Near-field Radiative Research Articles

A thermal contact model encompassing near-field effects of multi-interface TEGs in hypersonic conditions

High efficiency heat harvest of hypersonic vehicles claims elaborate design of thermoelectric (TE) conversion process. A thermoelectric generator (TEG) contains multi-interfaces in the heat transfer path and the interfacial thermal contacts with certain amount of nanoscale effects have significant influence on its TE conversion process. In this paper, a thermal contact model encompassing near-field thermal radiation (NFTR) effects of TEGs with heterogeneous interfaces between substrates, electrodes and TE legs is established and experimentally validated in hypersonic conditions. First, a real-topology-based thermal contact resistance (TCR) prediction model is developed and the far- and near-field radiative heat transfer at heterogeneous interfaces is considered by the fluctuational electrodynamics, and the model is validated by direct and indirect experimental measurements. Second, the effects of average interfacial temperature, clearance distance and opposite heat transfer paths on the thermal radiation are analyzed, and the influences of average interfacial temperature, loading pressure and clearance mediums on the TCR are then clarified. Third, the TCR is equivalently considered in a TEG performance evaluation model and the NFTR effects is quantitatively counted. The result shows that: with the consideration of the NFTR, the TCRs between TE legs and electrodes, substrates and electrodes decrease by about 3.90% to 17.0% and 0.510% to 6.40% under vacuum clearance, 1.30% to 5.50% and 0.220% to 2.00% under air clearance, respectively; and the maximum output power of the TEG increases by about 8.02% and 1.29% under vacuum and air clearance (0.1 MPa, 650 K), respectively.

Investigation on near-field radiative heat transfer between two SiC films with different substrates

Near-field radiative heat transfer (NFRHT) has drawn significant attention in the past years due to potential applications in energy harvesting, and information storage. In practical applications, the substrate is necessary to make the structure more stable. However, the investigation of substrate influence on the NFRHT in previous works is rarely carried out. In this work, the influence of the substrate on the NFRHT between two SiC films is investigated. For lossless substrates, the NFRHT is enhanced in thick films (h = 7 nm and h = 20 nm), while suppressed in thin films (h = 1 nm). For lossy substrates, the loss of the substrate can effectively promote the NFRHT. The substrates of real materials are also considered. We find the NFRHT between two SiC films is suppressed, when the substrates are Au and SiO2. The underlying physics mechanism can be explained by the antisymmetric and symmetric mode of surface phonon polaritons (SPhPs) in SiC films, which are analyzed by the energy transmission coefficients (ETCs) as a function of angular frequency and wavevector. In addition, we find that the dispersion relations and ETCs exhibit a good agreement. We believe this work is helpful in understanding the effect of substrates on SPhPs and designing near-field radiation devices.

Near-Field Radiative Heat Transfer between Disordered Multilayer Systems

Near-field radiative heat transfer (NFRHT) research is an important research project after a major breakthrough in nanotechnology. Based on the multilayer structure, we find that due to the existence of inherent losses, the decoupling of hyperbolic modes (HMs) after changing the filling ratio leads to suppression of heat flow near the surface mode resonance frequency. It complements the physical landscape of enhancement of near-field radiative heat transfer by HMs and more surface states supported by multiple surfaces. More importantly, considering the difficulty of accurate preparation at the nanoscale, we introduce the disorder factor to describe the magnitude of the random variation of the layer thickness of the multilayer structure and then explore the effect on heat transfer when the layer thickness is slightly different from the exact value expected. We find that the near-field radiative heat flux decreases gradually as the disorder increases because of interlayer energy localization. However, the reduction in heat transfer does not exceed an order of magnitude, although the disorder is already very large. At the same time, the regulation effect of the disorder on NFRHT is close to that of the same degree of filling ratio, which highlights the importance of disordered systems. This work qualitatively describes the effect of disorder on heat transfer and provides instructive data for the fabrication of NFRHT devices.

