Double-Angle X-ray Photoelectron Spectroscopy Depth Profiling of Nonstoichiometric TiOx Thin Films with Resistive Switching Behavior

The nonstoichiometric titanium oxide TiOx is a promising material for memristive devices, where its resistive switching properties are governed by structural and chemical state variations, particularly the proportion between the Ti(IV), Ti(III), and Ti(II) components. While X-ray photoelectron spectroscopy (XPS) is widely employed for chemical state analysis, conventional XPS depth profiling is limited by ion beam-induced reduction artifacts. The double-angle XPS depth profiling proposed in this paper allows one to determine the elemental composition and chemical state of titanium atoms of TiOx thin films as a function of sample depth while excluding the contribution from the damaged surface. Using this approach, we investigate the films of nonstoichiometric titanium oxides obtained by magnetron deposition in a medium with different oxygen contents (1, 3, and 5%), which exhibit different resistive switching behaviors. Based on the current–voltage characteristics measured by means of the conducting probe of an atomic-force microscope (AFM) in the contact mode, it is shown that, as the oxidation level of the film increases, so does its resistance and switching voltage. Due to atmospheric humidity, the anodic polarization of the sample leads to the oxidation of the metallic component and the Ti(II) and Ti(III) components of the film.