A hydrogen sensor based on thin films Fabry-Perot interferometer using thin film of a-WO3

Thin films of Pd exhibit a change in their optical properties when exposed to hydrogen. A new sensor element consisting of a layered structure metal/dielectric/metal has been developed for optical detection of hydrogen. This sensing structure composed of a combined Pd and a-WO3 thin film stack on Au thin film has been tested. A structure uses a thin a-WO3 film as a resonant cavity and is acting as a Fabry-Perot interferometer. The gasochromic mechanism in amorphous tungsten oxide films has been used. When the Pd/a-WO3 films are gasochromically colored by exposure to diluted hydrogen gas, interference peaks for s- and p-polarized light disappear. Change of optical constants of resonant cavity due to gasochromic coloration in a a-WO3 films is directly related to the double injection of hydrogen ions and electrons. Optical cycling tests confirm that Pd/a-WO3 films can not be bleached without oxygen. The sensor exhibits good sensitivity for low hydrogen concentration and the stability of parameters in room temperature. (author)