Ultraconfined Plasmons in Atomically Thin Crystalline Silver Nanostructures

Abstract

The ability to confine light down to atomic scales is critical for the development of applications in optoelectronics and optical sensing as well as for the exploration of nanoscale quantum phenomena. Plasmons in metallic nanostructures with just a few atomic layers in thickness can achieve this type of confinement, although fabrication imperfections down to the subnanometer scale hinder actual developments. Here, we demonstrate narrow plasmons in atomically thin crystalline silver nanostructures fabricated by prepatterning silicon substrates and epitaxially depositing silver films of just a few atomic layers in thickness. Specifically, we lithographically pattern a silicon wafer to introduce on‐demand lateral shapes, chemically process the sample to obtain an atomically flat silicon surface, and epitaxially deposit silver to obtain ultrathin crystalline metal films with the designated morphologies. Structures fabricated by following this procedure allow for an unprecedented control over optical field confinement in the near‐infrared spectral region, which is here illustrated by the observation of fundamental and higher‐order plasmons featuring extreme spatial confinement and high‐quality factors that reflect the crystallinity of the metal. We report a substantial improvement in the degree of spatial confinement and quality factor that should facilitate the design and exploitation of atomic‐scale nanoplasmonic devices for optoelectronics, sensing, and quantum‐physics applications.This article is protected by copyright. All rights reserved

Toward Optimum Coupling between Free Electrons and Confined Optical Modes

“…Two-dimensional (2D) materials have become a relevant ingredient in nanophotonics because of their robustness, flexible integration, large tunability through electrical gating, and extraordinary optical properties that include a plethora of long-lived polaritons in van der Waals materials such as plasmons in graphene, − phonon-polaritons in hexagonal boron nitride (hBN) and α-MoO 3 , , and excitons in transition-metal dichalcogenides (TMDs), as well as plasmons in atomically thin noble-metal nanostructures. , The scaling properties of 2D nanostructures are different from those of 3D particles, as one is interested in maintaining a constant thickness d while varying the lateral size D . In addition, the mode frequencies of atomically thin structures are generally small, so they can be described in the quasistatic limit.…”