Photon Tunneling Research Articles

Enhanced near-field radiative heat transfer between borophene sheets on different substrates

Abstract Near-field radiative heat transfer (NFRHT) has the potential to exceed the blackbody limit by several orders of magnitude, offering significant opportunities for energy harvesting. In this study, we have examined the NFRHT between two borophene sheets through the calculation of heat transfer coefficient (HTC). Due to the tunneling of evanescent waves, borophene sheet allows for enhanced heat flux and adjustable NFRHT by varying its electron density and electron relaxation time. Additionally, the near field coupling is further examined when the borophene is deposited on dielectric or lossy substrates. The maximum HTC is closely related to the real part of the dielectric substrate. As a case study, the HTC on the lossy substrate of MoO3, ZnSe and SiC are calculated for comparison. Our results indicate that MoO3 is the optimal substrate to get the enhanced energy transfer coefficient. It results in a remarkable value of 1737 times higher than the blackbody limit owing to the enhanced photon tunneling probability. Thus, our study reveals the effect of substrate on the HTC between borophene sheets and provides a theoretical guidance for the design of near-field thermal radiation devices.

Ultrahigh Thermal Rectification at Small Temperature Difference Achieved by Near‐Field Thermal Photon Manipulation

AbstractThermal diodes, which allow heat to flow in a preferential direction, are an essential component of thermal circuitry and will find applications in many fields ranging from thermal photon controls to quantum information. The quality of a thermal diode is defined by the thermal rectification ratio (TRR). Here, an ultrahigh TRR exceeding 105 at a small temperature difference (1–5 K) is presented based on near‐field thermal photon (NFTP) manipulation, by utilizing asymmetric gap‐variated dual terminals based on graphene/Si heterostructures and materials with contrasting thermal expansion coefficients. Analyses of the photon tunneling probability show that the colossal TRR comes from coupled and decoupled graphene surface plasmon polaritons under opposite temperature biases, remaining robust across a wide operating temperature range. Further enhancement can be achieved by tuning the Fermi level of graphene. This work demonstrates the significance of asymmetry in NFTP manipulation for thermal diode performance, achieving an ultrahigh TRR, which is at least three orders higher than the state‐of‐the‐art structures at the same small temperature difference (1–5 K), and is comparable to state‐of‐the‐art electronic diodes.

Random Lasing under Dissipative Tunneling Conditions in a Network Quantum Material

A new mechanism of the generation of a random laser based on a random photonic network with dissipative tunneling of photons between microcavities that are placed at the nodes of such network and contain identical two-level quantum systems has been revealed. It has been shown that an additional source of photon losses in tunneling promotes the separation of individual modes of the random laser and the achievement of the lasing threshold even at a vanishingly small population inversion. In this case, the enhancement of laser modes has an interference nature and is due to the energy redistribution between the nodes of the photonic network that correspond to different signs of the frequency detuning of stationary modes of the random laser from the transition frequency of two-level systems. It has been shown that the traditional lasing mechanism, which demonstrates features of the spectrum of single microcavities, i.e., is almost independent of the topological properties of the network and the tunneling parameter, is present in the region of zero detuning.

Enhancement and modulation of near-field radiative heat transfer in Bi2Se3/graphene-based three-body configurations

The manipulation of near-field radiative heat transfer (NFRHT) through complex photon tunneling in many-body systems has garnered significant attention, particularly for advancing thermal management in micro- and nanodevices. In this work, we theoretically investigate the enhancement and modulation of NFRHT within a graphene/Bi2Se3-based three-body configuration. Compared to a two-body configuration, the three-body modulator enhances the near-field radiative heat flux (NFRHF) by 2.77, primarily due to the enhancement of surface plasmon polaritons facilitated by graphene. Moreover, we analyze how NFRHF is modulated by varying the vacuum gap between the emitter and the intermediate, adjusting the thickness of Bi2Se3 films in emitter and intermediate, as well as manipulating the chemical potentials of graphene. Results indicate that by tuning the chemical potentials of graphene, thermal regulation can be enhanced up to a ratio of 2.55. This enhancement is attributed to the excitation of SPPs, which are concentrated in a narrower wave vector space and higher angular frequency range as the chemical potential of graphene increases. These findings have implications for controlling thermal radiation applications utilizing graphene and Bi2Se3 heterostructures. This work demonstrates the superiority of the three-body system in enhancing NFRHT and contributes new insights into the potential applications of Bi2Se3 in NFRHT.

