PREPARATION AND CHARACTERIZATION OF AN OPTICALLY DETECTABLE H-2 GAS SENSOR CONSISTING OF PD/MOO3 THIN-FILMS

Double-layered thin films consisting of a sputtered MoO3 layer covered with a very thin Pd layer are prepared on a glass substrate, and their colouration behaviour under an H-2 atmosphere is examined in detail. The transmittance of the film at 780 nm is decreased from 50% to almost 0% by exposing the film to Ar gas containing 0.1 vol.% H-2 for only 100 s. The colouration rate is significantly affected by the H-2 concentration; it increases with an increase in H-2 concentration. From an observation of isolated Mo5+ species in the ESR spectrum of the coloured film, the colouration may originate from the formation of Mo5+ under an H-2 atmosphere. Colouration is not observed after exposing the film to methane and/or isobutane gas, which assures the high selectivity for H-2 gas sensing of the present sensor.