Improved response of H/sub 2/S gas sensors with CuO nanoparticles on SnO/sub 2/ film

In our earlier work enhanced H/sub 2/S detection characteristics were observed in a novel sensor structure consisting of uniformly distributed CuO islands on SnO/sub 2/ films. Ultra-thin CuO in the form of dotted islands on SnO/sub 2/ film exhibited a high sensitivity (S = 7.3 /spl times/ 10/sup 3/) at a low operating temperature (150/spl deg/C), and a fast response speed of 14 s was obtained for H/sub 2/S gas detection In the initial study the CuO islands were large in diameter (0.6 mm) quite thick (10 nm) and were widely dispersed (1.2 mm apart). In the present work a systematic study on the catalyst CuO thickness and its distribution is reported and improved response and recovery are shown with chemically derived CuO nanoparticles. The main focus is towards trace-level (20 ppm) H/sub 2/S gas detection and sensor response characteristics including sensitivity and response speed with varying distribution of CuO catalyst on SnO/sub 2/ surface. The sensor operating temperature at which a maximum response is observed is found to decrease to a lower temperature of 130/spl deg/C with surface dispersed CuO nanoparticles. The response speed of the sensors to H/sub 2/S gas becomes progressively faster when the CuO catalyst is dispersed as nanoparticles or as dotted islands onto the SnO/sub 2/ film surface. With the SnO/sub 2/-CuO-nano sensor, a high sensitivity of 2 /spl times/ 10/sup 3/ at a low operating temperature of 130/spl deg/C is obtained with a fast response speed of 16 seconds for 20 ppm of HS gas and a recovery time of 61 seconds is measured. Enhanced catalytic activity is observed due to the presence of CuO nanoparticles and their spatial distribution allows for, an effective removal of adsorbed oxygen from the uncovered SnO/sub 2/ 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.