Influence of multilayer deposition on characteristics of nanocrystalline SnO2 thin films produce by sol-gel technique for gas sensor application

Nanocrystalline SnO2 thin films have been prepared on glass substrates using sol-gel dip-coating technique. The deposited films were annealed in air at 500 °C for one hour. Structural, optical, electrical, and sensing properties of the films were studied for different number of layers. X-ray diffraction spectra reveal the polycrystalline nature of the SnO2 films with tetragonal crystal structure, and have preferred growth direction along (110). The crystallite size of the thin films increased with increasing number of layers. AFM and SEM results indicated that the average grain size increased as number of layers increased. The optical band gap energy and transmittance of dip-coated films decreased as number of layers increased. The electrical properties of SnO2 films include DC electrical conductivity, showing that the films have two activation energies, namely, Ea1 and Ea2, which increase as number of layers increases. The films were further investigated in terms of their sensing abilities for carbon monoxide (CO) and nitrogen dioxide (NO2) gases at 50 ppm by measuring their sensitivity to these gases at different times and temperatures. Our results demonstrated that dip-coated prepared films were highly sensitive to CO and NO2 at 200 °C.