Comparison of aqueous and native oxide formation on Cu(111)

We present the results of an x-ray diffraction investigation of the formati on of oxide on electropolished Cu(111) surfaces, both in situ at pH 4.5 and in air. In both cases the oxide is found to be crystalline cuprite and epi taxially aligned with the substrate, but with two possible epitaxial orient ations. We followed the progress of oxidation by monitoring the shapes of t he diffraction peaks for the two orientations as a function of time and pot ential. There is a narrow potential region where the oxide is a single mono layer thick. Beyond that, only one of the two oxide orientations becomes th icker, and does so in an inhomogeneous manner, thickening in narrow regions before it spreads. (C) 1999 American Institute of Physics. [S0021-9606(99) 70710-5].