Effect of substrate on the near-field radiative heat transfer between α-MoO3 films

Near-field radiative heat transfer (NFRHT) has promising prospects in modern nanotechnology, such as near-field thermal microscopy, nanoscale non-contact thermal management, and information processing. Experimentally, supported substrates are crucial in ensuring structural stability, especially in ultrathin structures. However, the effect of the substrate on the NFRHT has seldom been explored. Here, the NFRHT between α-MoO3 films with different permittivities of substrate is studied. For lossless substrates, the NFRHT is suppressed as the permittivity of the substrate increases when the heat transfer is along the [010] and [100] crystal directions of α-MoO3. When the NFRHT is along the [001] crystal direction of α-MoO3, high-permittivity substrates suppress the NFRHT when the film is thin (< 10 nm), while enhancing the NFRHT in thicker films (> 10 nm). Moreover, we find that the effect of the substrate on the NFRHT highly relies on film thickness. The effect of lossy substrate on NFRHT is also discussed. We find that the loss of the substrate is more significant for the enhancement of heat flux at a small gap distance (20 nm). However, when the gap distance is large (100 nm), the excessive loss suppresses the NFRHT. Hyperbolic polaritons (HPs) can effectively explain the above phenomenon, as confirmed by energy transmission coefficients distribution and dispersion relation in wavevector space. In particular, the volume-confined hyperbolic polaritons play a dominant role in the flux variation between the thin films (1 nm and 10 nm). For the 100-nm film, surface-confined hyperbolic polaritons are more important. This study sheds light on the effect of substrate on HPs and provides theoretical guidance for designing near-field thermal radiation devices.

Substrate effects on the near-field radiative heat transfer between two hBN films

Near-field radiative heat transfer (NFRHT) could surpass the blackbody limit defined by Stefan-Bolzmann’s law by several orders of magnitude, which has potential applications in thermal switching, thermal management, and photovoltaics. To further develop the NFRHT from theory to application, the substrate, which could enhance the stability of the structure, is a critical factor not to be ignored. However, the substrate effect on the NFRHT is still rarely discussed. In this work, we investigate the NFRHT between hexagonal boron nitride (hBN) films with different permittivities of the substrate. Results demonstrate that when the thickness of the film is 1 nm, increasing the permittivity of the substrate will suppress the NFRHT. In contrast, when the thickness of the film is larger (&amp;gt;2 nm), the high-permittivity substrate could enhance the NFRHT. The spectral heat flux (SHF) corresponding to substrates with different permittivities was investigated. The SHF in Type I hyperbolic band of hBN increases with the increase in the permittivity of the substrate, while that in Type II hyperbolic band is completely opposite. This competitive relationship leads to the above-mentioned phenomenon of NFRHT. The underlying physics mechanism can also be explained by the hyperbolic phonon polaritons (HPPs), which are analyzed by the energy transmission coefficients and dispersion relations. The findings in this work will deepen the understanding of the substrate on HPPs and pave a novel way for near-field radiation devices based on hyperbolic materials.

Near-Field Radiative Heat Transfer between $\\beta-$GeSe monolayers: An ab initio study

ABSTRACT We present a theoretical study of the near-field radiative heat transfer (NFRHT) between two -GeSe monolayers, each at a different temperature. (This is a relevant 2D material with superior electron transport and optical properties compared to black-phosphorus monolayers). The required optical conductivity of the monolayer is calculated using density functional theory including spin-orbit coupling, and using the Perdew-Burke-Erzenhof parametrization. Both the intra and interband transitions are taken into account, as well as the contribution of the optical phonons. This allows us to obtain more realistic predictions of the NFRHT between two monolayers of GeSe. The role of the electron doping concentration and the plasma relaxation frequency is investigated, showing a non-monotonic dependence on the radiative heat transfer with increasing doping, and having an optimal doping where the heat flux is maximize. A strong optical anisotropy in the electric conductivity is obtained from the contribution of both electrons and ions This anisotropy is explored, showing that the relative rotation of two monolayers results in modulation of the NFRHT much larger than previously found for similar 2D materials, like -GeSe. As the angle of rotation between the monolayers increases the total heat transfer decreases. Our analysis demonstrates the relevance of properly taking into account the materialelectronic and ionic contributions.

