Morphology of the $Cu2O$ surface oxide phase formed on Cu(100) at high temperature

We have observed the nucleation and growth of the $Cu2O$ surface oxide on a Cu(100) surface at 870 K using low energy electron microscopy. Nucleating on a surface exhibiting the $(2×22)R45°-O$ overlayer, this phase caused the overall step morphology to change from long, mostly straight narrow-terraced step bunches to broad, deeply curved terraces with more highly bunched steps. Using x-ray photoelectron spectroscopy, we have measured an upper bound of 2.6 ML (monolayer) for the surface oxygen coverage at which we observed this oxide phase. The lattice constant of the observed oxide phase matches that of the (111) face of $Cu2O$⁠. We postulate that the oxide does not form epitaxially on this surface at this temperature due to interactions with the centered rectangular phase of oxygen, which provides a nearly hexagonal template for the $Cu2O(111)$ hexagonal structure.