XPS/UPS study of the oxidation of La and LaNi5 and of the electronic structure of LaNi5

The VB and the core levels of clean and oxygen exposed bulk samples of La and LaNi5 were investigated by means of photoelectron spectroscopy using MgKα (XPS) and HeII (UPS) radiation. The HeII VB of La only shows 1.3 eV FWHM. The VB of LaNi5 is mainly derived from the VB of Ni. The low binding energy satellite of the La3d core level (4f1 final state) is much stronger in LaNi5 than in La, reflecting the better screening of the 3d core-hole by filling of f states. The spectra indicate clearly that La oxidizes and not Ni upon the exposure of LaNi5 to small amounts of oxygen.