# Thermal graphene metamaterials and epsilon-near-zero high temperature plasmonics

## TL;DR

This paper introduces high temperature plasmonic coatings and graphene multilayers that enable spectrally selective thermal emission for thermophotovoltaic applications, utilizing epsilon-near-zero phenomena to enhance near-field heat transfer.

## Contribution

It presents a novel design of single-layer plasmonic coatings and graphene multilayers that achieve spectrally selective thermal emission and near-field energy density enhancement.

## Key findings

- High efficiency spectral tuning of thermal emitters using epsilon-near-zero plasmonics.
- Enhanced near-surface energy density in graphene multilayers at epsilon-near-zero frequencies.
- Potential for large-area, high-temperature thermophotovoltaic applications.

## Abstract

The key feature of a thermophotovoltaic (TPV) emitter is the enhancement of thermal emission corresponding to energies just above the bandgap of the absorbing photovoltaic cell and simultaneous suppression of thermal emission below the bandgap. We show here that a single layer plasmonic coating can perform this task with high efficiency. Our key design principle involves tuning the epsilon-near-zero frequency (plasma frequency) of the metal acting as a thermal emitter to the electronic bandgap of the semiconducting cell. This approach utilizes the change in reflectivity of a metal near its plasma frequency (epsilon-near-zero frequency) to lead to spectrally selective thermal emission and can be adapted to large area coatings using high temperature plasmonic materials. We provide a detailed analysis of the spectral and angular performance of high temperature plasmonic coatings as TPV emitters. We show the potential of such high temperature plasmonic thermal emitter coatings (p-TECs) for narrowband near-field thermal emission. We also show the enhancement of near-surface energy density in graphene-multilayer thermal metamaterials due to a topological transition at an effective epsilon-near-zero frequency. This opens up spectrally selective thermal emission from graphene multilayers in the infrared frequency regime. Our design paves the way for the development of single layer p-TECs and graphene multilayers for spectrally selective radiative heat transfer applications.