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| Tungsten oxide thin films have been deposited on alumina substrates by reactive radio frequency (rf) magnetron sputtering, following by annealed in air at 200, 300, 400, and 600 oC for 4 h. The effects of thermal annealing on the microstructure and gas sensing properties of the tungsten oxide thin films were studied. The surface morphology, microstructure and chemical composition of the annealed films were investigated by X-ray diffraction(XRD), field emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS) techniques. When raising the annealing temperature from 200oC to 400oC, the film tends to crystallize to triclinic structure from amorphous state, while higher temperature results in an increase in grain size and a shrinkage of structural pores. The film annealed at 400oC has lower O/W ratio than the one annealed at 600oC. The NO2-sensing properties of the annealed films were also evaluated, and the measurements revealed that the tungsten oxide film annealed at 400 oC has a quicker response/recovery and the highest sensitivity to 1ppm NO2 due to its loose and porous structure and small grain size. |
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| Keywords:tungsten oxide film; gas sensors; annealing; sensing properties |
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