Valence band study of LaNiO sub(3- delta ) 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 LaNiO sub(3- delta ) 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 N sub(4,5)O sub(2,3)O sub(2,3) and N sub(4,5)O sub(2,3)V 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 LaNiO sub(3- delta ) film surface after heat treatment.