dc and ac characterizations of WO3 sensors under ethanol vapors

This work deals with mechanisms of ethanol detection by WO3 sensors. In the devices considered, the sensitive layer, deposited by reactive RF magnetron sputtering, is thin (50 nm) and polycrystalline. Although metal oxide semiconductor materials (such as SnO2 or WO3) were successfully used as sensitive layer for organic vapor sensors, the proposed detection mechanisms are generally deduced from the dc responses only. Here, ac impedance spectroscopy is coupled with dc measurements to determine the regions of the sensor device (electrodes, grains or grain boundaries), which are crucial for the detection of ethanol. Results show that ethanol is oxidized mainly on the surface of the WO3 grains, which implies the presence on the surface of a pre-adsorbed O− species.