I. Preda, A. Gutiérrez, M. Abbate, F. Yubero, J. Méndez, L. Alvarez, L. Soriano
Physical Review B, 77 (2008) 075411 (1-7)
We report the Ni2p x-ray photoelectron spectra of NiO thin films grown on different oxide substrates, namely, SiO2, Al2O3, and MgO. The main line of the Ni2p spectra is attributed to the bulk component, and the shoulder at 1.5eV higher binding energies to the surface component. The spectra of the NiO thin films show strong differences with respect to that of bulk NiO. The energy separation between the main peak and the shoulder increases with the substrate covalence. This indicates the strong covalent interactions between the NiO thin films and the oxide substrates, and reflects changes in the bonding at the interface from a more ionic to a more covalent interaction. These conclusions are supported by cluster model calculations with a reduced O2p−Ni3d hybridization.