Searching for the Formation of Ti-B Bonds in B-Doped TiO2-Rutile

Surface B-doped TiO2-rutile (110) single crystals obtained through different approaches have been characterized by X-ray photoelectron spectroscopy (XPS), and their thermal stability investigated. The thermal decomposition of dimethylaminoborane on the clean TiO2(110) surface, both stoichiometric and understoichiometric (Ar+ sputtered), leads to a complete B oxidation to B2O3, which segregates from the TiO2. B-ion implantation (using B2H6 as a source) has allowed us to obtain both B2O3 and interstitial B doping, which is stable at high temperature. Two further methods were developed to deposit B in a titanium-rich surface, either by reactive Ti evaporation in B2H6 or by dosing B2H6 on a thin Ti overlayer. In both cases, Ti-B bonds were formed, due to the creation of substitutional B and boride-like compounds, but after a thermal treatment, they converted into B-O bonds, demonstrating that, in all cases, the system tends to evolve to the most stable species (B2O3). The reported XPS data represent useful benchmarks to characterize B-doped titania materials.