Roughness picture of friction in dry nanoscale contacts

Large-scale molecular-dynamics simulations are performed to study friction in nanoscale single asperity contacts. The modeling system consists of a tip made of H-terminated diamond-like carbon and an H-terminated diamond sample. Simulations are carried out using a reactive bond-order interatomic potential integrated with dispersive interactions. A quantitative agreement in contact pressures and shear strengths is achieved between our simulations and previously reported experimental studies. We show that the roughness theories capture the correct physics of deformation at the nanoscale. Our study provides a consistent explanation of the widely observed transition from a linear to sublinear dependence of the friction force on the applied load and we demonstrate that both regimes of friction are governed by the same physical phenomenon. Specifically, we show that friction is controlled by the mean number of atoms that interact chemically across the contact interface.