Collective resonances in plasmonic crystals: Size matters

TL;DR

This study investigates how the size of metallic nanoparticle arrays influences Surface Lattice Resonances, revealing size-dependent effects on resonance quality factors and providing insights into collective plasmonic behavior.

Contribution

The paper demonstrates the size-dependent evolution of Surface Lattice Resonances in nanoparticle arrays using experimental and theoretical methods, highlighting finite size effects on optical properties.

Findings

SLRs' Q-factors increase with array size.

Arrays smaller than 5x5 have lower SLR Q-factors than LSPRs.

Arrays larger than 20x20 have saturated, higher SLR Q-factors.

Abstract

Periodic arrays of metallic nanoparticles may sustain Surface Lattice Resonances (SLRs), which are collective resonances associated with the diffractive coupling of Localized Surface Plasmon Resonances (LSPRs). By investigating a series of arrays with varying number of particles, we traced the evolution of SLRs to its origins. Polarization resolved extinction spectra of arrays formed by a few nanoparticles were measured, and found to be in very good agreement with calculations based on a coupled dipole model. Finite size effects on the optical properties of the arrays are observed, and our results provide insight into the characteristic length scales for collective plasmonic effects: for arrays smaller than 5 x 5 particles, the Q-factors of SLRs are lower than those of LSPRs; for arrays larger than 20 x 20 particles, the Q-factors of SLRs saturate at a much larger value than those of LSPRs; in between, the Q-factors of SLRs are an increasing function of the number of particles in the array.