Characterization of sol-gel prepared WO3 thin films as a gas sensor (original) (raw)

1999, Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

Tungsten trioxide (WO 3) thin films have been prepared by the sol-gel process and annealed at different temperatures of 400, 500, 600, and 700°C for 1 h. The morphology, microstructure, crystalline structure, and composition of the films have been analyzed using scanning electron microscopy ͑SEM͒, x-ray diffraction, Rutherford backscattering spectroscopy ͑RBS͒, and x-ray photoelectron spectroscopy ͑XPS͒ techniques. The SEM analysis showed that the films annealed at 400°C are smooth and uniform. However, these evolved as granular at an annealing temperature of 500°C. The films annealed at still higher temperatures have two distinct grains of different shapes and sizes. The films annealed below 400°C are amorphous. Annealing at 500°C resulted in the films having polycrystalline structure. RBS and XPS characterization have revealed that the films annealed at 400°C are stoichiometric. Annealing above this temperature resulted in the films becoming off-stoichiometric. The electrical resistance of the films annealed at 500°C increased 18 times when exposed to 175 ppb O 3 gas compared to the air exposure, with the response time being as short as 1-2 min.