Observation of a surface lattice resonance in a fractal arrangement of gold nanoparticles

TL;DR

This study demonstrates that a Sierpinski fractal arrangement of gold nanoparticles exhibits a collective surface lattice resonance, similar to periodic structures, with potential for enhanced plasmonic sensing applications.

Contribution

It is the first to experimentally observe surface lattice resonances in a fractal nanoparticle arrangement, supported by numerical simulations.

Findings

Observation of a Fano-like scattering feature

Efficient excitation of collective resonance via Fourier components

Numerical validation with coupled-dipole and FDTD simulations

Abstract

The collective response of closely spaced metal particles in non-periodic arrangements has the potential to provide a beneficial angular and frequency dependence in sensing applications. In this paper, we investigate the optical response of a Sierpinski fractal arrangement of gold nanoparticles and show that it supports a collective resonance similar to the surface lattice resonances that exist in periodic arrangements of plasmonic resonators. Using back focal plane microscopy, we observe the leakage of radiation out of a surface lattice resonance that is efficiently excited when the wavenumber of the incident light matches a strong Fourier component of the fractal structure. The efficient coupling between localized surface plasmons leads to a collective resonance and a Fano-like feature in the scattering spectrum. Our experimental observations are supported by numerical simulations based on the coupled-dipole approximation and finite-difference time-domain methods. This work presents a first step towards the application of fractal arrangements for plasmonic applications