Optimized Colossal Near-Field Thermal Radiation Enabled by Manipulating Coupled Plasmon Polariton Geometry

Colossal Near-Field Radiative Heat Transfer Mediated by Coupled Polaritons with an Ultrahigh Dynamic Range

Near-field radiative heat transfer (NFRHT) can exceed the blackbody limit by several orders of magnitude owing to the tunneling evanescent waves. Exploiting this near-field enhancement holds significant potential for emerging technologies. It has been suggested that coupled polaritons can give rise to orders of magnitude enhancement of NFRHT. However, a thorough experimental verification of this phenomenon is still missing. Here this work experimentally shows that NFRHT mediated by coupled polaritons in millimeter-size graphene/SiC/SiO2 composite devices in planar plate configuration can realize about 302.8 ±  35.2-fold enhancement with respect to the blackbody limit at a gap distance of 87  ±  0.8 nm. The radiative thermal conductance and effective gap heat transfer coefficient can reach unprecedented values of 0.136 WK-1 and 5440 Wm-2K-1. Additionally, a scattering-type scanning near-field optical measurement, in conjunction with full-wave numerical simulations, provides further evidence for the coupled polaritonic characteristics of the devices. Notably, this work experimentally demonstrates dynamic regulation of NFRHT can be achieved by modulating the bias voltage, leading to an ultrahigh dynamic range of ≈4.115. This work ambiguously elucidates the important role of coupled polaritons in NFRHT, paving the way for the manipulation of nanoscale heat transport, energy conversion, and thermal computing via the strong coupling effect.

Enhanced near-field radiative heat transfer between core-shell nanoparticles through surface modes hybridization

Core-shell nanoparticles (CSNPs) are widely used in energy harvesting, conversion, and thermal management due to the excellent physical properties of different components. Because of the synergistic interaction between the core and the shell, the thermal radiative properties are expected to be further enhanced. In this work, we achieve near-field radiative heat transfer (NFRHT) enhancement between SiC@Drude CSNPs. Numerical results show that the total heat flux between NPs is 1.47 times and 9.98 times higher than homogeneous SiC and Drude NPs at the same radius when the core volume fraction is 0.76. Surface modes hybridization arising from the interfaces of the shell-core and shell-air contributes to the improved thermal radiation. The effect of shift frequency on the NFRHT between SiC@Drude CSNPs is studied, showing that the enhancement ratio of NFRHT between CSNPs can reach 4.34 at a shift frequency of 1 × 1014 rad/s, which is 38.34 times higher than the previous work. This study demonstrates that surface modes hybridization in CSNPs can significantly improve NFRHT and open a novel path for high-efficiency energy transport at the nanoscale.

Unconventional Thermophotonic Charge Density Wave

Charge-order states of broken symmetry, such as charge density wave (CDW), are able to induce exceptional physical properties, however, the precise understanding of the underlying physics is still elusive. Here, we combine fluctuational electrodynamics and density functional theory to reveal an unconventional thermophotonic effect in CDW-bearing TiSe_{2}, referred to as thermophotonic-CDW (tp-CDW). The interplay of plasmon polariton and CDW electron excitations give rise to an anomalous negative temperature dependency in thermal photons transport, offering an intuitive fingerprint for a transformation of the electron order. Additionally, the demonstrated nontrivial features of tp-CDW transition hold promise for a controllable manipulation of heat flow, which could be extensively utilized in various fields such as thermal science and electron dynamics, as well as in next-generation energy devices.

