Influence of surface morphology on the oxidation of metal electrodes studied by in-situ grazing incidence x-ray diffractometry

The successful application of in-situ grazing incidence x-ray diffractometr y (GIXD) for the investigation of oxidation processes at copper electrodes in pH 12 electrolytes is demonstrated. A penetration/escape depth of about 1 mu m could be detected for a smooth polycrystalline copper foil and an x- ray incidence angle of 1.7 degrees Oxide layers generated at overpotentials less than about 0.5 V in respect to the equilibrium formation potentials o f Cu2O or CuO, respectively, showed a dependence of the crystalline oxide f ormation on the defect density of the copper substrate. Highly disordered g round or polished specimens exhibited an order of magnitude higher GIXD ref lexes from crystalline Cu2O than electrodeposited copper. Beyond overpotent ials of 0.5 V, this epitaxial information for the Cu2O crystal growth becam e irrelevant. Further, GLXD turned out to be an appropriate tool to monitor atmospheric corrosion processes under thin humidity films with oxygen acce ss. When oxygen diffusion through the polymer window membrane is allowed, o xygen reduction led to the concurrent formation of a crystalline CuO phase coexisting with amorphous Cu(OH)(2) and Cu2O, though the potential was kept in the region of Cu2O.