Molecular dynamics characterization of the contact between clean metallic surfaces with nanoscale asperities

Abstract

We use molecular dynamics (MD) simulations to characterize the tensile strength of contacts formed between various clean platinum surfaces with nanoscale asperities. Both commensurate contacts between (001) and (111) surfaces and incommensurate (001) ones are considered over a wide range of asperity sizes. In cyclic closing and opening, fresh asperities that form contacts for the first time show significant plastic deformation; this leads to a reduction in the effective contact area during the first few cycles, after which steady state is achieved both in terms of contact size and the pull-out force necessary to open the contacts. As is the case for commensurate surfaces [H. Kim and A. Strachan, Phys. Rev. Lett. 104, 215504 (2010)], the strength of the metallic bridges that form in incommensurate contacts exhibit strong size effects; their strength increases with decreasing size until a length of \ensuremath{\sim}5 nm, below which weakening is observed. Commensurate contacts lead to stronger bridges than incommensurate ones but only during the initial closing events; after steady state is achieved, commensurate and incommensurate (001) surfaces lead to bridges of similar strengths.