Thermal radiation control from hot graphene electrons coupled to a photonic crystal nanocavity

Cheng Tan,Dirk Englund,Ren-Jye Shiue,Dmitri K. Efetov,Yuanda Gao,Jiabao Zheng,Cheng Peng,Young Duck Kim,James Hone

doi:10.1038/s41467-018-08047-3

Abstract

Controlling thermal radiation is central in a range of applications including sensing, energy harvesting, and lighting. The thermal emission spectrum can be strongly modified through the electromagnetic local density of states (EM LDOS) in nanoscale-patterned metals and semiconductors. However, these materials become unstable at high temperature, preventing improvements in radiative efficiency and applications such as thermophotovoltaics. Here, we report stable high-temperature thermal emission based on hot electrons (>2000 K) in graphene coupled to a photonic crystal nanocavity, which strongly modifies the EM LDOS. The electron bath in graphene is highly decoupled from lattice phonons, allowing a comparatively cool temperature (700 K) of the photonic crystal nanocavity. This thermal decoupling of hot electrons from the LDOS-engineered substrate opens a broad design space for thermal emission control that would be challenging or impossible with heated nanoscale-patterned metals or semiconductor materials.

Highlights

Controlling thermal radiation is central in a range of applications including sensing, energy harvesting, and lighting
This approach has two key advantages: (i) the thermal emission that arises from the graphene electron gas, whose temperature is highly decoupled from graphene’s atomic lattice, can exceed 2000 K, while the surrounding Si cavity itself stays at only 700 K. (ii) The planar photonic crystal (PPC) cavity strongly modifies the LDOS, producing a sharp redistribution of the hot electrons’ thermal emission into the desired spectral regions
This chip-integrated, spectrally controlled black-body radiator can serve as a useful light source for optical communications with low-power requirements

Summary

Introduction

Controlling thermal radiation is central in a range of applications including sensing, energy harvesting, and lighting. The electron bath in graphene is highly decoupled from lattice phonons, allowing a comparatively cool temperature (700 K) of the photonic crystal nanocavity This thermal decoupling of hot electrons from the LDOS-engineered substrate opens a broad design space for thermal emission control that would be challenging or impossible with heated nanoscale-patterned metals or semiconductor materials. A variety of structures have been developed to tailor thermal radiation in this way, including optical gratings[5], photonic crystals[1,6,7], photonic cavities[8,9], nanoantenna[10], and metamaterials[11,12,13] These demonstrations highlight the control of thermal emission by control of the LDOS, but face challenges in high-temperature stability as melting, evaporation, chemical reactions, surface diffusion, and delamination become severe for these nanoscale-patterned metallic and semiconducting materials. This approach has two key advantages: (i) the thermal emission that arises from the graphene electron gas, whose temperature is highly decoupled from graphene’s atomic lattice, can exceed 2000 K, while the surrounding Si cavity itself stays at only 700 K. (ii) The PPC cavity strongly modifies the LDOS, producing a sharp redistribution of the hot electrons’ thermal emission into the desired spectral regions

Methods

Results

Conclusion