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Near-field radiative heat transfer (NFRHT) between multilayer graphene/hBN heterostructures has been demonstrated to exceed the blackbody limit due to the coupling mechanism of surface plasmon polaritons and hyperbolic phonon polaritons, opening the door to applications in thermal management, thermophotovoltaics, and nanoscale metrology. Recent studies have shown that adding vacuum layers within multilayer structures can effectively promote surface modes and thus enhance NFRHT. However, the influence of vacuum layers on NFRHT between multilayer graphene/hBN heterostructures has not been investigated. Moreover, the influence of vacuum layers on coupled resonance modes excited in multilayer structures is worth discussing. In this work, we study the NFRHT based on multilayer graphene/vacuum/hBN/vacuum structures. The results show that as the gap distance increases from 20 nm to 100 nm, the NFRHT of three-cell and six-cell configurations is enhanced, while that of unit-cell configuration is suppressed. The potential mechanism can be identified as the excitation of surface plasmon-phonon polaritons (SPPPs) and hyperbolic plasmon-phonon polaritons (HPPPs) in multilayer structures. The enhancement factor of the six-cell configurations is up to 4.82 when the gap distance is 80 nm. Moreover, the influences of the chemical potential of graphene and the layer thickness on the NFRHT are discussed. The interesting results in this work indicate the perspectives for future near-field research involving coupling of SPPPs and HPPPs, and shed new light on high-performance devices introducing vacuum layers based on near-field radiative heat transfer. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials and their vertically stacked heterostructures have attracted much attention due to their novel optical properties and strong light-matter interactions in the infrared. Here, we present a theoretical study of the near-field thermal radiation of 2D vdW heterostructures vertically stacked of graphene and monolayer polar material (2D hBN as an example). An asymmetric Fano line shape is observed in its near-field thermal radiation spectrum, which is attributed to the interference between the narrowband discrete state (the phonon polaritons in 2D hBN) and a broadband continuum state (the plasmons in graphene), as verified by the coupled oscillator model. In addition, we show that 2D van der Waals heterostructures can achieve nearly the same high radiative heat flux as graphene but with markedly different spectral distributions, especially at high chemical potentials. By tuning the chemical potential of graphene, we can actively control the radiative heat flux of 2D van der Waals heterostructures and manipulate the radiative spectrum, such as the transition from Fano resonance to electromagnetic-induced transparency (EIT). Our results reveal the rich physics and demonstrate the potential of 2D vdW heterostructures for applications in nanoscale thermal management and energy conversion. [ABSTRACT FROM AUTHOR]

• MD and first-principles calculations derived parameters for thermal radiation. • Simulations revealed temperature variations due to microthermal sources. • Interface structures improved the continuity and stability of heat diffusion. • Phonon-polaritons stabilized thermal transport in micro- and nanoscale gaps. • Nonlinear effects emerged due to high-energy-level heat source values. The thermal transmission properties of polymer-based composites, commonly used in satellites, are crucial for high-precision thermal management applications. The study constructed the structures of polyimide polymers and polyimide/graphene interfaces based on molecular dynamics and fluctuation dissipation theorem. Optical parameters were determined through first-principles calculations, and the thermal transport from a microthermal source was simulated using Reverse Non-Equilibrium Molecular Dynamics (RNEMD) and the modified four-dimensional transfer matrix method (M4D-TMM). Simulations of polymers, interface structures, and interfacial thermal radiation models investigated the transmission dynamics of microthermal sources during heat transport. Findings showed that the differences in the temperature fields formed within the polymer from microthermal heat sources were less than 20 K for heat source inputs ranging from 0.002 W/m² to 20 GW/m². With a microthermal source, the heat diffusion was extensive, the heat transport was continuous, and the temperature field remained stable. At the level of the heat source up to the intermolecular energy level, the temperature field distribution showed significant instability, leading to nonlinear effects. Within the interface structure, the continuity of heat diffusion increased as the heat source intensified. The interface structure demonstrated enhanced temperature sensitivity and improved stability, with minimal fluctuations of only 0.59 %. The increase in heat flux perpendicular to the interface structure was ascribed to near-field radiative heat transfer. As the temperature difference decreased to less than 0.1 K, the influence of evanescent waves on radiative heat flux nearly disappeared. Phonon polaritons maintained temperature stability during thermal transport through micro- and nanoscale gaps. Integrating thermal conduction principles in polyimide polymers and interface structures with near-field thermal radiation provides a theoretical framework for high-precision thermal management in gravitational wave detection. [ABSTRACT FROM AUTHOR]

