Direct Observation of Plasmon Band Formation and Delocalization in Quasi-Infinite Nanoparticle Chains

TL;DR

This study demonstrates the fabrication and detailed analysis of long chains of gold nanoparticles, revealing the formation of a plasmonic band and delocalized modes that enable sub-diffraction light manipulation with low losses.

Contribution

It introduces a scalable self-assembly method for nanoparticle chains and provides a comprehensive understanding of their plasmonic band formation and mode delocalization.

Findings

Plasmonic band forms from coupled nanoparticle modes.

Delocalized modes enable efficient energy transfer over 1500 nm.

Plasmon band confinement allows sub-diffraction light manipulation.

Abstract

Chains of metallic nanoparticles sustain strongly confined surface plasmons with relatively low dielectric losses. To exploit these properties in applications,such as waveguides, the fabrication of long chains of low disorder and a thorough understanding of the plasmon-mode properties, such as dispersion relations, are indispensable. Here, we use a wrinkled template for directed self-assembly to assemble chains of gold nanoparticles. With this up-scalable method, chain lengths from two particles (140 nm) to 20 particles (1500 nm) and beyond can be fabricated. Electron energy-loss spectroscopy supported by boundary element simulations, finite-difference time-domain, and a simplified dipole coupling model reveal the evolution of a band of plasmonic waveguide modes from degenerated single-particle modes in detail. In striking difference from plasmonic rod-like structures, the plasmon band is confined in excitation energy, which allows light manipulations below the diffraction limit. The non-degenerated surface plasmon modes show suppressed radiative losses for efficient energy propagation over a distance of 1500 nm.