Visualizing plasmon coupling in closely-spaced chains of Ag nanoparticles by electron energy loss spectroscopy

TL;DR

This study visualized and analyzed plasmon coupling in closely-spaced silver nanoparticle chains using electron energy loss spectroscopy, revealing how coupling modes shift with particle spacing and chain configuration.

Contribution

It provides the first detailed visualization of anisotropic plasmon coupling in nanoparticle chains at nanometer resolution using EELS.

Findings

Redshift of in-phase plasmon mode with decreasing inter-particle distance

Identification of two coupling paths in a 4-particle chain

Confirmation of optical activity through discrete dipole approximation calculations

Abstract

Anisotropic plasmon coupling in closely-spaced chains of Ag nanoparticles was visualized using the electron energy loss spectroscopy in a scanning transmission electron microscope. For dimers as the simplest chain, mapping the plasmon excitations with nanometers' spatial resolution and 0.27 eV energy resolution intuitively identified two coupling plasmons. The in-phase mode redshifted from the ultraviolet region as the inter-particle spacing was reduced, reaching the visible range at 2.7 eV. Calculations based on the discrete dipole approximation confirmed its optical activeness, where the longitudinal direction was constructed as the path for light transportation. Two coupling paths were then observed in an inflexed 4-particle chain.