Hollow g-C3N4@Ag3PO4 Core-Shell Nanoreactor Loaded with Au Nanoparticles: Boosting Photothermal Catalysis in Confined Space

Low solar energy utilization efficiency and serious charge recombination remain major challenges for photocatalytic systems. Herein, a hollow core-shell Au/g-C3N4@Ag3PO4 photothermal nanoreactor is successfully prepared by a two-step deposition method. Benefit from efficient spectral utilization and fast charge separation induced by the unique hollow core-shell heterostructure, the H2 evolution rate of Au/g-C3N4@Ag3PO4 is 16.9 times that of the pristine g-C3N4, and the degradation efficiency of tetracycline is increased by 88.1%. The enhanced catalytic performance can be attributed to the ordered charge movement on the hollow core-shell structure and a local high-temperature environment, which effectively accelerates the carrier separation and chemical reaction kinetics. This work highlights the important role of the space confinement effect in photothermal catalysis and provides a promising strategy for the development of the next generation of highly efficient photothermal catalysts.

Ultra-broadband and wide-angle nonreciprocal thermal emitter based on Weyl semimetal metamaterials

Nonreciprocal thermal radiation can violate Kirchhoff's law and exhibit different emissivity at symmetric polar angles relative to the normal direction. Realizing a mid-infrared broadband nonreciprocal thermal emitter with a wide emission angle range is a fundamental yet challenging task, particularly without the need for an external magnetic field. Here, we propose a nonreciprocal thermal emitter operating in the mid-infrared that achieves a significantly nonreciprocal thermal radiation in a wavelength range from 12 μm to 20 μm, spanning a wide angular range from 16° to 88°. This is achieved by utilizing a multilayered Weyl semimetal (WSM)/dielectric structure, which takes the advantage of the strong nonreciprocity of WSMs with different Fermi levels and epsilon-near-zero-induced Brewster modes. The results provide a wider angular range in the broad mid-infrared band compared to previous attempts. The robustness of the nonreciprocal radiation is confirmed through wavelength-averaged emissivity across the azimuth angle φ range from 0° to 360°. Some possible materials and nanostructures as dielectric layers are discussed, showcasing the flexibility and reliability of the design. This work holds promising potential applications such as enhanced radiative cooling, thermal emitters for medical sensing and infrared heating, energy conversion, etc.

Observation of Near-Field Thermal Radiation between Coplanar Nanodevices with Subwavelength Dimensions

With the continuous advancement of nanotechnology, nanodevices have become crucial components in computing, sensing, and energy conversion applications. The structures of nanodevices typically possess subwavelength dimensions and separations, which pose significant challenges for understanding energy transport phenomena in nanodevices. Here, on the basis of a judiciously designed thermal photonic nanodevice, we report the first measurement of near-field energy transport between two coplanar subwavelength structures over temperature bias up to ∼190 K. Our experimental results demonstrate a 20-fold enhancement in energy transfer beyond blackbody radiation. In contrast with the well-established near-field interactions between two semi-infinite bodies, the subwavelength confinements in nanodevices lead to increased polariton scattering and reduction of supporting photonic modes and, therefore, a lower energy flow at a given separation. Our work unveils exciting opportunities for the rational design of nanodevices, particularly for coplanar near-field energy transport, with important implications for the development of efficient nanodevices for energy harvesting and thermal management.

Coupling polaritons in near-field radiative heat transfer between multilayer graphene/vacuum/α-MoO3/vacuum heterostructures

Both materials and structures can significantly affect radiative heat transfer, which is more pronounced in the near-field regime of two-dimensional and hyperbolic materials, and has promising prospects in thermophotovoltaics, radiative cooling, and nanoscale metrology. Hence, it is important to investigate the near-field radiative heat transfer (NFRHT) in complicated heterostructures consisting of two-dimensional and hyperbolic materials. Recent studies have reported that adding vacuum layers to multilayer structures can effectively enhance the NFRHT. Take the case of multilayer graphene/α-MoO3 heterostructures: the effect of vacuum layers on these heterostructures has not been studied, and hence investigations on adding vacuum layers between graphene and α-MoO3 layers should be emphasized. In this work, we conduct an investigation of the NFRHT between multilayer graphene/vacuum/α-MoO3/vacuum heterostructures. Compared to unit graphene/α-MoO3 heterostructures without vacuum layers, it is found that NFRHT between the heterostructures with vacuum layers can be suppressed to 49.1% when the gap distance is 10 nm, and can be enhanced to 16.3% when the gap distance is 100 nm. These phenomena are thoroughly explained by the coupling of surface plasmon polaritons and hyperbolic phonon polaritons. Energy transmission coefficients and spectral heat flux are analysed during the calculations changing chemical potentials of graphene, thicknesses of vacuum layers, and α-MoO3 layers. This study is expected to provide guidance in implementing the thermal management of reasonable NFRHT devices based on graphene/α-MoO3 heterostructures.

