Semiconductor TiO2–Ga2O3 thin film gas sensors derived from particulate sol–gel route

Abstract Nanostructured and mesoporous TiO 2 –Ga 2 O 3 thin films with various Ti:Ga atomic ratios were prepared by a new straightforward particulate sol–gel route. Titanium isopropoxide and gallium (III) nitrate hydrate were used as precursors, and hydroxypropyl cellulose (HPC) was used as a polymeric fugitive agent (PFA) in order to increase the specific surface area (SSA). XRD and TEM analysis of the powders revealed that the Ga 2 O 3 formed from the nitrate precursor retarded anatase-to-rutile transformation, crystallization and crystal growth. The average crystallite size of pure TiO 2 powder annealed at 600–1000 °C were in the range 4–10 nm; the values that could be decreased to 2–6 nm for TiO 2 –Ga 2 O 3 powders. Furthermore, one of the highest SSA was obtained by introducing Ga 2 O 3 into TiO 2 , being 305 m 2 g −1 for TG11 (Ti:Ga = 50:50 atomic ratio) binary oxide annealed at 600 °C. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO and NO 2 gases at low operating temperature of 200 °C, resulting in increased thermal stability of sensing films as well as a decrease in their power consumption. TG11 sensor showed the highest response towards all CO and NO 2 concentrations operated at 200 °C. The response magnitude of 13.7 and 4.3 with response times of 30 s and 108 s were achieved for TG11 sensor towards 400 ppm CO and 10 ppm NO 2 , respectively. Furthermore, calibration curves revealed that TiO 2 –Ga 2 O 3 sensors follow the power law ( S = A [ gas ] B ) (where S is sensor response, coefficients A and B are constants and [ gas ] is gas concentration) for the two types of gases, and they have excellent capability for the detection of low gas concentrations (25 ppm CO and 0.5 ppm NO 2 ). The maximum response of TiO 2 –Ga 2 O 3 sensors towards CO and NO 2 was measured at 450 and 400 °C, respectively. The sensor response decreased with increasing film annealing temperature owing to sintering of the particles. The response magnitude and response time of the sensors obtained in this work is superior to TiO 2 -based sensors reported in previous studies.