The role of speed in atomic scale wear

Decoupling the role of various stress components during atomic scale wear such as normal, shear, and hoop stressesremains one of the biggest challenges preventing a full understanding of how wear proceeds. Here we model atomic scale wear as two sets of thermally activated processes, where normal load drives bonding between surfaces, and lateral motion biases surface site hopping in the direction of sliding. We further utilize the model to explain the velocity-dependent wear behavior at the interface between an atomic force microscope tip and graphene oxide. The experimental and theoretical results show that, at tip speeds slow enough to saturate bond formation at the tipsample interface, breaking these bonds is a thermally activated process with a rate that increases with speed. In addition, the theoretical model predicts additional wear dependencies on velocity also observed in the literature, where a decrease in wear with increasing velocity occurs when the tip moves too quickly for bonds to form on the surface, and wear independent of velocity occurs at high loads when the thermodynamic barrier to wear is vanishingly small. This theoretical framework potentially unifies the range of velocity-dependent wear behaviors found in previous studies of atomic scale wear.