Near-field radiative heat transfer between graphene-covered Weyl semimetals

Polariton manipulations introduce novel approaches to modulate the near-field radiative heat transfer (NFRHT). Our theoretical investigation in this study centers on NFRHT in graphene-covered Weyl semimetals (WSMs). Our findings indicate variable heat flux enhancement or attenuation, contingent on chemical potential of graphene. Enhancement or attenuation mechanisms stem from the coupling or decoupling of surface plasmon polaritons (SPPs) in the graphene/WSM heterostructure. The graphene-covered WSM photon tunneling probabilities variation is demonstrated in detail. This research enhances our comprehension of SPPs within the graphene/WSM heterostructure and suggests methods for actively controlling NFRHT.

Resonant Tunneling of Photons in Layered Optical Nanostructures (Metamaterials)

Resonant Tunneling of Photons in Layered Optical Nanostructures (Metamaterials)

Active control of nonreciprocal near-field radiative heat transfer with a drift-current biased graphene/α-MoO3 heterostructure.

The interaction between the drift-current biased graphene plasmonics and the hyperbolic phonon polaritons of α-MoO3 provides a promising way to manipulate near-field radiation heat transfer (NFRHT). Through examination of the drift biased graphene/α-MoO3 heterostructure, it has been discovered that drift-current applied to the graphene effectively enhances photon tunneling. Consequently, they dynamically modulate the coupling effect of the two excitations, thereby offering a reliable pathway for the modulation of NFRHT. Furthermore, the influencing mechanism of vacuum gaps on nonreciprocal NFRHT with different drift-current rates is revealed, and it is discovered that the vacuum gaps can filter the nonreciprocal surface plasmon polaritons with high nonreciprocity. Our findings make it possible to manipulate nanoscale thermal rectification and noncontact thermal modulation.

Analysis of near field radiation among lithography-free metal-dielectric-metal perfect absorbers with a combined numerical method

An integrated analysis is developed to determine the far-field and near-field radiation of lithography-free metal-dielectric-metal (MIM) structures. Directional spectral emissivity determined with the integrated analysis shows good agreement with the directional spectral absorptivity from verified full wave simulation. With the integrated analysis, we identified that the condition of Fabry–Perot resonance used to design broadband wide-angle perfect light absorbers/emitters with MIM structures could trigger the waveguide modes of the dielectric layer. The waveguide modes can amplify the thermal electric field for photon tunneling between two MIM structures across a 100 nm level gap. Adding an additional pair of waveguides that can amplify evanescent waves in the gap formed with two MIM structures can further enhance the strength of photon tunneling. The enhanced photon tunneling shows high-intensity quasi-monochromatic near-field radiation in TM mode across a 100 nm gap at specific wavelengths. We expect even stronger photon tunneling for high-intensity quasi-monochromatic near field radiation across a more significant gap can occur when the MIM structure made with lower loss metal is combined with structures providing stronger amplification of evanescent wave.

Photon tunneling mechanism of internal plasmon polaritons between two thick slabs under near-field radiation excitation

Internal plasmon polariton (IPP), featuring localization of electromagnetic fields in the interior of material, is recently revealed to be supported in slabs with gradient carrier density distribution under near-field thermal excitation. However, the dispersion relation and photon tunneling mechanism of IPP have not been fully elucidated. To address the issues, in this paper, we investigate the photon tunneling mechanism of IPPs both in the symmetric and asymmetric gradient systems of two thick slabs at the near-field configuration with thermal excitation. It is revealed that infinite modes of IPP are supported in the gradient slabs. The frequencies of these IPP modes are highly space-dependent. They poorly couple to each other and collectively contribute to the photon tunneling with respective trade-off wavevectors and tunneling probabilities. For asymmetric systems where the slab at one side is replaced by that of uniform carrier density, we find the resonance locking effect of IPP. Moreover, the photon tunneling spectrum can be tailored by the gradient layer and the vacuum gap sizes. The mechanism outlined here deepens our understanding of IPPs as well as offers guidance for the design of nanoscale devices with tunable carrier density.

Effectiveness of multi-junction cells in near-field thermophotovoltaic devices considering additional losses

Abstract Thermophotovoltaic (TPV) energy converters hold substantial potential in converting thermal radiation from high-temperature emitters into electrical energy through photovoltaic (PV) cells, offering applications ranging from solar energy harvesting to waste heat recovery. Near-field TPV (NF-TPV) devices, focused on enhancing power output density (POD), exhibit unique potential by harnessing photon tunneling. However, this potential can be mitigated by additional losses arising from high photocurrent densities and corresponding scalability issues. This study comprehensively investigates the effectiveness of multi-junction-based NF-TPV devices, accounting for additional losses. We propose two approximative expressions to quantify the impact of additional losses and characterize current density-voltage curves. Verification against rigorously optimized results establishes a criterion for effective performance. Our method provides precise POD estimations even for devices with 10 or more subcells, facilitating performance analysis across parameters like vacuum gap distance, cell width, emitter temperature, and the number of subcells compared to far-field counterparts. This research outlines a roadmap for the scalable design of NF-TPV devices, emphasizing the role of multi-junction PV cells. The analytical framework we developed will provide vital insights for future high-performance TPV devices.

