Hydrogen sulfide gas sensing properties of thin films derived from SnO2 sols different in grain size

Sols of crystalline SnO2 with different mean grain (crystallite) sizes between 6 and 16 nm were prepared by subjecting stannic acid gel to hydrothermal treatments under various conditions. Thin film sensor devices with different film thicknesses between 200 and 900 nm were fabricated to investigate sensing properties to H2S gas. It was found that the sensor response to H2S, defined as the ratio of resistance in air to that in H2S-containing air, was greatly enhanced with decreasing film thick and with increasing grain size up to 16 nm, as expected from the gas diffusion-reaction theory. The response was surprisingly large, exceeding 104 at 150 °C, for the device deposited with a 200 nm-thick film of SnO212 nm in grain size.