Optically Thin Metallic Films for High-radiative-efficiency Plasmonics

TL;DR

This paper proposes and theoretically studies optically thin metallic films as a high-efficiency plasmonic platform, combining the advantages of nanoparticles and metallic films to achieve high radiative efficiency and strong light-matter interactions.

Contribution

It introduces the concept of optically thin metallic films for plasmonics, demonstrating their potential for high-radiative-efficiency and near-field enhancement through theoretical analysis.

Findings

High Purcell factor (>10^4) for spontaneous emission.

Quantum yield exceeds 50% even at small gaps.

Enhanced far-field scattering with high quality factor.

Abstract

Plasmonics enables deep-subwavelength concentration of light and has become important for fundamental studies as well as real-life applications. Two major existing platforms of plasmonics are metallic nanoparticles and metallic films. Metallic nanoparticles allow efficient coupling to far field radiation, yet their synthesis typically leads to poor material quality. Metallic films offer substantially higher quality materials, but their coupling to radiation is typically jeopardized due to the large momentum mismatch with free space. Here, we propose and theoretically investigate optically thin metallic films as an ideal platform for high-radiative-efficiency plasmonics. For far-field scattering, adding a thin high-quality metallic substrate enables a higher quality factor while maintaining the localization and tunability that the nanoparticle provides. For near-field spontaneous emission, a thin metallic substrate, of high quality or not, greatly improves the field overlap between the emitter environment and propagating surface plasmons, enabling high-Purcell (total enhancement > $10^4$), high-quantum-yield (> 50 %) spontaneous emission, even as the gap size vanishes (3$\sim$5 nm). The enhancement has almost spatially independent efficiency and does not suffer from quenching effects that commonly exist in previous structures.