Yellow tungsten oxide, or tungsten trioxide or WO3, is often applied to NOx gas sensor in form of a thin film. For example, some experts have deposited WO3 thin films by reactive RF sputtering onto low-cost glass substrates as gas sensitive coating.
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And the experts have investigated the properties of the grown films by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) in order to characterize their structure, composition, surface chemistry. The D.C. electrical response to different gases of the WO3 thin films has been measured in the temperature range from 100 to 400°C showing an increase of electrical resistance with a good sensitivity towards NOx gas at 250°C. WO3 thin films oppositely detect also NH3, H2, H2S, SO2 gases by decreasing the electrical resistance and are practically insensitive to interfering gases like CO, CH4 in the same temperature range. The sensing characteristics of the NOx gas detector based on yellow tungsten oxide thin films are reported.
