Study of surface oxidation of rare-earth metals by photoelectron spectroscopy

Abstract

Surface oxidation of La, Ce, Sm and Tb metals has been investigated by He(II) ultraviolet photoelectron spectroscopy (u.p.s.) and X-ray photoelectron spectroscopy (X.p.s.). Oxidation of La gives rise to La₂O₃ on the surface. While Ce₂O₃ appears to be the stable oxide on the surface, we find evidence for formation of CeO₂ at high oxygen exposure. Valence band of Sm clearly shows the presence of both divalent and trivalent states due to interconfigurational fluctuation. Exposure of Sm to oxygen first depletes the divalent Sm at the surface. While Sm₂O₃ is the stable oxide on the surface of Sm, Tb₂O₃ is the stable oxide on the surface of Tb (and not any of the higher oxides).