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

This work combines experimental atomic force microscopy (AFM) and density functional theory (DFT) simulations to study oxidized-metal (oxidized copper & titanium) and 2D-material (graphene & MoS 2 ) 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 TiO 2 (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 (TiO 2 and CuO) exhibited higher friction force and adhesion on graphene than on MoS 2 . 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 MoS 2 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, MoS 2 should be used in interfacial applications involving TiO 2 and copper-rich CuO surfaces requiring lower adhesion and friction. Graphical abstract