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

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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 $p(2\ifmmode\times\else\texttimes\fi{}1)$ missing-row structure. At higher oxygen exposures, a surface transition to a $c(6\ifmmode\times\else\texttimes\fi{}2)$ 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.