THE STATE OF THE OXYGEN AT THE SURFACE OF POLYCRYSTALLINE COBALT OXIDE

XPS and factor analysis (FA) have been applied to characterize the surface state of three polycrystalline cobalt oxide samples with different crystallographic bulk structure (CO3O4 and CoO) and surface characteristics. The study of the thermal behaviour of the O1s and Co2p spectra and of their changes as an effect of Ar+ bombardment and exposure to O-2 have permitted verification of the existence of three components at: the O Is spectra with binding energies at 529.6 (O-I), 531.1 (O-II) and 532.1 eV (O-III) and three components at the Co2p level. The shape of these components is similar to the Co2p spectra of Co3O4 (Co-III), CoO (Co-II) and Co-0 (Co-I) compounds. In the three samples component O-II yields component O-III by heating at 473 K < T < 673 K. Then, the intensity of species O-III and O-I decreases to a minimum at 923 K. Simultaneously, component Co-III, the most abundant in the original samples, yields component Co-II by outgassing at T > 473 K. Con is the only one detected at 923 K. After Ar+ sputtering of the samples heated;at that temperature, components Co-III and Co-I were generated. Co-I disappears, while the intensity of components O-II and Co-III increases when the samples are exposed to O-2. The most intense O-I species is attributed to oxygen atoms in sites with a well defined coordination. Species O-II and O-III are attributed to low coordinated oxygen atoms at special sites or domains of the surface where the covalence of the Co-O bond is higher. Differences in the relative abundance of the three oxygen components, either during outgassing or after Ar+ sputtering, are dependent on the texture of the three samples expressed in terms of their respective surface areas.