The influence of defects on the Ni 2p and O 1s XPS of NiO

The Ni 2p and O 1s XPS of NiO single crystals were measured using monochromatic Al K alpha radiation. Different treatments of the crystals allow the authors to give a description of the influence of defects on these spectra. The Ni 2p3/2 spectrum of in-situ-cleaved NiO exhibits clearly visible features at 854.1 ev 855.6 eV and 861 eV. The intensity ratio changes after ion bombardment and an additional peak at 852.2 eV appears. Apart from a slight increase in linewidth the O 1s spectrum remains unchanged. The O 1s spectrum from an in-situ-cleaved NiO single crystal exhibits only a single peak at 529.4 eV which can be fitted by a Gaussian line profile. Further measurements allow the authors to attribute the well known O 1s satellite at 531.2 eV to emission from oxygen-containing species adsorbed at defects.