Role of chemical vs. physical interfacial interaction and adsorbed water on the tribology of ultrathin 2D-material/steel interfaces

Lubrication of steel using two-dimensional (2D)-materials has been a growing interest in recent years at the macro/microscale for wide range applications including lubricating 440 C-steel satellite and automotive components. This work takes new approach comparing tribological behavior ultrathin-graphite ultrathin-MoS2 varying humidity against custom-fabricated counter-surface friction force microscopy. The presence oxides on is found to form stronger chemical interactions with MoS2, leading higher friction, interfacial-shear-strength adhesion as compared physically interacting steel/ultrathin-graphite interface. While water increases interface, an opposite trend observed steel/MoS2 where act temporary protective film suppress interaction.