Gold nanorod arrays as plasmonic cavity resonators

Area of Science:

• Plasmonics
• Nanophotonics
• Optical Metamaterials

Background:

• Hexagonal arrays of gold nanorods exhibit discrete plasmon resonance modes.
• These modes are observable at visible and near-infrared wavelengths under normal light incidence.
• The behavior is influenced by nanorod dimensions and the dielectric environment.

Purpose of the Study:

• To investigate the plasmon resonance modes in hexagonal 2D arrays of gold nanorods.
• To understand the influence of nanorod geometry and surrounding medium on these modes.
• To explore the potential for tunable optical properties in such nanorod arrays.

Main Methods:

• Fabrication of hexagonal 2D arrays of gold nanorods on a gold baseplate.
• Characterization of reflectance spectra at visible and near-infrared wavelengths.
• 3D finite-element method (FEM) simulations to model plasmonic behavior.

Main Results:

• Observed multiple resonant attenuations in reflectance spectra, sensitive to nanorod height and dielectric medium.
• Simulations revealed harmonic sets of longitudinal standing waves (quarter-wave modes) in inter-rod cavities, analogous to acoustic resonances.
• Resonance frequencies are tunable by altering nanorod height, diameter-spacing ratio, and host refractive index.
• Strong retardation effects were noted due to coupled transverse modes.
• Predicted resonant transmission through arrays without a baseplate, governed by half-wave modes.

Conclusions:

• Gold nanorod arrays support tunable plasmonic resonances analogous to acoustic waves.
• The observed quarter-wave and predicted half-wave modes offer control over optical properties.
• These findings suggest potential applications in tunable optical devices and metamaterials.