Surface chemistry of ion beam modified native titania/Ti interfaces examined using X-ray photoelectron spectroscopy

It is often assumed in X-ray Photoelectron Spectroscopy that binding energy shifts are synonymous with changes in the chemical state of an atom and the chemical state can be described in terms of oxidation state and stoichiometry of the elements in a material that correlates with photoemission peaks. However, when an atom is bonded into a crystal lattice, the shapes and binding energy of photoemission may not match the expected stoichiometry when measured by XPS, even though shifts in binding energy suggest new oxidation states. In this work, a set of experiments is presented, in which Ar+ and He+ ions of different energies modify the native oxide on a titanium foil which yields XPS spectra that are not easily open to analysis by conventional peak models. In the course of analyzing these complex photoemission data by linear algebraic methods, the prospect emerged that XPS is suggesting that sputtering a native oxide may be providing insight into structural perturbation in addition to the stoichiometry-type changes to the native oxide.