Electroluminescence in mid-IR of hBN-encapsulated graphene under large bias was recently put into evidence through spectroscopy and noise thermometry. We demonstrate in this presentation that hyperbolic phonon polariton electroluminescence is responsible for efficient out-of-plane energy transfer through hBN. We then show that this energy transfer can be engineered using hBN with various turbidity, exhibiting for the first time that far-field energy transfer in turbid media remains valid in the case of energy transfer by confined hyperbolic rays.
Effective cross-sections of nano-objects are fundamental properties that determine their ability to interact with light. However, measuring cross-sections for individual resonators directly and quantitatively remains challenging, particularly because of the very low signals involved. In this contribution, we present how we experimentally measured the thermal emission cross-section of metal-insulator-metal nano-resonators using a hyperuniform distribution based on a hierarchical Poisson-disk algorithm. This method relies on the specific properties of hyperuniform distributions, which ensure that no short-range or long-range correlations between resonators disturb the measured signal.
Modulation spectroscopy enables the investigation of weak infrared radiation signals produced by sources with size is in the micrometer range. We have used this method first to investigate the thermal radiation from single subwavelength sized metallic or dielectric resonators. Next, we have adapted our setup to investigate the radiation from transistors made of graphene microstructures encapsulated in boron nitride (hBN). It is shown that the infrared emission from these devices exhibits features which are typical for electroluminescence and is concomitant with the occurrence of Zener Klein tunneling.
Infrared spatial modulation spectroscopy enables one to acquire background-free spectra of subwavelength sized objects. With this method we have investigated thermally excited single and double metal-insulator-metal plasmonic antennas (MIMs). On single MIMs with silica insulator, the same resonance condition is satisfied at different wavelengths due to the strong dispersion of silica. On double MIMs, the thermal radiation spectra bear the signature of hybridized electromagnetic modes which are simultaneously excited when the gap separation between the antennas is in the 100 nm range.
The electromagnetic modes of a sub-wavelength sized antenna can be excited both optically and through thermal fluctuations. When dealing with individual or a small number of nano-antennas, highly sensitive techniques, such as thermal radiation scanning tunneling microscopy, and infrared spatial modulation spectroscopy, are required in order to extract the very weak emitted thermal radiation. Using these techniques, we have been able to characterize the thermal emission of a single pair of sub-λ metal-insulator-metal antennas separated by a nanometric gap. It is found that the various hybrid modes of a single antenna pair can be simultaneously excited by thermal fluctuations, an essentially incoherent process arising from fluctuating thermal currents.
The effect of hybrid plasmonic modes on the resonant behavior of the considered antenna system may guide future efforts for realizing tunable optical and thermal structures made up of a small number of antennas, for various applications.
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