Use of Factor Analysis and XPS To Study Defective Nickel Oxide

Article abstract of DOI:10.1021/j100186a056

The mathematical method of factor analysis has been used to analyze the Ni 2p_3/2 and O 1s photoelectron spectra of a nonstoichiometric nickel oxide sample with a high concentration of Ni³⁺ defects.The spectra of these two levels are characterized by main peaks (at 854.6 and 529.6 eV for the Ni 2p_3/2 and O 1s levels) and satellites at ca. 2 eV higher binding energy, whose intensity depends on the degree of nonstoichiometry.Heating in vacuum at T > 723 K produces a decrease in the intensity of these two satellites and the appearance of a new peak in the Ni 2p spectra at 852.6 eV due to Ni⁰.Factor analysis shows that these two phenomena are coupled.The existence of a new form of oxygen at 531.0 eV, unstable at 373 K under vacuum of after reaction with CO at 298 K, is also shown by this method.This new form, tentatively attributed to a peroxo-like species, is also generated after the adsorption of oxygen on the nickel oxide sample deeply reduced by Ar⁺ bombarding, a fact that points to its stabilization on surface unsaturated nickel sites, produced in high concentration by sputtering.