Dirac semimetal-assisted near-field radiative thermal rectifier and thermostat based on phase transition of vanadium dioxide

The near-field thermal radiation has broad application prospects in micro-nano-scale thermal management technology. In this paper, we report the Dirac semimetal-assisted (AlCuFe quasicrystal) near-field radiative thermal rectifier (DSTR) and thermostat (DST), respectively. The DSTR is made of a Dirac semimetal-covered vanadium dioxide (VO2) plate and silicon dioxide (SiO2) plate separated by a vacuum gap. The left and right sides of DST are consisted of the SiO2 covered with Dirac semimetal, and the intermediate plate is the VO2. The strong coupling of the surface electromagnetic modes between the Dirac semimetal, SiO2, and insulating VO2 leads to enhance near-field radiative transfer. In the DSTR, the net radiative heat flux of VO2 in the insulating state is much larger than that in metallic state. When the vacuum gap distance d=100 nm, Fermi level EF=0.20 eV, and film thickness t=12 nm, the global rectification factor of DSTR is 3.5, which is 50% higher than that of structure without Dirac semimetal. In the DST, the equilibrium temperature of the VO2 can be controlled accurately to achieve the switching between the metallic and insulating state of VO2. When the vacuum gap distance d=60 nm, intermediate plate thickness δ=30 nm, and film thickness t=2 nm, with the modulation of Fermi level between 0.05-0.15 eV, the equilibrium temperature of VO2 can be controlled between 325-371 K. In brief, when the crystalline state of VO2 changes between the insulating and metallic state with temperature, the active regulation of near-field thermal radiation can be realized in both two-body and three-body parallel plate structure. This work will pave a way to further improve performance of near-field radiative thermal management and modulation.

Nonlocal Near-Field Radiative Heat Transfer by Transdimensional Plasmonics

Using transdimensional plasmonic materials (TDPM) within the framework of fluctuational electrodynamics, we demonstrate nonlocality in dielectric response alters near-field heat transfer at gap sizes on the order of hundreds of nanometers. Our theoretical study reveals that, opposite to the local model prediction, propagating waves can transport energy through the TDPM. However, energy transport by polaritons at shorter separations is reduced due to the metallic response of TDPM stronger than that predicted by the local model. Our experiments conducted for a configuration with a silica sphere and a doped silicon plate coated with an ultrathin layer of platinum as the TDPM show good agreement with the nonlocal near-field radiation theory. Our experimental work in conjunction with the nonlocal theory has important implications in thermophotovoltaic energy conversion, thermal management applications with metal coatings, and quantum-optical structures.

Polariton hybridization phenomena on near-field radiative heat transfer in periodic graphene/α-MoO3 cells

Coupling of surface plasmon polaritons (SPPs) supported by graphene and hyperbolic phonon polaritons (HPPs) supported by hyperbolic materials (HMs) could effectively promote photon tunneling, and hence the radiative heat transfer. In this work, we investigate the polariton hybridization phenomena on near-field radiative heat transfer (NFRHT) in multilayer heterostructures, which consist of periodic graphene/α-MoO3 cells. Numerical results show that increasing the graphene/α-MoO3 cells can effectively enhance the NFRHT when the vacuum gap is less than 50 nm, but suppresses the enhanced performance with larger gap distance. This depends on the coupling of SPPs and HPPs in the periodic structure, which is analyzed by the energy transmission coefficients distributed in the wavevector space. The influence of the thickness of the α-MoO3 film and the chemical potential of graphene on the NFRHT is investigated. The findings in this work may guide designing high-performance near-field energy transfer and conversion devices based on coupling polaritons.

