Influences of microstructure on hydrogen sulfide sensing characteristics of tin dioxide films

Three types of SnO2 films, screen printed (20 mu m thick, A), sputtered (20-500 nm, B) and SnO2 sol-derived (0.6 mu m, C), were found to have very different sensing properties to 5 ppm H2S in air. Films A and B showed sluggish response at 200 degrees C, increasing the response rate with incresing temperature accompanied by significant losses in sensitivity. On the other hand, him C showed sharp response as well as high sensitivity at 200 degrees C. As revealed from pore size distribution measurements, both A and B possessed a significant volume of micropores (less than 3 nm in diameter) while C possessed only mesopores (10-20 nm). These facts suggest that the difficulty of gas diffusion inside micropores is responsible for the sluggish response of films A and B at 200 degrees C, and that the development of large uniform mesopores leads to excellent H2S sensing characteristics of film C. Even with him C, however, the response was degraded to a lower intermediate concentration range of H2S (typically 0.1-1 ppm), suggesting that the gas diffusion inside mesopores becomes rate determining in that range.