Linear optical properties of a linear chain of interacting gold nanoparticles

TL;DR

This study models the optical properties of a chain of gold nanoparticles, revealing how dipole interactions affect surface plasmon resonance and permittivity depending on light polarization, size, and medium.

Contribution

It provides an analytical expression for nanoparticle permittivity considering dipole interactions in a chain, with numerical analysis for different sizes and media.

Findings

Parallel polarization increases extinction cross section and causes red-shift in SPR.

Perpendicular polarization decreases extinction cross section and causes blue-shift in SPR.

Edge particles show less variation in optical properties than central particles.

Abstract

In a Drude-like model for the conduction electrons of Metal Nanoparticles (MNPs) in a periodic linear chain, considering dipole-dipole interactions of adjacent particles, an analytical expression is derived for each particle permittivity for two different polarizations of incident light: parallel with and perpendicular to the chain line. A numerical analysis is carried out for a chain including 10 identical gold Nanoparticles (NPs) for two different sizes of NPs and two different host media of air and glass. It is shown that in the parallel case of polarization, interaction of NPs leads to a substantial increase in the extinction cross section and the red-shift of the Surface Plasmon Resonance (SPR) wavelength. In comparison with the linear properties of a single NP, the second and penultimate particles have the most increase in the extinction cross section and SPR wavelength displacement while the first and last particles experience the least variations due to the mutual interactions. For the perpendicular polarization, inversely, the dipolar coupling causes the decrease in extinction cross section of all particles and the blue-shift of SPR wavelength. For the parallel polarization, the absolute values of the real and imaginary parts of complex permittivity of each MNP decrease in comparison with the single particle case while they increase for the perpendicular state of polarization.