Surface stability of epitaxial LaNiO3-δthin films

Thin LaNiO 3-δ films with pseudocubic (100) preferred orientation were prepared by reactive DC magnetron sputtering and in situ annealed in O2 and vacuum.X-ray photoelectron spectroscopy (XPS) was used to determine the variation in composition of the films under high temperature annealing.The experimental O 1s and La 3d -Ni 2p 3/2 spectra of LaNiO 3-δ films was analysed in terms of O 2-, O -/(OH) -, and weakly adsorbed oxygen species.It was shown that the change in the type of conductivity from metallic to semiconducting one is accompanied by a marked increase in the intensity of the lateral (∼531 eV) peak of oxygen.The quantitative analyses of La 3d -Ni 2p 3/2 spectra show that the Ni/La concentration ratio significantly decreases after heating above the dehydration temperature.These variations in conductivity and surface composition were attributed to the loss of lattice oxygen with subsequent adsorption of O -and (OH) -anions and weakly adsorbed oxygen species from ambient air.