Influence of annealing on microstructure and NO2-sensing properties of sputtered WO3 thin films

Abstract The influences of thermal annealing on the microstructure and NO 2 -sensing properties of sputtered WO 3 thin films were investigated. The WO 3 films as-deposited at room temperature were amorphous and would crystallize to monoclinic structure when annealed at 350 °C or above. The grains and pores in the WO 3 films grew larger with an increase in annealing temperature. The effective surface area and pore volume changed non-monotonously with increasing the annealing temperature. The film annealed at 350 °C showed the largest effective surface area. The film annealed at 500 °C had the largest pore volume. Among the films investigated in this study, the WO 3 thin film annealed at 500 °C showed the quickest response/recovery and the highest response to 10 ppm NO 2 . These results indicate the importance of achieving porous structure on improving the gas sensing performance.

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