Atomic Stick-Slip Friction Between Commensurate Self-Assembled Monolayers

Molecular dynamics (MD) simulations have been used to examine the friction between commensurate self-assembled monolayers (SAMs) on Au (111). The discrepancy between sawtoothed friction force and the discontinuous molecular movements reveals the complex dynamics of the closed-packing chains under shearing. Molecules in the lower monolayer can be divided into two groups with a phase difference of π. The periodic motion of the molecules is not synchronous with the frictional stick-slip loops, which result in a second-order valley in friction curves.