Improved durability of Pd/WO3 hydrogen sensor films prepared by sputtering

Double-layer thin films of Pd/WO3 for application in optical hydrogen safety sensors were prepared by sputtering. Raman spectroscopy was used to find the optimal growth condition by comparing with the best-performing thin films prepared by thermal evaporation. Sputtered films show somewhat lower sensitivity to hydrogen gas than evaporation-prepared films, as determined by the maximum change in the optical transmittance. On the other hand, the initial response was faster for the sputtered films. Durability, as measured by monitoring the modulation of the optical transmittance when the films are alternately exposed to hydrogen and air, was much improved for the sputtering-prepared films. The modulation amplitude shows little degradation, even after 500 cycles.