Molecular dynamics of collisions between rough surfaces

This work describes the results of numerical simulations regarding the formation and evolution of local excitations at the surface of Ni crystals. Excitations were induced by carrying out a fracture process or a frictional collision between two rough surfaces. In the former case, excited atoms appear at the surfaces formed by fracture as a consequence of the sudden change in their coordination number. In the latter case, local excitations are instead connected with the stress fields originated from the contact between surface asperities. Surfaces are in both cases characterized by an inhomogeneous distribution of energy and temperature, which gives rise to a certain number of excited regions of different size. The properties of the different groups of excited atoms were monitored as a function of time to estimate their lifetime and excitation degree. The possible effect of local excitations on the kinetics of solid-gas reactions is also qualitatively inferred.