## 1 Introduction  
For many years, researchers have been searching for chemical compounds with good electrical properties as well as transparency in the visible wavelength range. It seems that some selected metal oxides such as V\(\mathrm{{}_{x}}\)O\(\mathrm{{}_{y}}\), WO\(\mathrm{{}_{x}}\), In\(\mathrm{{}_{x}}\)O\(\mathrm{{}_{y}}\), Co\(\mathrm{{}_{x}}\)O\(\mathrm{{}_{y}}\) or Ti\(\mathrm{{}_{x}}\)O\(\mathrm{{}_{y}}\)[1; 2; 3] are able to meet such requirements. Vanadium can occur in numerous oxidation states, e.g., \(V^{5+}\), V\({}^{4+}\) or V\({}^{3+}\) which is advantageous for the preparation of thin films with different electrical and chemical properties for different applications [4]. Vanadium (di)oxide (VO\(\mathrm{{}_{2}}\)) is known for its semiconductor-to-metal transition behaviour, which occurs at a specific temperature. Below 68 \({}^{\circ}\)C VO\(\mathrm{{}_{2}}\) is monoclinic, while above this temperature its structure changes to tetragonal rutile [5]. This structure transformation is fully reversible and is matched by a change in the optical and electrical properties of VO\(\mathrm{{}_{2}}\). Such behaviour makes VO\(\mathrm{{}_{2}}\) suitable, for example, for thermochromic applications [6; 7]. V\(\mathrm{{}_{2}}\)O\(\mathrm{{}_{5}}\) and V\(\mathrm{{}_{2}}\)O\(\mathrm{{}_{3}}\) also exhibit a similar transition that occurs at temperatures of 250 \({}^{\circ}\)C and -120 \({}^{\circ}\)C, respectively [8]. Vanadium pentoxide (V\(\mathrm{{}_{2}}\)O\(\mathrm{{}_{5}}\)) is an n-type semiconductor with an optical band gap of 2.3 eV [9] and good thermal and chemical stability. It is used as a catalyst for chemical reactions [10]. Vanadia also has a potential application in chemoresistive gas sensors with oxidizing gases such as O\(\mathrm{{}_{2}}\)[11] or NO\(\mathrm{{}_{x}}\)[12] or with reducing gases such as ethanol [13] or ammonia [14]. The low resistivity and high temperature coefficient of resistance (TCR) suggest potential applications in the construction of microbolometers [15]. Other possible applications of vanadium oxides are in smart windows [16], optical switches [17], infrared sensors [18] or flexible electronic devices [19]. To date, many methods have been used to prepare vanadium oxide thin films, for example sol-gel, evaporation, molecular beam epitaxy, or sputtering [18]. Magnetron sputtering seems to be one of the most interesting technologies because of the possibility to produce large area thin films with repeatable properties. The deposition process may be conducted at a low substrate temperature. The control of process parameters such as pressure or gas flow ratio allows us to obtain a high deposition rate and thin films with predictable properties [15]. It should be noted that in comparison with other deposition methods, magnetron sputtering has many advantages, e.g., very good adhesion to the substrate [20]. In recent years, there have been various reports regarding the properties of vanadium oxide thin films. Researchers have mainly focused on one form of oxide or methods of deposition other than magnetron sputtering. For example, [PERSON] et al. [21] studied the thermochromic properties of vanadium dioxide (VO\({}_{2}\)) deposited by high-power impulse magnetron sputtering. The deposition process was carried out using various reactive and working gas ratios ranging from 10:1 to 100:1 for Ar:O\({}_{2}\). It should be noted that as-deposited thin films were further annealed at 500 \({}^{\circ}\)C for 3 min which resulted in formation of the crystalline structure. The addition of a TiO\({}_{2}\) buffer layer between VO\({}_{2}\) and the substrate caused an increase in crystallinity and a higher transparency of thin films. The authors showed that with the decrease in the Ar:O\({}_{2}\) ratio, the crystal phase changed from V\({}_{2}\)O\({}_{3}\) to VO\({}_{2}\) and finally to V\({}_{2}\)O\({}_{5}\)[PERSON] Furthermore, TEM investigations showed that as-deposited thin films became amorphous with lower Ar:O\({}_{2}\) gas ratios [21]. In turn, [PERSON] et al.