XPS analysis of thin non-stoichiometric titanium oxide films

The present study focuses on the investigation of thin films of non-stoichiometric titanium oxide TiOx, which attract significant interest due to their unique physico-chemical properties and their applications in photocatalysis, protective coatings, electronics, and sensorics. The primary objective of the research was to determine the chemical composition and construct the concentration profiles of TiOx films using X-ray Photoelectron Spectroscopy (XPS) combined with ion etching techniques. However, the chemical composition analysis of transition metals oxides as a function of sample depth is complicated due to the ion-beam reducing of the surface oxides. This work proposes an XPS spectra processing technique that allows to reduce the influence of ion etching and restore the true concentration profile of TiOx. Magnetron sputtering was employed to fabricate thin TiOx films in environments with varying oxygen contents (1%, 3%, 5%). It was revealed that the surface of all samples oxidized to TiO2; however, it was established that the increase of the oxygen content in the working environment led to the growth of the proportion of Ti3+ and Ti2+ chemical states throughout the film bulk. To mitigate artifacts associated with ion etching, the modified layer thickness was simulated using the SRIM program; an approach was proposed based on comparing spectra obtained at different angles of photoelectron emission. The findings demonstrated that the TiOx_1% sample contained metallic titanium (Ti0), while the TiOx_3% and TiOx_5% films consisted of non-stoichiometric oxides, predominantly Ti2+ and Ti3+, respectively. The results demonstrate the possibility for establishing the original composition of TiOx films, which is crucial for controlling their functional properties across diverse applications. The developed method holds promise for characterizing other oxide systems susceptible to ion etching.