An Electron Spectroscopic Study of the Cobalt(101̄2)-Oxygen Interaction: Chemisorption Properties, Oxide Growth and Oxidation States of the Surface Metal Ions

Abstract

The interaction of oxygen with the stepped (101̄2) surface of cobalt has been investigated over a range of temperature (300–800 K) and pressure (10⁻⁷−10⁺¹ Torr) by XPS, UPS and LEED. After completion of a layer of chemisorbed atoms, oxygen uptake proceeds by the nucleation and growth of CoO. An examination of the satellite intensities associated with the Co(2p) levels yields no evidence for the formation of the higher oxide, and valence band UP spectra point to the same conclusion. However, the LEED results indicate that poorly ordered domains of the (100) plane of the Co₃O₄ spinel lattice are formed after extensive oxidation. A model is proposed which accounts for these observations; it also provides a basis for reconciling a number of conflicting reports in the literature.