## 3 Results and Discussion  
### Optical Properties  
The film deposited under oxygen-rich conditions (TiO\(\mathrm{x}^{\mathrm{ORC}}\)) was characterised by high transparency in the visible and near-infrared wavelength range (Figure 1). The transparency levels at \(\lambda\) = 550 nm and \(\lambda\) = 1550 nm were equal to 68% and 72%, respectively. Transmittance was found to decrease after annealing above 600 \({}^{\circ}\)C, mainly in the visible range. The reflectance of the sample did not change significantly after annealing. The absorption edge (\(\lambda_{\mathrm{cut-off}}\)) of the TiO\(\mathrm{x}^{\mathrm{ORC}}\) films increased with increasing annealing temperature (Figure 2). The optical band gap value was in the range of 2.0 to 2.1 eV and did not change significantly after annealing at temperatures up to 600 \({}^{\circ}\)C, while it decreased by 0.3 eV after annealing at 800 \({}^{\circ}\)C. These results are lower compared to those of stoichiometric TiO\({}_{2}\) (e.g., [5]), but are in agreement with parameters of insufficiently oxidised layers as shown by [PERSON] et al. [9]. The Urbach energy value (the width of the band tail) was equal to approximately 0.6 eV and did not change after annealing. The values of the mentioned parameters are listed in Table 1. Such changes in optical parameters are characteristic of oxide materials based on Ti. Similar conclusions can also be found in other works, e.g., by [PERSON] et al. [28], [PERSON] et al. [29], and [PERSON] et al. [18]. In turn, the film deposited under oxygen-deficient conditions (TiOX\({}^{\text{ODC}}\)) was characterised by a dark blue colour and very low transmittance directly after deposition, as well as after annealing at 100 \({}^{\circ}\)C in both the VIS and NIR regions (Figure 3). Furthermore, the transmission level at \(\lambda\) = 550 nm increased only to approximately 10% after annealing at a higher temperature. In the NIR range, after annealing at 200 \({}^{\circ}\)C, the transmittance at  
Figure 1: Influence of additional annealing on optical properties of TiOx thin films as deposited under oxygen-rich conditions (ORC): (**a**) transmittance in the VIS region, (**b**) transmittance in the NIR region, (**c**) reflectance in the VIS region, (**d**) transmittance and reflectance values at \(\lambda\) = 550 nm and \(\lambda\) = 1550 nm as a function of the annealing temperature. Figure 2: Determination of: (**a**) optical band gap (Eg\({}^{\text{opt}}\)), (**b**) Urbach energy (Eu\({}_{\text{d}}\)), (**c**) absorption edge (\(\lambda_{\text{cut-off}}\)) of TiOX\({}^{\text{ORC}}\) films as deposited under oxygen-rich conditions, and (**d**) calculated values of these parameters as a function of the annealing temperature. \(\lambda\) = 1550 nm increased to approximately 60% and did not change further with increasing temperature. The reflectance increased slightly after annealing at 200 \({}^{\circ}\)C and 300 \({}^{\circ}\)C and decreased again after annealing at a higher temperature. The change in absorption edge (\(\lambda_{\text{cut-off}}\)) also increased after annealing at 300 \({}^{\circ}\)C and did not change with further increases in the annealing temperature (Figure 4). The optical band gap value was equal to 0.7 eV for the sample annealed at 200 \({}^{\circ}\)C, and decreased with an increasing annealing temperature to a value of 0.3 eV. It should be admitted that such low values result from low transparency and correspond to the metallic characteristic of these films. In our opinion, they should only be considered indicative. The width of the band tail also decreased after annealing at 300 \({}^{\circ}\)C. The values of the parameters mentioned above are collected in Table 2. Summarising these results, it can be stated that the described changes indicate a low amount of oxygen in those films and their semi-metallic character. Even additional annealing at 800 \({}^{\circ}\)C did not result in higher oxidation, which would lead to much higher transparency.