Crystalline metal flakes: Platforms for advanced plasmonics and hybrid 2D material architectures

TL;DR

Crystalline noble metal flakes offer atomically flat, high-quality surfaces that enhance nanophotonic applications like plasmonics, quantum light generation, and hybrid 2D material systems, surpassing traditional polycrystalline films.

Contribution

This review highlights the unique advantages of crystalline metal flakes in nanophotonics, emphasizing their role in advancing plasmonics, quantum optics, and hybrid architectures.

Findings

Crystalline flakes enable low-loss plasmonic and quantum optical phenomena.

They serve as precise templates for nanostructuring with minimal surface roughness.

Flakes support 2D plasmons and function as near-ideal mirrors at infrared wavelengths.

Abstract

Crystalline noble metal flakes are emerging as versatile platforms in nanophotonics, enabling a broad range of optical phenomena and applications. Their atomically flat surfaces, high crystallinity, and superior optical quality open new avenues in advanced plasmonics, quantum light generation, and hybrid photonic systems. In contrast to conventional polycrystalline metal films, which typically suffer from higher optical losses due to grain boundaries, surface roughness, and structural disorder, these monocrystalline flakes provide minimal scattering and enhanced performance. They serve as templates for precise nanostructuring through techniques like focused-ion beam (FIB) milling and are crucial for advanced applications in sensing and optoelectronics. Additionally, they facilitate frontier research in quantum plasmonics, enabling fundamental studies of nonlocal optical effects and the generation of nonclassical light. Furthermore, the well-defined $\{111\}$ facets of these flakes host Tamm--Shockley surface states that support 2D plasmons coexisting with bulk modes. At near-infrared wavelengths and beyond, crystalline flakes act as nearly ideal metallic mirrors, featuring surface roughness limited only to atomic terrace steps, making them highly suitable for integration with 2D materials in hybrid photonic architectures. This review surveys the key roles these flakes play, highlighting recent developments and discussing future prospects while emphasizing their unique benefits in addressing fundamental and applied challenges in modern nanophotonics.