Enhanced catalytic activity of ultra-thin CuO islands on SnO/sub 2/ films for fast response H/sub 2/S gas sensors

Trace level detection of H/sub 2/S is of immense interest in diverse fields ranging from gas and oil exploration to dentistry. In the present work 0.12 /spl mu/m thick sputtered SnO/sub 2/ films, and a novel SnO/sub 2/-CuO bilayer structure consisting of ultra thin (/spl sim/10 nm) CuO dotted islands (0.6 mm diameter) are investigated for H/sub 2/S gas sensing. With the SnO/sub 2/-CuO-dotted sensor, a high sensitivity of 7.3/spl times/10/sup 3/ at a low operating temperature of 150/spl deg/C is obtained with a fast response time of 14 seconds for 20 ppm of H/sub 2/S 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 SnO/sub 2/ in the presence of H/sub 2/S have been analyzed in the light of space charge regions formed due to distributed p-type CuO islands on the n-type SnO/sub 2/ thin film surface. Dissociated hydrogen available from the CuO-H/sub 2/S interaction spills over and is found to be primarily responsible for the observed fast response characteristics.