Shape effects on localized surface plasmon resonances in metallic nanoparticles

TL;DR

This paper investigates how smooth shape modifications of metallic nanoparticles influence localized surface plasmon resonances, revealing that small shape changes can significantly alter their optical properties, especially along minimal cross-sections.

Contribution

It introduces a boundary integral equation method to analyze shape effects on nanoparticle plasmon resonances, highlighting the impact of shape variations on eigenvalues and coupling weights.

Findings

Shape changes >12% volume variation alter extinction spectra.

Eigenvalues and coupling weights are most affected along smallest cross-sections.

Small shape modifications can cause large shifts in plasmonic responses.

Abstract

The effect of smooth shape changes of metallic nanoparticles on localized surface plasmon resonances is assessed with a boundary integral equation method. The boundary integral equation method allows compact expressions of nanoparticle polarizability which is expressed as an eigenmode sum of terms that depends on the eigenvalues and eigenfunctions of the integral operator associated to the boundary integral equation method. Shape variations change not only the eigenvalues but also their coupling weights to the electromagnetic field. Thus, rather small changes in the shape may induce large variations of the coupling weights. It has been found that shape changes that bring volume variations >12% induce structural changes in the extinction spectrum of metallic nanoparticles. Also, the largest variations in eigenvalues and their coupling weights are encountered by shape changes along the smallest cross-sections of nanoparticles. These results are useful as guiding rules in the process of designing plasmonic nanostrucrures.