H 2 S gas sensing mechanism of SnO2 films with ultrathin CuO dotted islands

${\mathrm{H}}_2\mathrm{S}$ gas interaction mechanisms of sputtered ${\mathrm{SnO}}_2$ and ${\mathrm{SnO}}_2–\mathrm{CuO}$ bilayer sensors with a varying distribution of the Cu catalyst on ${\mathrm{SnO}}_2$ are studied using Pt interdigital electrodes within the sensing film. Sensitivity to ${\mathrm{H}}_2\mathrm{S}$ gas is investigated in the range 20–1200 ppm. Changes induced on the surface, the ${\mathrm{SnO}}_2–\mathrm{CuO}$ interface, and the internal bulk region of the sensing ${\mathrm{SnO}}_2$ film upon exposure to ${\mathrm{H}}_2\mathrm{S}$ have been analyzed to explain the increasing sensitivity of three different sensors ${\mathrm{SnO}}_2,$ ${\mathrm{SnO}}_2–\mathrm{CuO},$ and ${\mathrm{SnO}}_2$ with CuO islands. ${\mathrm{SnO}}_2$ film covered with 0.6 mm diameter ultrathin (∼10 nm) CuO dots is found to exhibit a high sensitivity of ${\text{7.3×10}}^3$ at a low operating temperature of 150 °C. A response speed of 14 s for 20 ppm of ${\mathrm{H}}_2\mathrm{S},$ and a fast recovery time of 118 s in flowing air have been measured. The presence of ultrathin CuO dotted islands allow effective removal of adsorbed oxygen from the uncovered ${\mathrm{SnO}}_2$ surface due to spillover of hydrogen dissociated from the ${\mathrm{H}}_2\mathrm{S–CuO}$ interaction, and the spillover mechanism is sensed through the observed fast response characteristics, and the high sensitivity of the ${\mathrm{SnO}}_2–\mathrm{CuO}$ -dot sensor.