HBN-based regulation of near-field radiative heat transfer between planar structures

Nanoscale thermal regulation plays a vital role in many applications, especially in highly-integrated electronics. In this study, we theoretically analyze the near-field radiation heat transfer within hBN-based planar systems, including bare hBN plates, SiC/hBN plates, graphene/hBN plates and Au/hBN plates. We predict that tailoring the shift frequency of phonon could alter the hyperbolic modes (HMs) of hBN, thus allowing for the coupling and decoupling of HMs with SPhPs of SiC and GSPPs of graphene. Therefore, the radiative heat flux in hBN-based systems except for Au/hBN plates can be greatly regulated, and the regulation ratio can reach 159.6 for bare hBN plates, and above 2 for SiC/hBN plates and for graphene/hBN plates. Results may facilitate understanding of the principles of hBN-based evanescent wave coupling and nanoscale thermal management.

Twist-Induced Near-Field Radiative Heat Switch in Hyperbolic Antiferromagnets

We study the twisted control of the near-field radiative heat transfer between two hyperbolic antiferromagnetic insulators under external magnetic fields. We show that the near-field heat flux can be affected by both the twist angle $\theta$ and the magnitude of the applied magnetic field with different broken symmetries. Irrespective of twist angle, the external magnetic field causes the radiative heat flux to change nonmonotonically, and the minimum heat flux can be found with the magnetic fields of about 1.5 T. Such nonmonotonic behavior is due to the fact that the magnetic field can radically change the nature of the magnon polaritons with time reversal symmetry breaking. The field not only affects the topological structure of surface magnon polaritons, but also induces the volume magnon polaritons that progressively dominate the heat transfer as the field increases. We further propose a twist-induced thermal switch device with inversion symmetry breaking, which can severely regulate radiative heat flux through different magnetic fields. Our findings account for a characteristic modulation of radiative heat transfer with implications for applications in dynamic thermal management.

Metasurfaces Assisted Twisted α-MoO3 for Spinning Thermal Radiation.

Spinning thermal radiation has demonstrated applications in engineering, such as radiation detection and biosensing. In this paper, we propose a new spin thermal radiation emitter composed of the twisted bilayer α-MoO3 metasurface; in our study, it provided more degrees of freedom to control circular dichroism by artificially modifying the filling factor of the metasurface. In addition, circular dichroism was significantly enhanced by introducing a new degree of freedom (filling factor), with a value that could reach 0.9. Strong-spin thermal radiation resulted from the polarization conversion of circularly polarized waves using the α-MoO3 metasurface and selective transmission of linearly polarized waves by the substrate. This allowed for extra flexible control of spinning thermal radiation and significantly enhanced circular dichroism, which promises applications in biosensing and radiation detection. As a result of their unique properties, hyperbolic materials have applications not only in spin thermal radiation, but also in areas such as near-field thermal radiation. In this study, hyperbolic materials were combined with metasurfaces to offer a new idea regarding modulating near-field radiative heat transfer.

Enhancement and Saturation of Near-Field Radiative Heat Transfer in Nanogaps between Metallic Surfaces.

Near-field radiative heat transfer (NFRHT) between planar metallic surfaces was computationally explored over five decades ago by Polder and van Hove [Phys. Rev. B 4, 3303 (1971)PLRBAQ0556-280510.1103/PhysRevB.4.3303]. These studies predicted that, as the gap size (d) between the surfaces decreased, the radiative heat flux first increases by several orders of magnitude until d is ∼100 nm after which the heat flux saturates. However, despite both the fundamental and practical importance of these predictions, the combined enhancement and saturation of NFRHT at small gaps in metallic surfaces remains experimentally unverified. Here, we probe NFRHT between planar metallic (Pt, Au) surfaces and show that RHT rates can exceed the far-field rate by over a thousand times when d is reduced to ∼25 nm. More importantly, we show that for small values of d RHT saturates due to the dominant contributions from transverse electric evanescent modes. Our results are in excellent agreement with the predictions of fluctuational electrodynamics and are expected to inform the development of technologies such as near-field thermophotovoltaics, radiative heat-assisted magnetic recording, and nanolithography.

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.

