In the present study, dry friction and wear properties of atomically thin CVD-grown graphene and MoS₂ films on SiO₂/Si substrates were compared at low (72 MPa) and high (378 MPa) contact pressures. Analysis of atomic force microscopy images of these films verified that the MoS₂ films, which were directly grown on the SiO₂/Si substrates, had clean surfaces and made conformal contacts with the substrates. In contrast, the graphene film showed many contaminants on its surface and was loosely bonded with its SiO₂/Si substrate due to its wet transfer from a Cu foil to the substrate. The MoS₂ film exhibited friction and wear properties superior to those of the graphene film both at low and high contact pressures. We found that the clean sliding surface and strong bonding with SiO₂/Si were the main causes of the superiority of the MoS₂ film compared to the graphene film. Mild wear occurred in a layer-by-layer fashion at low contact pressure for the MoS₂ film. At high contact pressure, severe wear occurred due to failure at the boundary between the MoS₂ films and the underlying substrates. At both contact pressures, friction did not increase immediately after the removal of the MoS₂ film from the SiO₂/Si substrate because the film transferred onto the counter sliding surface and served as a lubricant.
Keywords: Chemical Vapor Deposition; MoS2; friction; graphene; wear.