Comparison of Frictional Properties of CVD-Grown MoS(2) and Graphene Films under Dry Sliding Conditions

In the present study, dry friction and wear properties of atomically thin CVD-grown graphene and MoS(2) films on SiO(2)/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 MoS(2) films, which were directly grown on the SiO(2)/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 SiO(2)/Si substrate due to its wet transfer from a Cu foil to the substrate. The MoS(2) 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 SiO(2)/Si were the main causes of the superiority of the MoS(2) film compared to the graphene film. Mild wear occurred in a layer-by-layer fashion at low contact pressure for the MoS(2) film. At high contact pressure, severe wear occurred due to failure at the boundary between the MoS(2) films and the underlying substrates. At both contact pressures, friction did not increase immediately after the removal of the MoS(2) film from the SiO(2)/Si substrate because the film transferred onto the counter sliding surface and served as a lubricant.