Hydrogen sulfide sensing characteristics of tin oxide sol-derived thin films

Porous thin films of SnO₂ were prepared on an alumina substrate using hydrothermally synthesized SnO₂ sol, to investigate the influences of film-preparation conditions on the microstructure and H₂S sensing characteristics of the thin films obtained. The sensitivity and response transient to 5 ppm H₂S in air depended significantly on calcination temperature, operating temperature and film thickness. The 0.6 μm-thick SnO₂ film calcined at an optimum temperature of 700°C exhibited gas sensitivity (the ratio of electrical resistance in air to that in gas) as high as 550 together with good response transient characteristics to 5 ppm H₂S in air at 200°C. The crystallite size of SnO₂ as well as the pore size increased uniformly with a rise in calcination temperature, growing to 17.4 nm and 21 nm, at 700°C, respectively. The formation of well-defined large mesopores appears to be responsible for the excellent H₂S sensing characteristics.