Structural and Chemical Properties of NiO<sub>x</sub> Thin Films: Oxygen Vacancy Formation in O<sub>2</sub> Atmosphere
Raoul Blume, Wolfram Calvet, A. Ghafari, Thomas Mayer, Axel Knop‐Gericke, Robert Schlögl
Abstract
Abstract NiO x films on Si(111) were put in contact with oxygen at elevated temperatures. During heating and cooling in oxygen atmosphere Near Ambient Pressure (NAP)‐XPS and ‐XAS and work function (WF) measurements reveal the creation and replenishing of oxygen vacancies in dependence of temperature. Oxygen vacancies manifest themselves as a distinct O1s feature at 528.9 eV on the low binding energy side of the main NiO peak as well as by a distinct deviation of the Ni2p 3/2 spectral features from the typical NiO spectra. DFT calculations reveal that the presence of oxygen vacancies leads to a charge redistribution and altered bond lengths of the atoms surrounding the vacancies causing the observed spectral changes. Furthermore, we observed that a broadening of the lowest energy peak in the O K‐edge spectra can be attributed to oxygen vacancies. In the presence of oxygen vacancies, the WF is lowered by 0.1 eV.