Valence band study of LaNiO3−δ thin films

Abstract

a b s t r a c tThe resonant photoemission spectroscopy was used to study the surface electronic structure under La 4d-4f and Ni 3p-3d photo-excitation of thin LaNiO 3 À d 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 4,5 O 2,3 O 2,3 and N 4,5 O 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 3 À d film surface after heat treatment.