Valence band study of LaNiO3−δ thin films

The resonant photoemission spectroscopy was used to study the surface electronic structure under La 4d→4f and Ni 3p→3d photo-excitation of thin LaNiO3−δ films after annealing in ultrahigh vacuum above dehydration temperature.The giant resonance in La 5p and La 5s peaks intensity observed at excitation energy corresponding to a La 4d→4f threshold is accompanied by resonance of the N4,5O2,3O2,3 and N4,5O2,3V Auger peaks. The enhancement in the intensity of valence band maxima (at about 6 eV) may be explained by the small mixing of the La 5d ionic character to the O 2p valence band. The week resonant features observed in the valence band spectra under Ni 3p→3d threshold indicate the loss of nickel species at the LaNiO3−δ film surface after heat treatment.