Step-Induced Oxygen Upward Diffusion on Stepped Cu(100) Surface

Surface defects such as step edges play an important role in determining the surface properties, affecting immensely the growth mechanisms and morphologies of the nanostructures in epitaxial film growth processes. Here, we probe the dynamics of the oxidation on stepped Cu(100) using molecular dynamic simulations in conjunction with a reactive force field, and we elucidate the mechanisms and energy barriers affecting the oxidation process. Molecular dynamic simulations show that the adsorbed oxygen adatoms are unevenly distributed on the stepped surface, favoring the top terrace. We show that this behavior is due to EhrlichSchwobel (ES) barrier effect. However, differently from the reduced interlayer self-diffusion in descending a step as in a conventional ES barrier effect, we find instead that the ES barrier reduces the ascending diffusion barrier for oxygen, promoting its transport across the step edge and enhancing oxidation of the upper terrace. Additionally, we find that the ES barrier is step-height dependent, where higher step edges reduce more the oxygen-ascending diffusion barrier and favor more oxidation of the upper terraces of stepped surfaces.