Final states after Ni2 p photoemission in the nickel—oxygen system

Abstract

The Ni2 p, Ni3 p, Li1 s and O1 s XPS spectra were measured for single crystal NiO and Li x Ni 1− x O, cleaved and scraped, respectively, in a spectrometer. The cleaved surface had Ni2 p 3 2 peaks at 853.9 and 855.8 eV with an intensity ratio of 1:1, where the FWHM of the former was smaller than that of the latter. The intensity ratio decreased with doping of lithium. Although these peaks had previously been ascribed to di- and tri-valent nickel ions in their ground states, we interpret them here as follows. The peaks at 854 and 856 eV correspond to the final states of Ni2 p 3 d 9 L and Ni2 p 3 d 10 L 2, where the underline denotes an electron hole. An O2 p electron hole in the ground state is necessary to give the latter final state. The doping of lithium increases the density of electron holes and the intensity of the latter final state. The spectral profile of Ni3 p did not change with the addition of lithium. The binding energies of Li1 s from the particle surface and the bulk were 55.5 and 53.5 eV, respectively. The large shift is associated with surface contamination. The O1 s spectrum of the cleaved NiO had two peaks at 529.5 and 531.5 eV with an intensity ratio of 1:0.1. The FWHM of the peaks at 529.5 eV for NiO and Li 0.3Ni 0.70 were 1.0 and 1.7 eV, respectively. The binding energy of the main peak for LiNiO 2 was 528.7 eV.