Gas sensing with films of nanocrystalline WO3 and Pd made by advanced reactive gas deposition

Films consisting of nanocrystalline WO3 and Pd, produced by advanced reactive gas deposition, were investigated for gas sensing applications. X-ray diffractometry and electron microscopy showed that as-deposited WO3 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 H2S 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 H2S and that the devices exhibited extreme room-temperature sensitivities, of up to ∼5000 for 10 ppm for H2S. An unambiguous response, with a sensitivity of ∼10, was observed for as little as 0.5 ppm of H2S. 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.