Nanostructured Zinc Oxide Thin Films for NO_2 Gas Sensing

摘要

In this work, thin ZnO films were grown on glass substrates using the spray pyrolysis method. The deposited ZnO films were investigated by X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM). XRD patterns show that ZnO has a polycrystalline structure with a preferential growth orientation along the c-axis (002) plane. The mean crystallite size dimension estimated from XRD patterns was found to be around 65 nm. AFM images showed that ZnO films are composed of uniformly distributed ZnO nanocrystallites forming granular, rough and porous structure. The crystallite size dimension estimated from AFM images is in the 30-70 nm range, which is in agreement with that obtained from XRD. The features of these films were found to be suitable for sensing toxic gases such as NO_2. For this purpose the electrical response of the ZnO films were measured under constant air flow at various NO_2 concentrations. The ZnO films-based sensor was found to have fast and high response with an acceptable recovery delay, at relatively low working temperature (210℃) for NO_2 concentration ranging from 5 ppm to 200 ppm. Stable and rather satisfactory recovery delay ZnO-based sensor having reproducible response was pointed out at an operating temperature of 210℃.