The WO3 thin films have been synthesized on to the glass substrates by a simple and easy spin coating method at different deposition cycles and their sensor responses towards various concentrations of NO2 gas were investigated. The WO3 films were spin coated at a spinning rate of 2500–3000 rpm for 5, 10 and 15 deposition cycles, respectively. Then the films were annealed at 400 °C for 1 h in a furnace. The structural, morphological, optical and electrical properties of WO3 films were studied by different characterization techniques such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), FT-RAMAN Spectroscopy and electrical resistivity measurements by laboratory made two probe method respectively. It reveals a spherical grain – like morphology with a pure monoclinic phase of WO3. The FT-RAMAN spectra also confirm the pure monoclinic phase of WO3. The WO3-10 film sensor exhibits maximum gas sensitivity 21.93 and 102.4% to 5 and 100 ppm NO2 at 200 °C, respectively. The WO3-10 thin film sensors is highly sensitive and selective to NO2 over other gases.
Rapid NO2 gas sensor has been developed based on PbS nanoparticulate thin films synthesized by Successive Ionic Layer Adsorption and Reaction (SILAR) method at different precursor concentrations. The structural and morphological properties were investigated by means of X-ray diffraction and field emission scanning electron microscope. NO2 gas sensing properties of PbS thin films deposited at different concentrations were tested. PbS film with 0.25 M precursor concentration showed the highest sensitivity. In order to optimize the operating temperature, the sensitivity of the sensor to 50 ppm NO2 gas was measured at different operating temperatures, from 50 to 200 °C. The gas sensitivity increased with an increase in operating temperature and achieved the maximum value at 150 °C, followed by a decrease in sensitivity with further increase of the operating temperature. The sensitivity was about 35 % for 50 ppm NO2 at 150 °C with rapid response time of 6 s. T90 and T10 recovery time was 97 s at this gas concentration.