Mechanism of drifts in H2S sensing properties of SnO2:CuO composite thin film sensors prepared by thermal evaporation

Hydrogen sulphide (H2S) sensors, exhibiting high sensitivity (>10(4) in 50 ppm of H2S) and short response time (80 s), have been developed employing tin oxide:copper oxide (SnO2:CuO) composite thin films. The films were prepared by thermal evaporation of Sn and Cu metals on recrystallized alumina substrates, followed by oxidation at high temperatures. Results of various studies, such as, scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) reveal that SnO2 and CuO are mutually non-reactive. The CuO grains, which in turn reside in the inter-granular regions of SnO2, inhibit grain growth of SnO as well as form a network of p-n junctions. Results of XPS measurements revealed that the formation of Cu(OH)(2) due interaction of sensor film with ambient moisture causes drifts in sensor characteristics (low sensitivity and slow response) on prolonged operation in the industrial environment. The sensitivity and response time of degraded sensors could be restored either by exposing the sensor to a high H2S dose (>100 ppm) or by heating it to an elevated temperature (>400 degreesC). (C) 2003 Elsevier B.V. All rights reserved.