Comparative analysis of physico-chemical and gas sensing characteristics of two different forms of SnO2 films

In turn XPS studies confirm that for both SnO2 samples a slight nonstoichiometry with a relative [O]/[Sn] concentration of 1.8, and slightly different amount of C contamination at the surface of internal grains with relative [C]/[Sn] concentration of 3.5 and 3.2, respectively. This undesired C contamination cannot be ignored because it creates an uncontrolled barrier for the potential gas adsorption at the internal surface of sensor material. This is confirmed by the gas sensor response in NO2 atmosphere of both SnO2 samples because the sensitivity is evidently smaller for RGTO SnO2 with respect to the L-CVD SnO2 samples, whereas the response time showed a completely opposite tendency. It is probably caused by the smaller extension of internal surface and grain dimension with respect to the Debye length, as well as higher C contamination observed for RGTO SnO2 with respect to L-CVD SnO2 samples.