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 O2 have permitted verification of the existence of three components at the O1s spectra with binding energies at 529.6 (OI), 531.1 (OII) and 532.1 eV (OIII) and three components at the Co2p level. The shape of these components is similar to the Co2p spectra of Co3O4 (CoIII), CoO (CoII) and Co0 (CoI) compounds. In the three samples component OII yields component OIII by heating at 473 K < T < 673 K. Then, the intensity of species OIII and OI decreases to a minimum at 923 K. Simultaneously, component CoIII, the most abundant in the original samples, yields component CoII by outgassing at T > 473 K. CoII is the only one detected at 923 K. After Ar+ sputtering of the samples heated at that temperature, components CoIII and CoI were generated. CoI disappears, while the intensity of components OII and CoIII increases when the samples are exposed to O2. The most intense OI species is attributed to oxygen atoms in sites with a well defined coordination. Species OII and OIII 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.