Energetics of oxygen-induced faceting on Cu(115)

We have used surface x-ray diffraction to observe the oxygen-induced faceting of the Cu(115) surface in real time. We find that the surface morphological evolution is driven by the formation of O/Cu(104) facets: O exposure induces spinodal decomposition of the (115) surface into (104) and (014) facets, which form spontaneously, and also stepped facets, whose orientation gradually changes from (115) to (113) as the (104) facets grow. We identify three temperature regimes that have qualitatively different faceting processes, allowing us to determine the temperature-dependent equilibrium crystal shape for part of the O/Cu system. Semiquantitative explanations are given in terms of the Wulff construction. During the faceting process, the time evolution follows a slow dynamic scaling, consistent with either a logarithmic or power-law behavior, driven by the rate of incorporation of O onto the surface.