Effects of Coherent Interactions on the Sensing Characteristics of Near-Infrared Gold Nanorings

We have investigated the surface-supported 2D periodic array of gold nanorings and found that the sensing figure of merit can be significantly improved by coherent interactions. The experiments on the periodic nanostructures fabricated on glass substrate have shown that the sensing characteristics depend on the lattice constant and the character of the substrate grating order at a grazing angle. In the evanescent grating order range, as the lattice constant increases, the plasmon peak red-shifts, line shape strongly narrows and sensitivity decreases, but the figure of merit increases. The reason for the decrease in sensitivity is found to be the decreased field confinement and enhanced substrate effects caused by the coherent interactions. In the radiative grating order range, as the lattice constant increases, the plasmon peak blue-shifts, the line shape significantly broadens and the figure of merit decreases. The experimental results were confirmed by numerical calculations using 3D finite difference time domain method. The simulation results predict that, compared to the single nanoparticle, the bulk sensing figure of merit of the periodic array can be improved by more than three times and the surface sensing figure of merit can be improved by around 2.5 times. The grating-induced modes related to the substrate grating order found only in simulations are also discussed and show strongly suppressed sensitivity and low figure of merit.