Formaldehyde gas sensing studies of nanostructured ZnO thin films synthesised using spray pyrolysis

Zinc oxide thin film (ZnO) gas sensor is prepared by an inexpensive spray pyrolysis method on a pre-cleaned glass substrate using optimised deposition parameters. The structural, morphological, and chemical characteristics of the prepared film were investigated with XRD, TEM, FESEM, XPS, and Raman spectroscopy. The hexagonal wurtzite crystal structure of the synthesized ZnO particles was verified by X-ray diffraction (XRD) analysis. Using the Scherrer equation, the average crystallite size of the prepared sample was determined to be 21.9 nm. Raman spectroscopy, FESEM, and TEM analysis agreed with the XRD findings. The XPS analysis further confirms the presence and chemical composition of ZnO in the deposited thin film. Gas sensing properties of zinc oxide film were investigated with the static liquid distribution approach. The sensor was notably selective towards formaldehyde gas at ambient temperature and showed good stability, response and recovery characteristics of 60 and 25 s, respectively, after being subjected to 5 ppm of formaldehyde at room temperature. This proves that the ZnO thin film of high quality was successfully prepared for the detection toxic formaldehyde under ambient conditions.