[Paper Review] Non-radiative and radiative decays in nanogap emitting devices

Rémi Faggiani, Jianji Yang+1 more|arXiv (Cornell University)|Oct 22, 2015

Plasmonic and Surface Plasmon Research6 references3 citations

TL;DR

This paper provides closed-form expressions for quenching and gap plasmon decay rates in nanogap emitters, enabling a systematic design of plasmonic nanoantennas. It shows that emission rates can exceed quenching losses in specific material combinations, regardless of gap size, offering a general framework for optimizing emission acceleration and extraction efficiency.

ABSTRACT

By placing a quantum emitter in the mouths of nanogaps consisting of two metal nanoparticles nearly into contact, significant increases in emission rate are obtained. This mechanism is central in the design of modern plasmonic nanoantennas. However, due to the lack of general knowledge on the balance between the different decay rates in nanogaps (emission, quenching, and metal absorption), nanoantenna design is performed in a rather haphazard fashion and relies on repeated numerical calculations; general intuitive design recipes do not presently exist. With accurate and simple closed-form expressions for the quenching rate and the decay rate into gap plasmons, we provide a comprehensive analysis of nanogap light emitting devices in the limit of small gap thickness. We disclose that the total spontaneous emission rate of quantum emitters in nanometer-thin gaps can largely overcome quenching, for specifically selected metallic and insulator materials, regardless of the gap size. Furthermore, to help further designs, we propose a classification of nanogap emitting devices based on two important figures of merit, the emission rate acceleration and the extraction efficiency, and further position a whole family of state-of-the-art devices based on nanogaps formed by nanocubes laying on metallic substrates in the classification.

Motivation & Objective

• To address the lack of general design principles for nanogap emitting devices due to insufficient understanding of decay rate balances.
• To derive accurate, closed-form expressions for quenching rate and decay rate into gap plasmons in ultrathin nanogaps.
• To establish a classification of nanogap devices based on emission rate acceleration and extraction efficiency as key figures of merit.
• To identify material combinations where spontaneous emission rates surpass quenching, enabling efficient light emission independent of gap thickness.

Proposed method

• Derivation of closed-form analytical expressions for the quenching rate and the decay rate into gap plasmons in the limit of small gap thickness.
• Use of electromagnetic theory to model the interaction between a quantum emitter and a nanogap formed by two metal nanoparticles.
• Incorporation of material-dependent dielectric functions for metals and dielectrics to assess the impact of material choice on decay rates.
• Definition and calculation of two key figures of merit: emission rate acceleration and extraction efficiency, to classify device performance.
• Application of the derived expressions to analyze a family of state-of-the-art devices based on nanocubes on metallic substrates.
• Systematic comparison of emission dynamics across different material combinations to identify optimal configurations.

Experimental results

Research questions

• RQ1 Can closed-form expressions accurately describe the quenching and gap plasmon decay rates in nanogap emitters with sub-nanometer gaps?
• RQ2 Under what material conditions can the total spontaneous emission rate exceed quenching losses in nanogap devices?
• RQ3 How do emission rate acceleration and extraction efficiency vary across different nanogap geometries and materials?
• RQ4 What general design principles can be derived from the balance of radiative and non-radiative decay pathways in nanogaps?

Key findings

• Closed-form expressions for quenching and gap plasmon decay rates are derived, enabling analytical prediction of emission dynamics in nanogaps.
• For specific combinations of metallic and insulator materials, the total spontaneous emission rate in nanogap devices can exceed quenching losses regardless of gap thickness.
• The emission rate acceleration and extraction efficiency are identified as critical figures of merit for classifying and optimizing nanogap emitter performance.
• A family of state-of-the-art devices based on nanocubes on metallic substrates is positioned within the proposed classification framework based on their emission and efficiency characteristics.
• The results demonstrate that material selection plays a decisive role in overcoming non-radiative losses, enabling efficient light emission from nanogap emitters.