Substrate matters: Coupled phonon modes of a spherical particle on a substrate probed with EELS

TL;DR

This study uses vib-EELS and numerical modeling to explore how substrate properties influence phonon mode coupling in spherical particles, revealing hybrid modes and the importance of beyond-dipole interactions.

Contribution

It provides new insights into the mechanisms of phonon coupling between particles and substrates, emphasizing the role of dielectric composition and hybridization effects.

Findings

Hybrid phonon modes depend on substrate dielectric properties.

Mirror charge effects dominate in dielectric films.

Phonon mode hybridization occurs in metallic films.

Abstract

Using vibrational electron energy loss spectroscopy (vib-EELS) combined with numerical modeling, we investigate the physical mechanisms governing the phonon coupling between a spherical particle sustaining multipolar surface phonon modes and an underlying thin film. Depending upon their dielectric composition, a variety of hybrid phonon modes arise in the EEL spectrum due to the interaction between polarization charges in the particle and film. Mirror charge effects and phonon mode hybridization are the active mechanisms acting on dielectric and metallic-type films, respectively. Processes beyond dipole-dipole interactions are required to describe the sphere-film coupling.