Near-Field Radiative Heat Transfer Modulation with an Ultrahigh Dynamic Range through Mode Mismatching

Modulating near-field radiative heat transfer (NFRHT) with a high dynamic range is challenging in nanoscale thermal science and engineering. Modulation depths [(maximum value - minimum value)/(maximum value + minimum value) × 100%] of ≈2% to ≈15.7% have been reported with matched modes, but breaking the constraint of mode matching theoretically allows for higher modulation depth. We demonstrate a modulation depth of ≈32.2% by a pair of graphene-covered SU8 heterostructures at a gap distance of ≈80 nm. Dissimilar Fermi levels tuned by bias voltages enable mismatched surface plasmon polaritons which improves the modulation. The modulation depth when switching from a matched mode to a mismatched mode is ≈4.4-fold compared to that when switching between matched modes. This work shows the importance of symmetry in polariton-mediated NFRHT and represents the largest modulation depth to date in a two-body system with fixed gap distance and temperature.

Enhancement and Manipulation of Near-Field Thermal Radiation Using Hybrid Hyperbolic Polaritons

Owing to a high electromagnetic confinement and a strong photonic density of states, hyperbolic surface plasmon polaritons (HSPPs) provide a fascinating promise for applications in thermal photonics. In this work, we theoretically predict a possibility for the improvement of the near-field radiative heat transfer on the basis of tailoring the electromagnetic state of hyperbolic metasurfaces by the uniaxial hyperbolic substrate. By using the photonic tunneling coefficient and the polaritons dispersion, we present a comprehensive study of the hybrid effect of the hyperbolic substrate on HSPPs. We find that due to the hybrid effect of the hyperbolic substrate, the anisotropy surface state of hyperbolic metasurfaces would undergo significant deformations and even topological transition. Moreover, we systematically exhibit the evolution of such hybrid hyperbolic mode with different thicknesses of the hyperbolic substrate and analyze the thickness effect on radiative properties of the hybrid system. It is shown that the resulting heat transfer with the assistance of the hybrid hyperbolic mode by optimizing the substrate parameters is many times stronger than that of monolayer hyperbolic metasurface at the same vacuum gap. Taken together, our results provide a platform to tailor 2D hyperbolic plasmons as a potential strategy toward passive or active control of the near-field heat transfer, and the hybrid hyperbolic mode presented here may facilitate the system design for near-field energy harvesting, thermal imaging, and radiative cooling applications.

Enhanced Near-Field Radiative Heat Transfer between Graphene/hBN Systems

Near-field radiative heat transfer (NFRHT) can exceed the blackbody radiation limit owing to the coupled evanescent waves, implying a significant potential for energy conversion and thermal management. Coupled surface plasmon polaritons (SPPs) and hyperbolic phonon polaritons (HPPs) with small ohmic losses enable a long propagation wavelength that is essential in NFRHT. However, so far, there still lacks knowledge about the experimental investigation of the coupling of SPPs and HPPs in terms of NFRHT. In this study, the NFRHT between graphene/hexagonal boron nitride (hBN) systems that can be readily transferred onto various substrates, with a gap space of ≈400 nm is measured. NFRHT enhancements in the order of three and six times higher than the blackbody limit for graphene/hBN heterostructures and graphene/hBN/graphene multilayers, respectively are demonstrated. In addition, the largest ever radiative heat flux using graphene/hBN/graphene multilayers under similar gap space of 400 nm is obtained. Consequently, analyzing the photon tunneling modes reveal that these phenomena are consequences of coupled SPPs of graphene and HPPs of hBN.

Optical axis-driven modulation of near-field radiative heat transfer between two calcite parallel structures

Recently, the increasing research on the anisotropic optical axis (OA) has provided a novel way to control light. However, this method is rarely applied to modulate the near-field radiative heat...