Dynamic modulation of near-field radiative heat transfer (NFRHT) requires changing the optical responses of the object, which is expected to be realized with the help of the strain engineering. Based on the electric dipole approximation and the reflection Green's function, in this work, we investigate the effect of the hBN film under uniform in-plane strain on the NFRHT between two graphene/SiC core-shell (GSCS) nanoparticles. By changing the magnitude of the strain on the film, the hyperbolic phonon polaritons (HPPs) can be dynamically tuned to match and deviate from the localized surface resonance (LSR), thus significantly modulating the NFRHT between the nanoparticles. When the two GSCS nanoparticles are placed above a strained hBN film, an amplification of the maximum radiative heat flux by about 6 orders of magnitude can be achieved. In addition, after the introduction of graphene to form graphene/hBN heterostructure, the radiative heat flux can be further enhanced with the help of the hybrid polaritons. Especially at a suitable chemical potential and strain, the NFRHT can be enhanced by 4 more orders of magnitude compared to the bare hBN film. This work provides a new insight into efficient and dynamic thermal management among nanoparticles. • Dynamic modulation of NFRHT between two graphene/SiC core-shell nanoparticles induced by strained hBN is investigated. • The HPPs of the substrate can be coupled and decoupled with the LSR of the nanoparticles under the effect of strain. • The modulation contrast can reach almost 5000 when the optimal strain is applied to the hBN film. • The hybrid polaritons supported by graphene/hBN heterostructure help to maintain higher radiative heat flux. [ABSTRACT FROM AUTHOR]

• NFRHT between two multilayered graphene/porous SiC terminals is studied. • Multiple polaritons and their coupling are capable of enhancing near-field flux. • Heat flux is a combination result of the multiple polaritons and the medium loss. • An upper flux enhancement limitation exists for increasing the layer number. • Multiple polaritons-mediated NFRHT mechanisms and regulations are presented. Near-field radiative heat transfer (NFRHT) between two separated terminals can enhance the heat flux determined by blackbody theory by several orders of magnitude. In this work, we study the NFRHT between two terminals made of periodic multilayered graphene/porous silicon carbide (SiC), specifically focusing on the multiple surface polariton effects. The two terminals are parallel and separated by a vacuum gap. The porous SiC-supported surface phonon polaritons (SPhPs) and hyperbolic phonon polaritons (HPhPs), and their coupling with the graphene-supported surface plasmon polaritons (SPPs) leads to apparent enhancement of the radiative heat flux between the gapped terminals. The underlying mechanism of multiple polaritons for amplifying the near-field heat flux is revealed through the energy transmission coefficients for different scenarios. Results show that the heat flux between the multilayered terminals is a combination result of the multiple surface polaritons and the medium loss. When the vacuum gap is set as d = 10 nm, the heat flux between the 50-layered terminals is 1.48 times that between the single-layered terminals. We demonstrate that the NFRHT can be dynamically controlled and optimized by appropriately engineering the number of layers, the chemical potential of graphene, and the porosity and thickness of the porous SiC sheet. This work paves an alternative controllable structure for strengthening and regulating NFRHT and thus has potential applications in micro-nanoscale thermal management. [ABSTRACT FROM AUTHOR]

• We have proposed a data-driven machine learning workflow for designing multilayer hyperbolic metamaterials composed of α-MoO 3 , achieving high modulation contrast in near-field thermal radiation. • By combining the multilayer perceptron and bayesian optimization techniques, we optimize the rotation angle, layer thickness, and gap distance of the multilayer metamaterials, resulting in a 97 % improvement in thermal modulation contrast compared to previous single layer structures. • The large thermal modulation contrast is attributed to the controlled alignment and misalignment of hyperbolic plasmon polaritons and hyperbolic surface phonon polaritons in each layer, achieved by manipulating the rotation angles. The thermal modulator based on the near-field radiative heat transfer has wide applications in thermoelectric diodes, thermoelectric transistors, and thermal storage. However, the design of optimal near-field thermal radiation structure is a complex and challenging problem due to the tremendous number of degrees of freedom. In this work, we have proposed a data-driven machine learning workflow to efficiently design multilayer hyperbolic metamaterials composed of α-MoO 3 for near-field thermal radiative modulator with high modulation contrast. By combining the multilayer perceptron and Bayesian optimization, the rotation angle, layer thickness and gap distance of the multilayer metamaterials are optimized to achieve a maximum thermal modulation contrast ratio of 6.29. This represents a 97 % improvement compared to previous single layer structure. The large thermal modulation contrast is mainly attributed to the alignment and misalignment of hyperbolic plasmon polaritons and hyperbolic surface phonon polaritons of each layer controlled by the rotation. The results provide a promising way for accelerating the designing and manipulating of near-field radiative heat transfer by anisotropic hyperbolic materials through the data-driven style. [Display omitted] [ABSTRACT FROM AUTHOR]