Performance analysis of photon-enhanced thermionic emission systems mediated by quantum tunneling

Reducing the gap between the electrodes to the nanoscale and utilizing quantum effects are an effective way to enhance the performance of a thermionic energy device. In this work, we establish the model of a photon-enhanced thermionic emission system with a nanoscale vacuum gap, where the electron transport due to electron tunneling and the near-field radiation resulting from photon tunneling are introduced. Analytical expressions for the thermionic emission current, electron tunneling current, and heat flux due to the near-field radiation are provided. By using the energy and particle balance equations, the electron concentration and the temperature of the cathode are determined. The impacts of the voltage, electron affinity, and gap distance on the performance are further analyzed. Results show that the suggested system can achieve high efficiency at the low-temperature cathode. Up to 34.7% of solar-to-electricity efficiency is possible at a cathode temperature of 472.5 K. The proposed model provides a strategy for designing highly efficient thermionic emission devices operating at low temperatures.

Microscopic Hamiltonian and chaotic behavior for Barium Titanate nanoparticles revealed by photonic tunneling model

In order to understand the microscopic properties of the ferroelectric nanoparticles, we review concepts of the attractive BaTiO3 crystals where a photon field from its constituent electrons and ions are considered. We present an associated Hamiltonian and extended potential which are the bases of the physical description of the system from certain geometry of the semiquantal space with the specific phonon mode. Furthermore, we formulate the nonlinear dynamics equation of the systems with the famous microscopic Hamiltonian and Heisenberg equation of motion. In addition, we interest ourselves to a system of BaTiO3 crystals and hypothesis leading to order-disorder nature of phase transitions. The latter are linked to the cooperative phenomenon of chains. The numerical simulations reveal that complex behaviors propagate in such system that can be useful for future application of Barium Titanate crystals in modern electronic technologies.

Medium-Bridge Near-Field Thermophotovoltaic System

ABSTRACT The energy conversion performance of thermophotovoltaic (TPV) systems can be improved when the vacuum gap between the emitter and the TPV cell is at the near-field owing to the photon tunneling of evanescent waves. Among them, the back-gapped-reflector TPV systems have gained interest as a method of improving their conversion efficiency by optimizing the spectral absorption of TPV cells. In this work, we introduce an alternative concept for the back-gapped-reflector TPV systems, namely the medium-bridge near-field TPV system, by building a medium bridge between the metal reflector and the TPV cell using SU8 nanofilm. The SU8 medium-bridge achieves a noticeable improvement in output performance by increasing the spectral absorption of the InAs cell and reducing parasitic absorption losses of the Au substrate. The results indicate that, as a consequence of the improved effect of the medium-bridge, the output power density and efficiency of this system exceed those of the conventional TPV system (which lacks a medium-bridge) by 26.4% and 36.5%, respectively. Moreover, we systematically analyze the modulation of medium-bridge thicknesses and cell thickness on output performance and clarify how both affect energy losses of this near-field TPV system. Our work offers a strategy to improve the energy conversion performance of the near-field TPV system, opening new opportunities for developing near-field energy conversion.

Amplification of near field radiation at surfaces of pure dielectric domain with anti-reflection films and photonic crystal structures

With chemical stability under high temperatures, dielectric materials can be idealized thermal emitters for different energy applications. However, dielectric materials do not support surface waves at near-infrared ranges for longer-distance thermal photon tunneling, which limits their applications in near-field thermal radiation. It is demonstrated in this study that thermal field amplification at near-infrared wavelengths at dielectric surfaces could be achieved through asymmetric Fabry–Perot resonance with anti-reflection coatings or 1D photonic crystal type structures. ⩾100 nm near-infrared thermal photon tunneling can be achieved when these thin film structures are added to the emitter and the collector surfaces. Among these two thin film structures, 1D photonic crystal type periodic structures constructed with the same high refractive index material as the emitter/collector material allow near-field thermal photon tunneling at large parallel wavenumbers. Moreover, the field amplification can be increased by adding more 1D photonic crystal layers to achieve even longer distances near field thermal photon tunneling.

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

Abstract 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.

Role of the Nottingham effect in heat transfer in the extreme near-field regime

We analyze the heat transfer between two metals separated by a vacuum gap in the extreme near-field regime. In this cross-over regime between conduction and radiation, heat exchanges are mediated by photon, phonon and electron tunneling. We quantify the relative contribution of these carriers with respect to both the separation distance between the two bodies and the applied bias voltage. In the presence of a weak bias ($V_{\rm b}<100$~mV), electrons and phonons can contribute equally to the heat transfer near contact, while the contribution of photons becomes negligible. On the other hand, for larger bias voltages, electrons play a dominant role. Moreover, we demonstrate that depending on the magnitude of this bias, electrons can either cool down or heat up the hot body by the Nottingham effect. Our results emphasize some inconsistencies in recent experimental results about heat exchanges in the extreme near-field regime and set a road map for future experiments.

