Photoemission Study of the Interaction of Oxygen with Co Surface of Metastable bcc Phase

Metastable, weakly ordered ultrathin Co films with he phase were grown on GaAs （100）surface, and the coverage dependence of oxygen adsorption on the sulface of Co films was studied at room temperature by synchrotron radiation photoemission and XPS, For the exposuire between 1~4L of O₂, oxygen adsorbs dissociatively, Hider exposure corresponds to nucleation and formation of surface CoO phase from the analysis of valence-band spectra and Co3p emission. Higher temperature exceeding 470K causes the dissolution of oxygen into the Co matrix, The decomposition of O1s XPS indicates the existence of two species of oxygen corresponding to the different adsorbed sites.