Surface effects in the Ni 2p x-ray photoemission spectra of NiO

We report experimental and theoretical evidence of surface effects in the Ni 2p x-ray photoemission spectra (XPS) of NiO. The Ni 2p(3/2) surface-enhanced XPS of a NiO sample show a relative enhancement of the intensity of the known satellite at 1.5 eV higher binding energy from the main line, indicating a considerable surface contribution of this satellite. The results are discussed in terms of bulk-octahedral and surface-pyramidal Ni symmetries. Other contributions, like nonlocal screening effects, cannot be neglected.