Near-field radiative heat transfer modulated by nontrivial topological surface states

Three-dimensional topological insulators (3D TIs), such as Bi2Se3 and Bi2Te3, possessing insulating bulk states and nontrivial topological surface states protected by time-reversal symmetry, have attracted considerable attention. In this paper, we investigate the near-field radiative heat transfer in 3D TIs, which can be strongly modulated by the non-trivial surface states. Full 3D TI properties including both the bulk and surface states are considered in our theoretical study. We show that the hybrid polaritons in single-material TI films, resulting from the coupling of Dirac plasmons on the top and bottom surfaces with the multiple phonon polariton modes supported by the bulk states including hyperbolic phonon polaritons (HPP), surface phonon polaritons (SPhP) and epsilon-near-pole (ENP) modes, can strongly mediate and enhance the near-field thermal radiation. The dispersions of hybrid polaritons intensely depend on the chemical potential of the surface and the film thickness, and by tuning both separately, we can control the coupling and competition between the surface and bulk modes, and thus modulate the radiative spectrum and heat flux. In addition, the nonlocal optical response of the surface states has a remarkable impact on the mode hybridization. This work demonstrates the potential of 3D TIs in manipulating near-field thermal radiation, which may provide a useful platform for energy conversion and thermal management.

Photon tunneling reconstitution in black phosphorus/ hBN heterostructure

Excitation of hybrid modes constituted by different material-supported polaritons is a common way to enhance the near-field radiative energy transport, which has fascinating promise in applications of thermal photonics. Here, we investigate near--field thermal radiation mechanisms in heterostructure composed of $h\mathrm{BN}$ film and black phosphorus single layer. The results show that this heterostructured system can give rise to a remarkable enhancement for photon tunneling, outperforming the near-field thermal radiation properties of its building blocks, as well as some other representative heterostructures. Moreover, we find that the anisotropic hybrid effect can induce a remarkable topological reconstitution of polaritons for $h\mathrm{BN}$ film and black phosphorus, forming a novel anisotropic hybrid polaritons. Notably, such hybrid modes show significant topological differences compared to $h\mathrm{BN}$ film and black phosphorus in the type-I Reststrahlen band due to the anisotropic anticrossing hybridization effect. Lastly, we systematically analyze the evolution of such hybrid polariton modes as a function of $h\mathrm{BN}$ film thickness and the corresponding influence on radiative properties of the heterostructure. This work may benefit the applications of near-field energy harvesting and radiative cooling based on hybrid polaritons in anisotropic two-dimensional material and hyperbolic film.

Nonlocal composite metamaterial in calculation of near-field thermal rectification.

We consider the near-field radiative heat transfer (NFRHT) between a semi-infinite polar dielectric plate and a composite metamaterial containing semiconductor nanoparticles with spatial dispersion or nonlocality. We show that the enhancement of near-field heat radiation is found owing to the strong coupling of surface phonon polaritons (SPhPs) excited between polar dielectric plate and air, and localized surface plasmon polaritons (LSPPs) in the composite metamaterials. The introduction of nonlocality is helpful to enhance the NFRHT and even the rectification efficiency significantly when the temperature difference is small. For a large volume fraction of semiconductor nanoparticles, the thermal rectification efficiency can be larger than 90% at a small temperature difference within 150 K. Our findings may pave a way for thermal devices based on composite metamaterial containing semiconductor nanoparticles.

Active Control of Near-Field Radiative Heat Transfer Between InSb and Graphene Multilayered Magneto-Optical Metamaterials

We theoretically investigate the active control of the near-field radiative heat transfer (NFRHT) between two multilayered metamaterials consisting of alternating two kinds of magneto-optical materials, i.e., graphene and InSb. The active control of NFRHT can be realized by applying an external perpendicular magnetic field. We found that, when the chemical potential of graphene μ is 0.05 eV or 0.1 eV, the surface magneto-plasmon polaritons (MPPs) gradually split, and one part moves toward higher frequencies with the increase of the magnetic field. When H = 7 T, the relative thermal magnetoresistance ratio is as high as 82.2% compared with the zero field for μ = 0.05 eV. And most importantly, due to the strong coupling between the MPPs of graphene and the surface modes of InSb, when μ = 0.7 eV, the heat flux reaches 286% compared with the zero field by changing the magnetic field to 1 T. In addition, the effect of the thicknesses of InSb, period number and vacuum gap on heat transfer are also investigated. Through the combined effect of the external magnetic field, the chemical potential of graphene and other factors on the local surface electromagnetic modes, the active control of the NFRHT between two multilayered metamaterials can be realized.

