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Tungsten trioxide (WO3) is a wide-bandgap semiconductor. Its advantages include highchemical stability and low price. Furthermore, WO3 has chromogenic properties, that is, the abilityto switch between pale yellow and dark blue in response to various stimuli, including temperature,light irradiation, electric field, and exposure to hydrogen. Due to its high colouring efficiency andfast switching, it can be used in antidazzling mirrors and smart window applications, as well as in gassensing. In this paper, we present the influence of annealing on the properties of WO3 coatings that wereannealed at temperatures in the range from 200C to 400C. The sensing response was characterisedbased on the transmittance measurement during exposure to air and Ar/H2 mixture with hydrogenconcentrations from 25 ppm to 1000 ppm. Furthermore, the influence of annealing on the structureand morphology of the coatings was examined. Annealing at 400C led to a structure change fromamorphous to crystalline one. After the introduction of the Ar/H2 mixture, a decrease in transmittancewas observed for all of the analysed coatings. For films annealed at 200C and 300C, the transmittancevalue decreased during the entire colouring cycle, while for the coating annealed at 400C a plateau wasreached after 7 minutes of exposure. It was found that the best sensing characteristics were obtained forthe WO3 thin film annealed at 400C due to high sensor response to very low hydrogen concentrations(SR = 6.3 for 25 ppm H2) as well as short response and recovery times.Keywords: electronics, tungsten oxide, thin film, gas impulse magnetron sputtering, gas sensingproperties

This work describes the influence of the annealing temperature on the optical and surfaceproperties of non-stoichiometric titanium oxide (TiOx) thin films. The results were related to theinvestigation of the sensing response toward H2 gas. The samples were prepared by the magnetronsputtering method using Ar:O2 plasma with low oxygen content (20% and 30%). An increase in theamount of oxygen in the gas mixture supplied to the magnetron led to a decrease in the deposition rate.The thickness of the deposited thin films, determined by the use of an optical profiler, was found tobe 600 nm and 200 nm, respectively. The coatings were then annealed in an ambient air atmosphereat a temperature in the range from 100C to 800C. Additionally, the roughness of the coating surfacewas measured. To investigate the optical properties of the thin films, transmission and reflection spectrawere measured, and parameters such as transmission coefficient, cutoff wavelength value, and opticalband gap value were determined as functions of the annealing temperature. The sensing propertiesof the thin films were characterised on the basis of changes in a resistance value as a response to amix of Ar:3.5% H2. It was found that the oxidation of the thin films has a key influence not only onthe response time of the TiOx thin films, but also on the character of the response.Keywords: materials engineering, titanium oxides, thin films, magnetron sputtering, optical properties,gas sensing properties

TiOx films were prepared by gas impulse magnetron sputtering under oxygen-deficient (ODC) and oxygen-rich conditions (ORC) and annealing at 100–800 °C was used. The O2 content had an effect on their transparency level (Tλ). The films from the ORC mode had ca. Tλ = 60%, which decreased slightly in the VIS range after annealing. The film from the ODC mode had lower transmission (ca. gopt) and Urbach energy (Eu) were also observed. The deposition parameters had an influence on the microstructure of TiOx coatings. The ORC and ODC modes resulted in columnar and grainy structures, respectively. Directly after deposition, both coatings were amorphous according to the GIXRD results. In the case of TiOxORC films, this state was retained even after annealing, while for TiOxODC, the crystalline forms of Ti and TiO2-anatase were revealed with increasing temperature. Sensor studies have shown that the response to H2 in the coating deposited under oxygen-rich conditions was characteristic of n-type conductivity, while oxygen-deficient conditions led to a p-type response. The highest sensor responses were achieved for TiOxODC annealed at 300 °C and 400 °C.