Enhanced catalytic activity of ultra-thin CuO islands on SnO2 films for fast response H2S gas sensors

Trace level detection of H₂S is of immense interest in diverse fields ranging from gas and oil exploration to dentistry. In the present work 0.12 μm thick sputtered SnO₂ films, and a novel SnO₂-CuO bilayer structure consisting of ultra thin (∼10 nm) CuO dotted islands (0.6 mm diameter) are investigated for H₂S gas sensing. With the SnO₂-CuO-dotted sensor, a high sensitivity of 7.3×10³ at a low operating temperature of 150°C is obtained with a fast response time of 14 seconds for 20 ppm of H₂S gas and a recovery time of 118 seconds under flowing air have been measured. The electronic and chemical interactions of the CuO catalyst layer on SnO₂ in the presence of H₂S have been analyzed in the light of space charge regions formed due to distributed p-type CuO islands on the n-type SnO₂ thin film surface. Dissociated hydrogen available from the CuO-H₂S interaction spills over and is found to be primarily responsible for the observed fast response characteristics.