High figure of merit hydrogen sensor using multipolar plasmon resonance modes

Fabrication of long Au nanorods (AuNRs) has resulted in the appearance of higher order plasmon resonance modes, or multipoles, in the absorbance spectrum that can be monitored as a function of time and gas exposure. Due to the proximity of the multipolar mode to the transverse dipole mode of the AuNRs, both modes were monitored as the sample was exposed to hydrogen in an air background. These results were also compared to a shorter AuNR sample where the longitudinal dipole peak position matched the multipolar peak position. Polarization dependence of the higher order resonance as well as boundary element method (BEM) simulations confirm that the mode order is n = 3. Due to the 36% decrease in linewidth of the multipolar peak compared to the dipole, the figure of merit (FoM) of the multipolar resonance is calculated to be 22% higher than the longitudinal dipole resonance for the shown gas sensing results and is promising for high temperature gas sensing applications.