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

XPS and factor analysis (FA) have been applied to characterize the sur face state of three polycrystalline cobalt oxide samples with differen t crystallographic bulk structure (CO3O4 and CoO) and surface characte ristics. The study of the thermal behaviour of the O1s and Co2p spectr a 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 sha pe 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 compone nt 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 heate d;at that temperature, components Co-III and Co-I were generated. Co-I disappears, while the intensity of components O-II and Co-III increas es when the samples are exposed to O-2. The most intense O-I species i s attributed to oxygen atoms in sites with a well defined coordination . Species O-II and O-III are attributed to low coordinated oxygen atom s at special sites or domains of the surface where the covalence of th e Co-O bond is higher. Differences in the relative abundance of the th ree oxygen components, either during outgassing or after Ar+ sputterin g, are dependent on the texture of the three samples expressed in term s of their respective surface areas.