Sensitive Hydrogen Sensors Based on Gold–Palladium Double Nanoblock

We suggest a new plasmonic hydrogen sensor based on a metal–air–metal cavity structure. The proposed cavity structure shows a high sensing performance with a large resonant wavelength shift of 84 nm due to strong plasmonic coupling at an air gap size of 8 nm. The cavity resonance has a narrow linewidth of 72 nm by suppressing radiational loss. Figure of merit, defined by the ratio between the wavelength shift and linewidth, is estimated to be 1.17, which means that the cavity can detect hydrogen gas effectively. In addition, optical losses in the plasmonic cavity, radiational loss, and metallic absorption losses are separately investigated as a function of air gap size.