Influence of Annealing on Gas-Sensing Properties of TiOx Coatings Prepared by Gas Impulse Magnetron Sputtering with Various O-2 Content

TiOx films were prepared by gas impulse magnetron sputtering under oxygen-deficient (ODC) and oxygen-rich conditions (ORC) and annealing at 100-800 degrees C was used. The O-2 content had an effect on their transparency level (T-lambda). The films from the ORC mode had ca. T-lambda = 60%, which decreased slightly in the VIS range after annealing. The film from the ODC mode had lower transmission (ca. <10%), which increased in the NIR range after annealing by up to ca. 60%. Differences in optical band gap (E-g(opt)) and Urbach energy (E-u) 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 TiOx(ORC) films, this state was retained even after annealing, while for TiOx(ODC), the crystalline forms of Ti and TiO2-anatase were revealed with increasing temperature. Sensor studies have shown that the response to H-2 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 TiOx(ODC) annealed at 300 degrees C and 400 degrees C.