Comparison of palladium thin films used in a transmission based optical fibre hydrogen sensor

Abstract

Results are presented of a comparison between two palladium films of different thicknesses used as the sensing element in a transmission based optical fiber hydrogen sensor. The palladium films, 16nm and 26nm thick, were deposited onto glass substrates using thermal vacuum evaporation. The absorption and desorption of hydrogen causes the optical properties of palladium to change depending on the concentration of hydrogen gas it is exposed to. Using a deuterium/halogen light source in conjunction with a UV/VIS spectrometer the changes in the optical transmittance in the visible spectrum of the Pd films was monitored for different concentrations of hydrogen from 0 to 5% in a nitrogen atmosphere. A comparison of the changes in the optical transmission intensity is presented for palladium films as they were exposed to varying concentrations of hydrogen gas. The 26nm palladium film was capable of measuring changes in transmission intensity of up to 46% while the range for the thinner palladium film was 20% when exposed to 5% hydrogen concentration in nitrogen.