## 3 Results and Discussion
### Optical Properties  
The optical properties of the V\({}_{x}\)O\({}_{y}\) thin films were examined on the basis of the transmission characteristics shown in Figure 3. A higher oxygen content in Ar:O\({}_{2}\) gas ratios during sputtering caused an increase in the average transmission coefficient in the visible wavelength range. The characteristics of films prepared with the Ar:O\({}_{2}\) ratios of 2:1 and 3:1 are almost overlapped, i.e., the average transmission is c.a. 2% higher for the sample prepared with a higher oxygen content. Moreover, these films had the same thickness of 325 nm and were transparent. A decrease in oxygen content in the gas mixture during sputtering caused a further decrease in the transparency of the thin films. The dependence of the average transmission determined in the visible wavelength range on the Ar:O\({}_{2}\) gas ratio is presented in Figure 4. It was calculated using the integral of each transmission characteristic in the range of 380 nm to 760 nm. The average transmission values are almost the same for three sets of thin films prepared with the highest oxygen content and range between 48.6% and 51.1%. The decrease in oxygen in the gas atmosphere during the deposition process caused the decrease in average transmission to 36.2% and 39.1% for samples deposited with 6:1 and 5:1 Ar:O\({}_{2}\), respectively. A further decrease in the O\({}_{2}\) content in the gas mixture during magnetron sputtering caused the decrease in the average transmission values to 21.8% and 24.5% (Figure 4, Table 1). According to the  
Figure 2: Diffraction patterns of vanadium oxides deposited with various Ar:O\({}_{2}\) gas ratios. literature, similar research on vanadium oxides was conducted by [PERSON] et al. [31], who studied V\({}_{x}\)O\({}_{y}\) thin films deposited with different oxygen partial pressure and substrate temperature during the deposition process. They showed that thin films prepared at room temperature with low oxygen partial pressure (from 0.5 to 1%) had a yellow to dark green colour and were amorphous, as observed in this work. Other authors, e.g., [PERSON] et al. [32], compared V\({}_{2}\)O\({}_{5}\) with different thicknesses of 320, 550 and 700 nm and showed that thicker films had lower transmission coefficients, i.e., 73%, 58% and 45%, respectively [32]. [PERSON] et al. [33] focused on the vanadium oxide examination by comparing various thicknesses and oxygen partial pressure during the magnetron sputtering process. They found that a higher oxygen partial pressure resulted in a higher transmission rate, and that a change of three orders caused an increase from approximately 62% to 78%. Furthermore, a higher transmission was observed once more for thinner thin films [33]. [PERSON] et al. examined the influence of V\({}_{2}\)O\({}_{5}\) grain size on the transmission coefficient and reported values in the range of 66% to 75%, where higher grain size resulted in lower transmission [34]. Figure 3: SEM images of the surface morphology of vanadium oxide thin films deposited with various Ar:O\({}_{2}\) gas ratios: (**a**) 2:1, (**b**) 3:1, (**c**) 4:1, (**d**) 5:1, (**e**) 6:1, (**f**) 7:1, (**g**) 8:1 and (**h**) an EDS spectrum of a thin film deposited with Ar:O\({}_{2}\) ratio of 4:1. The fundamental absorption edge was calculated from the transmission spectra. The values are red-shifted with the higher O\({}_{2}\) content in the sputtering atmosphere (Figure 5). The values of \(\lambda_{\text{cut-off}}\) range between 371 and 470 nm (Table 1). [PERSON] et al. [35] reported the fundamental absorption edge at about 600 nm, while other authors reported values between 460 and 550 nm [36, 37, 38, 39] for amorphous V\({}_{2}\)O\({}_{5}\) thin films prepared using magnetron sputtering. Additionally, the optical band gap energy (E\({}_{\text{g}}\)) was calculated using Tauc plots (Figure 6) [31, 40]. The values did not vary significantly and were in the range between 1.91 and 2.08 eV.