• The near-field radiative heat transfer between multilayer structures composed of different hyperbolic materials is investigated. • The total heat flux between multilayer structures is enhanced compared to that between hBN (19-fold) and α -MoO 3 (1.46-fold) films. • The underlying physical mechanism is that vacuum layers promote the strong coupling of hyperbolic phonon polaritons supported by different hyperbolic materials. Near-field radiative heat transfer (NFRHT) has drawn significant interest in the recent years, including thermal management and energy harvesting. The NFRHT between single hyperbolic materials (HMs) has been thoroughly investigated. However, the research on the NFRHT between periodic multilayer structures composed of different HMs is rarely discussed. Moreover, the coupling effect of hyperbolic phonon polaritons (HPPs) supported by different HMs is still unclear. In this work, we investigated the NFRHT between multilayer structures composed of hexagonal boron nitride (hBN) and α -phase molybdenum trioxide (α -MoO 3), separated by vacuum layers. The influence of the gap distance, the unit-cell number, the thickness of the HMs and thickness of the vacuum layer on the NFRHT are discussed. The numerical results show that the maximal total heat flux (THF) between six-cell multilayer structures is 19 times compared to the THF between hBN films at the gap distance of 50 nm and is 1.46 times compared to the THF between α -MoO 3 films at the gap distance of 30 nm. Such enhancement can also be found at other similar gap distances. The vacuum layer promotes the coupling of HPPs supported by different HMs, which can be elucidated by the energy transmission coefficients. This work could benefit the application of near-field thermal radiative devices based on HMs. [ABSTRACT FROM AUTHOR]

• We study the radiative heat transfer between two nanoparticles placed above the thin dielectric film. • The surface mode of thin film can strongly couple with the particle resonance. • The presence of the SiC thin film produces four orders of magnitude of amplification in heat transfer between two particles. • We address the role of the interparticle distance in the enhancement effect of heat flux by analyzing the SPhPs propagation length. • The thin film intensifies the SPhPs-SPPs coupling between SiC and doped Si particles,significantly enhancing heat-transfer between two particles with dissimilar materials. We study the radiative heat transfer between two nanoparticles placed above the thin film under the framework of the dipole approximation and reflection Green's function. We show a high enhancement of heat transfer between particles, owing to the antisymmetric and symmetric surface modes excited at a wide band. The presence of the SiC thin film produces four orders of magnitude of amplification for the case of SiC particles which support the localized surface phonon polaritons (SPhPs). Enhancement is caused by the intense surface modes excited at the particle resonance and further proved through spectral analysis. The thin film can also provide an enhancement at a considerable distance, different from the huge inhibitory effect exhibited in the semi-infinite slab case. We address the role of the interparticle distance in the enhancement of heat flux by analyzing the SPhPs propagation length above the thin film. Finally, we show the thin film can intensify the coupling between SiC and doped Si particles, bringing out a high enhancement of radiative heat transfer between two particles with dissimilar materials. This enhancement is also attributed to the strong antisymmetric modes that amplify the emitted electric field energy density in the half-space from the SiC particle. This type of strong amplification can play an essential role in thermal tuning in the nanoparticle system. [ABSTRACT FROM AUTHOR]

• Modulation of near-field radiative heat transfer with rotated anisotropic hBN and α-MoO 3 nanoparticles are investigated. • The LHPP modes have also been investigated by analyzing the spectral heat power and electric field energy density. • The effects of size parameter and material of the nanoparticles on the modulation factor have been studied. • The modulation effect (up to ∼ 12,000) of biaxial material α-MoO 3 is better than that of the uniaxial material hBN, and is 10-fold larger than the state of the art. Modulation of near-field radiative heat transfer (NFRHT) with rotated anisotropic hBN and α-MoO 3 nanoparticles (NPs) are investigated. The spectral heat power, total heat power and electric field energy density are calculated at different particle orientations. Numerical results show that the modulation factor of the α-MoO 3 NPs could be up to ∼12,000 with particle radius of 40 nm at a gap distance of 200 nm, which is ∼ 10-fold larger than the state of the art. Excitation of localized hyperbolic phonon polaritons (LHPPs) in different particle orientations allow for the excellent modulation. The modulation factor of the hBN NPs is 5.9 due to the insensitivity of the LHPPs in the type II hyperbolic band to the particle orientations. This work might be helpful in designing a high performance near-field radiative modulator in particle systems. [ABSTRACT FROM AUTHOR]

The hybridization of surface plasmon polaritons and hyperbolic phonon polaritons in graphene/hBN heterostructures has been well documented to achieve very high radiative heat flux transferred in the near field, paving the way for wide applications ranging from energy harvesting, non-contact thermal management to thermal imaging. However, previous related theoretical studies mainly focused on suspended structures. When it comes to the experimental implementation, a supporting substrate is quite a necessity for this kind of 2D layered heterostructures to ensure structural stability. Herein, the near-field radiative heat transfer (NFRHT) between bi-planar graphene/hBN heterostructures was revisited by integrating them with various substrates, including Au, SiC, and silica, under the framework of the fluctuation-dissipation theorem. The results show that each substrate exerts significant impacts either further enhancing or suppressing the NFRHT between those bi-planar heterostructures, due to the competition between polaritonic couplings and dielectric losses. Whereas, these substrate effects depend on the hBN thickness with a critical length, beyond which the hBN itself is thick enough to indiscriminately screen all these effects. The findings in this study will be instructive to both the experimental designs and device integrations for graphene-based NFRHT applications. [ABSTRACT FROM AUTHOR]