Effect of Nanogap Morphology on Plasmon Coupling

Area of Science:

• Plasmonics
• Nanophotonics
• Surface Chemistry

Background:

• Plasmon coupling in nanoparticle assemblies is key for tuning optical resonances.
• Resonance energies depend on nanogap parameters, with studies often focusing on distance.
• The effect of nanogap morphology on plasmon coupling remains less explored.

Purpose of the Study:

• To investigate the influence of nanogap morphology on plasmon coupling in nanoparticle dimers.
• To compare the effect of different gap shapes (face, edge, vertex) between gold nanospheres and nanocubes.

Main Methods:

• Fabrication of gold nanoparticle dimers with varying nanogap morphologies using gold nanospheres (AuNSs) and gold nanocubes (AuNCs).
• Characterization using dark-field single-particle scattering spectroscopy.
• Computational analysis using simulations to understand charge density and Coulomb interactions.

Main Results:

• The longitudinal plasmon coupling mode shifts to lower energies as the nanogap morphology transitions to higher curvature regions (edge, vertex) of the AuNC.
• Simulations confirm that higher charge density at the vertex or edge of the AuNC contributes to lower plasmon coupling energy via Coulomb interaction.
• Differences in plasmon energies and polarizability across the AuNC faces, edges, and vertices alone do not significantly shift the plasmon coupling mode.

Conclusions:

• Nanogap morphology, specifically curvature, plays a crucial role in tuning plasmon coupling, independent of gap distance.
• Coulomb interactions, influenced by charge density variations at different AuNC surface features, are the primary drivers for the observed shifts in plasmon coupling energy.
• This work highlights the importance of considering gap geometry for precise control over optical properties in nanoparticle assemblies.