## 3 Results and Discussion
### Electrical Properties  
The current-voltage characteristics of the selected thin films recorded in a planar configuration using alumina substrates containing interdigitated electrodes are shown in Figure 7. These thin films were selected due to their resistance change in relation to the other samples, and more precisely, the Ar:O\({}_{2}\) gas ratios for which there was a more visible change in resistance of the films. All the graphs show the linear dependence of current and voltage, which indicates the ohmic behaviour of prepared thin films. The slope of the relationship changes with changes in the resistance of the thin films; i.e., it was greater for the thin films deposited with less oxygen in the gas mixture during sputtering, meaning that these films are less resistive. The resistivity as a function of temperature is shown in Figure 8. The resistivity values decrease as the temperature increases for each deposited vanadium oxide. The highest resistivity was obtained for the sample prepared with the 2:1 Ar:O\({}_{2}\) gas ratio during the deposition process. The decrease in oxygen content in the sputtering atmosphere caused a three-fold decrease in resistivity values for samples deposited with Ar:O\({}_{2}\) of 8:1. Similar examinations were conducted by [PERSON] et al. [46], who compared vanadium oxides deposited with different oxygen flow rates and duty cycles. It was shown that the resistivity of the samples increases with an increase of the O\({}_{2}\) flow rate. Furthermore, the authors observed that the morphology, the deposition rate, and the electrical properties strongly depend on the oxygen content during the deposition process [46]. Figure 5: Results of (**a**) the determination of the fundamental absorption edge on a sample prepared with 2:1 Ar:O\({}_{2}\) gas ratio during magnetron sputtering and (**b**) dependence of the fundamental absorption edge on the Ar:O\({}_{2}\) gas ratio during sputtering. Figure 6: The fundamental absorption edge of as-deposited vanadium oxide thin films. Figure 7: Current-voltage characteristics of selected V\({}_{\rm x}\)O\({}_{\rm y}\) thin films prepared with Ar:O\({}_{2}\) gas ratios of: (**a**) 3:1, (**b**) 7:1 and (**c**) 8:1. The activation energy (\(E_{a}\)) was calculated for each sample based on the Arrhenius law (2) and linearly-fitted slopes of the resistivity as a function of the temperature plots, using the following equation [48]:  
\[\rho=\rho_{0}exp\left(\frac{E_{a}}{kT}\right) \tag{2}\]  
where \(k\) is the Boltzmann constant and \(T\) is the absolute temperature. The thermal activation energy has the lowest value (0.144 eV/K) for V\({}_{x}\)O\({}_{y}\) film prepared with the 8:1 Ar:O\({}_{2}\) gas ratio. The \(E_{a}\) values calculated for the remaining thin films were almost the same, ranging between 0.209 and 0.219 eV/K. Similar results were obtained by [PERSON] et al. [49] for the V\({}_{2}\)O\({}_{5}\) measured in the temperature range between 50 and 100 \({}^{\circ}\)C. The authors stated that as-deposited vanadium pentoxide was amorphous and had two ranges of thermal activation energy for the temperatures of 25-50 \({}^{\circ}\)C and 50-100 \({}^{\circ}\)C, which related to the thermal activation of electrical charge carriers into the conduction band and the change in the number of charge carriers in the conduction band, respectively. The optical energy gap was shown to affect electrical properties, such as the activation energy of V\({}_{2}\)O\({}_{5}\) deposited with pulsed DC magnetron sputtering [49]. The dependence of the resistivity and sheet resistance of vanadium oxide thin films on the Ar:O\({}_{2}\) gas ratio during the deposition process is presented in Figure 9. Both resistivity and sheet resistance increase with increasing amounts of oxygen in the Ar:O\({}_{2}\) gas mixture. The values are in the range of 9.10 to 2.04\(\cdot\)10\({}^{3}\)\(\Omega\)cm. Analogous results were obtained by [PERSON] et al.