WO/sub 3/ thin films prepared by the sol-gel process for ozone sensing

Tungsten trioxide (WO₃) thin films have been prepared by the sol-gel process and their ozone sensing properties. The morphology, microstructure, crystalline structure and chemical composition of the thin films have been analysed using SEM, XRD and RBS techniques. SEM analysis showed that WO₃ thin films annealed at 500°C are smooth and uniform with a grain size of 20-50 nm, above which microcracking observed in the films. The WO₃ films annealed up to 400°C are amorphous, while annealing at 500°C and above, resulted in the formation of monoclinic WO₃ polycrystalline structure with (200) preferential orientation. RBS results have revealed that the films annealed at 400°C are stoichiometric, above which the films turned to off-stoichiometric. The electrical resistance of the thin films annealed at 500°C increased 18 times when it exposed to 175 ppb O₃ compared to the air exposure with a response time of 1-2 min. The details of the structural and microstructural analysis of the films and their effects on the sensing properties are discussed