Electronic structure of anodic oxide films formed on cobalt by cyclic voltammetry

The chemical composition and degrees of oxidation of thin oxides films formed on cobalt by cyclic voltammetry have been investigated by Auger electron spectroscopy and XPS analysis. In addition the electronic properties of the films have been examined by capacitance measurements using the Mott–Schottky method and photoelectrochemistry. The analytical results show that the thickness of the cobalt oxide films increases with the number of cycles and varies from a few tens to a few hundreds of angströms. When observed by transmission electron microscopy and diffraction, the films appear compact and well crystallised (spinel structure). Capacitance measurements show that both very thin and relatively thick films exhibit p-type semiconductivity. The band structure model proposed and the interpretation of the oxidation processes in terms of lattice ionic defects, can explain the film growth mechanism. The study shows how the electric fields created by the development of space charges influence both ionic transport and electronic transfer of charges.