## 3 Results  
Reactive magnetron sputtering under Ar-O\({}_{2}\) atmosphere produced a colorless transparent film (sample A) consisting of anatase and rutile TiO\({}_{2}\) phases (Figure 1). When the gas mixture was supplemented with hydrogen, the crystallinity of the samples started to weaken, and they started to gain a noticeable tint. At the largest hydrogen concentration (sample B3), the effect was especially strong: the sample nearly lost the rutile phase and obtained a dark blue-grey shade. Traditionally, the appearance of blueish shade in titanium oxide samples is associated with Ti\({}^{4+}\) reduction to Ti\({}^{3+}\) and observation of Ti\({}_{2}\)O\({}_{3}\) phase [18; 19]. However, during close inspection of TiHO XRD patterns (Figure 1), we did not detect any features that could be attributed to Ti\({}_{2}\)O\({}_{3}\) or any other titanium suboxides. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Samples** & **Ar Flux** & **O\({}_{2}\) Flux** & **H\({}_{2}\) Flux** & **Ar:O\({}_{2}\):H\({}_{2}\) Flux Ratio** & **Total Pressure** & **Power Source** \\ \hline A & 4.5 sccm & 1.2 sccm & - & 3.78:1:- & 6 \(\times\) 10\({}^{-3}\) mbar & 300 W p-DC \\ B1 & 2.7 sccm & 6.4 sccm & 15.1 sccm & 0.42:1:2.36 & 6 \(\times\) 10\({}^{-3}\) mbar & 300 W DC \\ B2 & 2.8 sccm & 4.2 sccm & 20.1 sccm & 0.67:1:4.78 & 6 \(\times\) 10\({}^{-3}\) mbar & 300 W DC \\ B3 & 2.8 sccm & 3.6 sccm & 22.5 sccm & 0.78:1:6.25 & 6 \(\times\) 10\({}^{-3}\) mbar & 300 W DC \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main parameters of reactive magnetron sputtering deposition process. Figure 1: Visual appearance (insert) and XRD patterns of TiO\({}_{2}\) (**A**) and TiHO (**B1–B3**) samples. These results are interesting from several perspectives. First, earlier reports demonstrated that Ti-O-H interaction during TiH\({}_{2}\) powder oxidation experiments nearly exclusively results in direct or indirect (i.e., through the intermediate phases of titanium suboxides) formation of the rutile TiO\({}_{2}\)[10; 15; 20]. Naturally, the processes of TiH\({}_{2}\) oxidation and titanium sputtering in a reactive Ar-O\({}_{2}\)-H\({}_{2}\) atmosphere have fundamental differences and can not be compared directly. Still, the observed decline in the crystallinity of the thermodynamically most stable rutile TiO\({}_{2}\) phase is not a trivial outcome and supports the indications by other groups [21; 22], who suggested that products of Ti-O-H interaction can be method-specific. Second, in defected TiO\({}_{2}\) samples (including some \"black TiO\({}_{2}\)\" samples produced using hydrogen [23]) the dark color is commonly attributed to the presence of oxygen vacancies and Ti\({}^{3+}\) species [24; 25; 26]. For example, a similar trend of TiO\({}_{2}\) darkening and rutile phase depreciation from the initial anatase-rutile mixture was observed when standard white TiO\({}_{2}\) powders were reduced by NaBH\({}_{4}\)[27]. In that study, XPS analysis of reduced TiO\({}_{2}\) powders confirmed that color and structural changes of the initial TiO\({}_{2}\) powders can be attributed to the propagation of oxygen vacancies (indicated by the decrease in bulk O:Ti ratio) and partial reduction of Ti\({}^{4+}\) to Ti\({}^{3+}\) state (indicated by the appearance of the additional Ti 2p\({}_{3/2}\) peak component at approximately 457.1 eV). In order to resolve the discrepancy between the supposed (by the color) and observed crystal structure of TiHO samples, we also used the XPS technique and determined the chemical state of titanium. If it were present, Ti(III) oxide (i.e., Ti\({}^{3+}\)) should have an O 1s peak component at approximately 532.5 eV and Ti 2p peak components at 457.3 eV and 462.5 eV [28; 29]. Moreover, looking at the color changes of the TiHO samples, one might expect that peak components related to Ti(III) oxide should become stronger proceeding from sample B1 to sample B3.