Comparisons of Surface Plasmon Sensitivities in Periodic Gold Nanostructures

The wavelength sensitivities of three kinds of nanostructures (nanoslits, nanoholes, and concentric circles) with various aperture sizes were compared in water environment. These nanostructures were made on a 110-nm-thick gold film with a period of 600 nm. Surface plasmon resonances in these nanostructures produce transmission dips near the phase-matching conditions while peaks at longer wavelengths. The wavelength sensitivities measured at dips are close to theoretical predictions and about 1.5 times larger than those measured at peaks. Such sensitivity difference is attributed to various surface plasmon distributions, as illustrated by the finite-difference time-domain calculations. In addition, the sensitivity decreases with the increase of aperture size. The nanoslit array and concentric circles have better sensitivities than the nanohole array due to the no cut-off transmission.