Optical fiber hydrogen sensor based on an annealing-stimulated Pd–Y thin film

Pd–Y alloy has been widely studied for hydrogen separation because of its higher permeability to H than other Pd-based alloys, but the aging behavior in air atmosphere limits its application in fast hydrogen detection. An optical fiber bundle sensor was proposed here to determine the reflective response characteristics of an annealing-restored Pd–Y film. The 30-nm-thick Pd0.92–Y0.08 alloy film was deposited on a fused quartz substrate by co-sputtering and then placed in air aging condition at 20 °C for 1 month. After 200 °C thermal annealing, the response/recovery rate and signal value were monitored in hydrogen concentration ranging from 0.1% to 2% by the optical sensor system, while the microstructure of the film was characterized via atomic force microscopy and X-ray diffraction. The experimental results show that the response properties and crystallinity of the alloy film have achieved a great enhancement after the thermal annealing process, which suggests that H absorption and sensitivity of the film are restored. Attributing to the stress relaxation mechanism, a less than 5% zero drift is achieved under cyclic absorption/desorption of hydrogen. Compared to our previous work, the reflective value represented an approximately linear relationship to the hydrogen concentration. The stability and sensitivity of this annealing-restored film demonstrate the promising of Pd–Y alloy to fabricate economical and sensitive sensor for long term optical detection of hydrogen in low concentration.