Gas sensing with films of nanocrystalline WO 3 and Pd made by advanced reactive gas deposition

Abstract

Films consisting of nanocrystalline WO 3 and Pd, produced by advanced reactive gas deposition, were investigated for gas sensing applications. X-ray diffractometry and electron microscopy showed that as-deposited WO 3 and Pd had tetragonal and cubic structures, respectively, both with an average grain size of ∼5 nm. The films had Pd/W atomic ratios of 0, 0.5 and 13% and were sintered at temperatures up to 873 K. Gas sensing properties of the films, manifested in relative conductivity changes, were studied for exposure to H 2S and CHOH at operation temperatures up to 773 K. It was found that the addition of Pd decreased the recovery time of the sensor, furthermore increased the low-concentration sensitivity for H 2S and that the devices exhibited extreme room-temperature sensitivities, of up to ∼5000 for 10 ppm for H 2S. An unambiguous response, with a sensitivity of ∼10, was observed for as little as 0.5 ppm of H 2S. The sensors were also able to detect 45 ppm of CHOH. In addition it is shown that Pd doping widens the number of detectable gases.