Real-space imaging of acoustic plasmons in large-area CVD graphene

TL;DR

This study visualizes and characterizes acoustic plasmons in large-area CVD graphene, revealing their confinement, damping properties, and potential for mid-IR optoelectronic applications.

Contribution

It provides the first real-space imaging of acoustic plasmons in large-area graphene, demonstrating their low damping and strong confinement at ambient conditions.

Findings

Acoustic plasmons exhibit high confinement and low damping in large-area graphene.

Real-space imaging of acoustic plasmons is achieved using near-field scattering microscopy.

Resonant acoustic Bloch states are observed in gold nanoribbon arrays, enhancing far-field coupling.

Abstract

An acoustic plasmonic mode in a graphene-dielectric-metal heterostructure has recently been spotlighted as a superior platform for strong light-matter interaction. It originates from the coupling of graphene plasmon with its mirror image and exhibits the largest field confinement in the limit of a nm-thick dielectric. Although recently detected in the far-field regime, optical near-fields of this mode are yet to be observed and characterized. Direct optical probing of the plasmonic fields reflected by the edges of graphene via near-field scattering microscope reveals a relatively small damping rate of the mid-IR acoustic plasmons in our devices, which allows for their real-space mapping even with unprotected, chemically grown, large-area graphene at ambient conditions. We show an acoustic mode that is twice as confined - yet 1.4 times less damped - compared to the graphene surface plasmon under similar conditions. We also image the resonant acoustic Bloch state in a 1D array of gold nanoribbons responsible for the high efficiency of the far-field coupling. Our results highlight the importance of acoustic plasmons as an exceptionally promising platform for large-area graphene-based optoelectronic devices operating in mid-IR.