Nanomaterials for environmental applications:: novel WO3-based gas sensors made by advanced gas deposition

Nanocrystalline WO3 films were prepared by gas evaporation and deposition. Their gas-sensing properties were investigated in two types of devices. Firstly, the films were exposed to a set of probing gases while the mean conductance change was recorded at various gas concentrations and temperatures. For example, 5 ppm of H2S yielded a conductance increase by similar to250 times even at room temperature, and doping by Al or Au enhanced the sensitivity still further. The maximum sensitivity for H2S, N2O, and CO was found at 400, 525, and 700 K, respectively. For another sensor arrangement, conduction noise was measured in the 0.5-45 Hz frequency range for thin Au films covered with WO3 nanoparticles. The power density of the conductance fluctuations was increased by about two orders of magnitude after alcohol exposure, while the mean resistance changed by less than 0.3%, thus showing the potential of fluctuation-based gas sensing. (C) 2004 Elsevier B.V. All rights reserved.