Optimizing Refractive Index Sensitivity of Supported Silver Nanocube Monolayers

Abstract

The refractive index (RI) sensitivity of extinction spectra was compared experimentally for silver nanocubes in solution and in supported monolayers prepared by the Langmuir technique. The size of the nanocubes, RI of supporting dielectric substrate, and monolayer surface pressure were used as variables in refractive index sensing optimization. The dipolar plasmon modes of the colloidal nanocubes were found to have the highest RIS values of 176, 361, and 480 nm/RI units for 40, 80, and 130 nm cubes, respectively. The largest figure of merit (FOM) of 4.55 was measured for a quadrupolar mode of 130 nm nanocubes. When compared to suspensions, the refractive index sensitivities (RIS) of supported nanocubes were reduced by ∼50% and decreased with increasing monolayer surface pressure. The RIS of 40 nm cube monolayers appeared to be sensitive to the substrate RI due to the RI-dependent plasmon mode hybridization, resulting in dipolar and quadrupolar modes. The intensity of this quadrupolar peak was found to inc...