oscillations of indirect-contact-atom-number between top and sublayers of suspended graphene. Furthermore, we showed that such indirect contact oscillations would be reflected by the direct contact oscillations between the tip and the top-layer graphene when graphene lubrication layers on a rigid substrate. Overall, our new findings not only enrich the nanofriction mechanism of graphene lubrication systems, but also introduce a new way to design the nanofriction systems with two-dimensional (2D) van der Waals materials as lubrications. (c) 2019 Author(s).