Ultra-sensitive hydrogen detector based on palladium-gold hole array

We investigate a hydrogen sensor based on palladium (Pd) in a plasmonic structure. A layer of Pd is deposed on a gold substrate and an elliptical hole array is on the Pd-Au structure. The Pd will transform to Pd-Hx in a hydrogen-rich gas environment, and the dielectric constants of Pd-Hx will change with the concentration of hydrogen. To ensure safety, the concentration of H2 in air must be below 4%. We calculate the absorption spectra (ΔA) of the sensor by Finite-difference time-domain method (FDTD). The results show that the difference between absorptions in air of H2-less (0%) and H2-rich (4%) environment ΔA can reach to 0.136. The major influence factor is the size of the hole. We also discuss influence of the period of the array. With a small period less than the incident wavelength, the maximum value of ΔA linearly decreases with the increase of the period. This shows that there is a strong interaction among the units. For a large period, the long-range interaction will appear, which is tuned by the period and the incident wavelength. The long-range interaction may have a little effect on the maximum value of ΔA. Our proposed structure shows an excellent ability to sense H2.