Interfacial Interactions and Tribological Behaviour of Metal-Oxide/2D-Material Contacts

This work combines experimental atomic force microscopy (AFM) and DFT simulations to study oxidized metal (oxidized copper & titanium) and 2D material (graphene & MoS2) interfaces. Combining AFM and DFT allowed identifying the interfacial interaction and established a correlation between tribological behavior, interfacial charge distribution, and variations in the potential energy profile with sliding along the metal/2D-materials interfaces. The TiO2 (rutile) and CuO (cupric oxide) metal oxides were mostly found to chemisorb along the interface with the 2D-materials. Both the metal-oxide counter-surfaces (TiO2 and CuO) exhibited higher friction force and adhesion on graphene than on MoS2. The CuO surface was inferred to be copper rich based on comparison with DFT simulations. The interfacial electronic charge distribution and relative energy change were identified to strongly influence sliding and adhesive behavior between oxidized-metal/2D-material contacts when considering only electronic effects in the DFT simulations. More homogenous interfacial charge distribution/sharing and lower surface energy variation, as found on the MoS2 surfaces, were identified to lower friction and adhesion. Non-electronic effects not captured by simulations were found to likely dominate interfacial shear strength measurements experimentally. Therefore, MoS2 should be used in interfacial applications involving TiO2 and copper rich CuO surfaces requiring lower adhesion and friction.