The identification and characterisation of mixed oxidation states at oxidised titanium surfaces by analysis of X-ray photoelectron spectra

Abstract

The interaction of oxygen with titanium has been studied by X-ray photoelectron spectroscopy. Methods for analysing composite photoelectron spectra (curve fitting, deconvolution and spectral subtraction) are discussed and examined critically and the advantages of the ‘difference spectra’ approach highlighted. Evidence for variable oxidation states (suboxides) is obtained from an analysis of the Ti(2p) spectra observed during the formation of thin oxide films (ca. 10 Å). Angular-dependent studies established that the lower oxidation states Ti²⁺ and Ti³⁺ were formed preferentially at the metal–oxide interface, whereas Ti⁴⁺ species were dominant at the oxide–gas interface. The distribution of the oxidation states within the thin oxide overlayer may be altered by thermally induced diffusion of Ti⁰ species from the metal substrate; the latter can occur at low temperature (ca. 200 K) for the thin oxide film regime investigated.