Density functional study of oxygen on Cu(100) and Cu(110) surfaces

Using density-functional theory within the generalized gradient approximation, we investigate the interaction between atomic oxygen and Cu(100) and Cu(110) surfaces. We consider the adsorption of oxygen at various on-surface and subsurface sites of Cu(100) for coverages of 1/8 to 1 monolayers (ML). We find that oxygen at a coverage of 1/2 ML preferably binds to Cu(100) in a missing-row surface reconstruction, while oxygen adsorption on the nonreconstructed surface is preferred at 1/4 ML coverage consistent with experimental results. For Cu(110), we consider oxygen binding to both nonreconstructed and added-row reconstructions at various coverages. For coverages up to 1/2 ML coverage, the most stable configuration is predicted to be a p(2 x 1) missing-row structure. At higher oxygen exposures, a surface transition to a c(6 x 2) added strand configuration with 2/3 ML oxygen coverage occurs. Through surface Gibbs free energies, taking into account temperature and oxygen partial pressure, we construct (p, T) surface phase diagrams for O/Cu(100) and O/Cu(110). On both crystal faces, oxygenated surface structures are stable prior to bulk oxidation. We combine our results with equivalent (p, T) surface free energy data for the O/Cu(111) surface to predict the morphology of copper nanoparticles in an oxygen environment.