Enhanced Mass Transfer in the Step Edge Induced Oxidation on Cu(100) Surface

In situ TEM experiments have shown that the oxidation of stepped Cu(100) surface results in a flat Cu₂O film, which is different from the 3D oxide island structure that usually forms on a flat Cu surface. The mass transport process originating from Cu adatoms that detach from the step edge is argued to be responsible for the different oxide growth behavior. Using molecular dynamics in conjunction with a reactive force field (ReaxFF), we show that the mass transport from the step edge to the flat terrace is enhanced by the unevenly distributed oxygen adatoms on the step top compared to the flat terrace. The ReaxFF force field is optimized using density functional theory calculated energetics and kinetic barriers on various Cu surface models. We investigate two possible mechanisms that can trigger Cu transport: (1) strain due to lattice mismatch between Cu and Cu₂O and (2) electrostatic interactions. We show that the formation and diffusion of Cu–O clusters can accelerate the Cu transport process, especially in the presence of surface vacancy defects. Our atomistic simulations demonstrate that the Cu atom detachment progresses from the top of the step edge into deeper layers, and the detachment rate is enhanced with elevated temperatures.