Graphene has demonstrated tremendous potentials as solid lubricants to reduce the friction force at the sliding interfaces. Its lubrication performance was found to be dependent on the mechanical properties of substrate. Here, we investigate the effect of substrate stiffness on the load-oriented thickness-dependent friction behavior of graphene sliding against a diamond tip using molecular dynamics simulations. It is found that the friction force increases about 6.4 times immediately when the load reaches a critical value to induce the formation of covalent bonds at the sliding interface. Below the critical load, single-layer graphene exhibits the smaller friction force than double-layer graphene when supported by high substrate stiffness. The friction reduction can be achieved by increasing the substrate stiffness or decreasing the sliding velocity. However, the critical load of rigid substrate-supported graphene (out-of-plane stiffness: 2167.5 N/m) is 37% lower than that of suspended graphene (out-of-plane stiffness: 115.1 N/m), which promotes the occurrence of tribo-chemical reactions during the sliding process. Such promotion is attributed to the enrichment of atomic charge at the sliding interface confirmed by density function theory calculations. This work offers a useful guidance to fabricate the high-performance nanodevices lubricated by nanomaterials with lamellar atomic structures for the tunable friction characteristics.
NSTL
Elsevier