Multipolar Nanocube Plasmon Mode-Mixing in Finite Substrates

Area of Science:

• Plasmonics and Nanophotonics
• Materials Science
• Surface Science

Background:

• Controlling radiative and nonradiative properties of plasmonic nanostructures is crucial for applications in biology, chemistry, optics, information, and energy.
• Tuning plasmon spectrum, light/heat coupling, quality factor, and optical mode volume is essential for nanophotonic devices and molecular sensors.
• Existing methods for tuning plasmonic properties are diverse, but simple experimental approaches are highly sought after.

Purpose of the Study:

• To investigate the underappreciated effects of substrate thickness and dielectric composition on plasmon hybridization.
• To demonstrate how substrate properties can nontrivially mix free-space plasmon modes.
• To elucidate the impact of substrate-induced plasmon mixing on the plasmonic density of states and optical properties.

Main Methods:

• Experimental investigation using electron energy-loss spectroscopy (EELS).
• Numerical simulations to model plasmon behavior.
• Analytical modeling to understand the underlying physics of plasmon hybridization.

Main Results:

• Substrate thickness, even as low as ∼10 nm, significantly influences plasmon hybridization.
• Mixing of dark and bright plasmon modes occurs due to finite substrates, altering optical properties.
• Substrate effects were observed in the mixing of dipole, quadrupole, and octupole corner-localized plasmon resonances in silver nanocubes.

Conclusions:

• Substrate properties offer a facile route to tune the optical characteristics of plasmonic nanostructures.
• Finite substrate effects provide a powerful tool for manipulating plasmonic density of states and near/far-field responses.
• This understanding can lead to improved performance in nanophotonic devices and sensors.