Analysis of hydrogen exposure effects on the transmittance of periodic sub-wavelength palladium hole arrays

In a previous study, we have reported transmittance variations of sub-wavelength palladium hole arrays upon exposure to hydrogen. The main resonance peak of the microfabricated palladium hole arrays exhibiting the extraordinary transmission effect decreases when exposed to the lower flammability concentration of hydrogen in air. This variation in transmittance was attributed to a combination of two effects, namely, a change in the dimension of the array holes due to the expansion of palladium upon hydrogen absorption, and/or a change in the permittivity of the palladium layer upon formation of the palladium hydride phase. In this study, we examine the relative strength of the two effects by finite-difference-time-domain simulation. Our simulation results show that the transmittance variation upon exposure to hydrogen is predominantly caused by the lateral expansion of the palladium layer, which induced a decrease in the hole width of the array.