Characterization and hydrogen gas sensing properties of TiO2 thin films prepared by sol–gel method

Thin films of titanium dioxide with thickness of about 150 nm were deposited by spin coating method on a sapphire substrate from a sol–gel and annealed at various temperatures (from 600 °C to 1000 °C). Structural, optical and hydrogen gas sensing properties of the films were investigated. The annealing temperatures from 600 to 800 °C led to anatase phase with grain size in the range of 14–28 nm. Further increase of the annealing temperature resulted in transformation to rutile phase with larger grain size of about 100–120 nm. The optical band gap tended to decrease with increasing annealing temperature. The estimated values of activation energy for charge transport were in the range of 0.6–1.0 eV for films annealed at temperatures from 600 °C to 800 °C and 0.37–0.38 eV for films annealed at 900 °C and 1000 °C. The films annealed at 900 °C and 1000 °C showed better hydrogen sensitivity, what can be at least partially caused by their higher surface roughness.