Highly tunable infrared extinction properties of gold nanocrescents

The infrared extinction properties of gold nanocrescents fabricated using nanosphere template lithography were studied. The nanocrescents exhibit multiple, structurally tunable localized surface plasmon resonances (LSPRs) across a broad spectral range (560-3600 nm). Plasmon resonances in the infrared have large extinction efficiencies of similar to 20 and peaks as narrow as 0.07 eV. The nanocrescents also have high refractive index sensitivities (370-880 nm/RIU) that are proportional to the LSPR wavelengths. The sensing figure of merit measured for ensembles of nanocrescents is as high as 2.4 for near-infrared plasmon resonances.