Thermal Switching of Near-Field Radiative Heat Transfer Between Nanoparticles via Multilayered Surface Modes

We theoretically demonstrate near-field radiative thermal switching between two nanoparticles located above a multilayered slab. We propose a multilayered structure composed of $\mathrm{Si}\mathrm{C}$ and the phase transition material ${\mathrm{VO}}_{2}$. The high tunability of the multilayered structure enables the active modulation of surface polaritons when combined with the phase transition feature of ${\mathrm{VO}}_{2}$, overcoming the intrinsic resonance of the thermal radiation of ${\mathrm{VO}}_{2}$. Utilizing this feature, the surface polaritons enormously excited at the particle's resonant frequency above the multilayer can be switched on or off, resulting in the efficient modulation of heat flux between nanoparticles. The effects of interparticle distance and multilayer parameters on thermal switching ratios are investigated. We demonstrate that the multilayer with metallic ${\mathrm{VO}}_{2}$ can significantly inhibit the heat flux between particles as a result of the destructive interference between direct and reflected waves. The excited surface modes above the multilayer with insulating ${\mathrm{VO}}_{2}$ can still improve the heat flux between nanoparticles, resulting in a thermal switching ratio of ${10}^{\ensuremath{-}5}$ at the particle resonant frequency at a large interparticle distance.

Effective Approximation Method for Nanogratings-induced Near-Field Radiative Heat Transfer.

Nanoscale radiative thermal transport between a pair of metamaterial gratings is studied within this work. The effective medium theory (EMT), a traditional method to calculate the near-field radiative heat transfer (NFRHT) between nanograting structures, does not account for the surface pattern effects of nanostructures. Here, we introduce the effective approximation NFRHT method that considers the effects of surface patterns on the NFRHT. Meanwhile, we calculate the heat flux between a pair of silica (SiO2) nanogratings with various separation distances, lateral displacements, and grating heights with respect to one another. Numerical calculations show that when compared with the EMT method, here the effective approximation method is more suitable for analyzing the NFRHT between a pair of relatively displaced nanogratings. Furthermore, it is demonstrated that compared with the result based on the EMT method, it is possible to realize an inverse heat flux trend with respect to the nanograting height between nanogratings without modifying the vacuum gap calculated by this effective approximation NFRHT method, which verifies that the NFRHT between the side faces of gratings greatly affects the NFRHT between a pair of nanogratings. By taking advantage of this effective approximation NFRHT method, the NFRHT in complex micro/nano-electromechanical devices can be accurately predicted and analyzed.

An intermediate modulator enhanced the near-field thermal radiation of semiconductor vanadium dioxide

We theoretically investigate a three-body near-field radiative heat transfer (NFRHT) system, which consists of three separated parallel plates with different temperatures and certain vacuum spacing. The emitter (body1) and the receiver (body3) are both composed of a monolayer graphene and a VO2 film covered by semi-infinite bulk SiO2. The intermediate (body2) has a composite graphene/VO2/graphene heterostructure. The steady temperature of body2 can be determined based on the fact that the near-field radiative heat flow (NFRHF) emitted by body1 is equal to that received by body3 at thermal steady state. NFRHF can be highly tuned by changing the vacuum gap and the chemical potential of graphene in the three-body system. This paper can provide theoretical guidance for experimental and practical applications of near-field thermal radiation, and are significant for the applications of NFRHT structures containing intermediates in the field of temperature control.

Near-Field Radiative Heat Transfer between Weyl Semimetal Multilayers

Near-Field Radiative Heat Transfer between Weyl Semimetal Multilayers

Eigenmode Analysis of Dynamical Many-Body Near-Field Radiative Heat Transfer Mediated by an External Magnetic Field

Eigenmode Analysis of Dynamical Many-Body Near-Field Radiative Heat Transfer Mediated by an External Magnetic Field