Geometry Dependent Localization of Surface Plasmons on Random Gold Nanoparticle Assemblies

TL;DR

This study investigates how the localization of surface plasmons in disordered gold nanoparticle assemblies depends on particle thickness, revealing a transition in localization behavior driven by nanoparticle polarizability.

Contribution

It demonstrates the thickness-dependent localization behavior of surface plasmons in disordered gold nanoparticle assemblies using combined experimental and numerical methods.

Findings

Localization increases with higher mode energies for flat NPs (<0.4 nm)

Localization decreases with higher mode energies for thick NPs (>10 nm)

A transition mode energy with minimal localization exists in intermediate thicknesses

Abstract

Assemblies of plasmonic nanoparticles (NPs) support hybridized modes of localized surface plasmons (LSPs), which delocalize in geometrically well-ordered arrangements. Here, the hybridization behavior of LSPs in geometrically completely disordered arrangements of Au NPs fabricated by an e-beam synthesis method is studied. Employing electron energy loss spectroscopy in a scanning transmission electron microscope in combination with numerical simulations, the disorder-driven spatial and spectral localization of the coupled LSP modes that depend on the NP thickness is revealed. Below 0.4 nm sample thickness (flat NPs), localization increases towards higher hybridized LSP mode energies. In comparison, above 10 nm thickness, a decrease of localization (an increase of delocalization) with higher mode energies is observed. In the intermediate thickness regime, a transition of the energy dependence of the localization between the two limiting cases, exhibiting a transition mode energy with minimal localization, is observed. This behavior is mainly driven by the energy and thickness dependence of the polarizability of the individual NPs.