Резонансное туннелирование фотонов в слоистых оптических наноструктурах (метаматериалах)

The conditions of resonant (almost complete) tunneling of photons (plane monochromatic electromagnetic waves) through layered dielectric and metal-dielectric structures are considered. Resonant tunneling occurs at frequencies at which the resonance conditions for the corresponding structures of open resonators are met. For metal-dielectric structures, the possibility of tunneling in the optical range with a strong barrier in the IR range is shown, which can be used to control the transmission of window panes.

Resonant tunneling of photons in layered optical nanostructures (metamaterials)

The conditions of resonant (almost complete) tunneling of photons (plane monochromatic electromagnetic waves) through layered dielectric and metal-dielectric structures are considered. Resonant tunneling occurs at frequencies at which the resonance conditions for the corresponding structures of open resonators are met. For metal-dielectric structures, the possibility of tunneling in the optical range with a strong barrier in the IR range is shown, which can be used to control the transmission of window panes. Keywords: dielectric permittivity, homogenization, resonant tunneling, plasmons, metal nanoparticles, window panes.

Coupling interactions of anisotropic hyperbolic phonon polaritons in double layered orthorhombic molybdenum trioxide

The natural hyperbolic phonon polariton material-orthorhombic molybdenum trioxide (α-MoO&lt;sub&gt;3&lt;/sub&gt;) has recently attracted much interest , due to the associated ultra-confinement of light and enhanced light-matter interactions. We theoretically propose and study the in-plane anisotropic phonon polaritons (APhPs) in the Kretschmann structure with monolayer and dual layers α-MoO&lt;sub&gt;3&lt;/sub&gt;. The excitation of phonon polaritons and the corresponding dispersion properties in this multilayer system are studied by using a generalized 4×4 transfer matrix method (TMM). The frequency dispersions with geometrical parameters are also discussed in detail. The results confirm that the interlayer coupling can be modulated by stacking the multilayer films and regulating the thickness of each layer. More interestingly, when the distance between double α-MoO&lt;sub&gt;3&lt;/sub&gt; layers is much smaller than the propagation length of PhPs, a strong coupling phenomenon occurs, and the photon tunneling probability and intensity can be greatly improved. When the incident angle is greater than the total internal reflection angle, the phase matching condition for SPhP excitation can be satisfied. Within the 40° incident angle, the SPhP blue-shifts rapidly with the increase of incident angle. But then the dispersion curve no longer changes with increase of incidence angle. The enlargement of the interstitial layer can also lead the Fabry-Perot (FP) resonance mode to be excited. The APhP in layered heterostructure is an important part of today's nanophotonic technology, our study can help optimize and design tunable optoelectronic devices based on hyperbolic materials.

Enhanced near-field thermal radiation between black phosphorus with high electron density by BP/hBN heterostructures

ABSTRACT The black phosphorus (BP)/hexagonal boron nitride (hBN) Van der Waals heterostructure has great potential application in BP-based devices due to its higher stability than monolayer BP film. The near-field thermal radiation (NFTR) between two identical BP/hBN heterostructures with high electron density is studied to promote the application of BP-based devices. The BP/hBN heterostructures show a higher heat transfer coefficient (HTC) at a 10 nm gap distance compared to BP films with electron density n larger than 1 × 1013 cm−2, due to the coupling of surface plasmon polaritons (SPPs) and hyperbolic phonon polaritons (HPPs). Especially at n ≥ 3 × 1013 cm−2, the improvement is more than 100%. The SPPs and the HPPs couple into surface plasmon-phonon polaritons (SPPPs) out of the hyperbolic region and hyperbolic plasmon-phonon polaritons (HPPPs) inside. The SPPPs can achieve photon tunneling in the broader wavevector region than SPPs, making most of the contribution to heat transfer. The influences of the thickness of the hBN sheet and gap distance are also discussed. This scheme only effectively enhances NFTR for BP with high electron density at small nanogaps. After structural optimization, h = 2 nm is the optimal thickness for BP/hBN configuration with low electron density, such as n = 1 × 1013 cm−2. In contrast, large thickness h = 500 nm is optimal for BP with high electron density. At high electron density, a thick hBN sheet is prominent in enhancing the SPPPs in the frequencies below the type-I region and the HPPPs inside the type-II region. We further propose BP/hBN/BP heterostructures and find that HTC is further enhanced by 4.4% ~ 30.8% due to the more robust surface modes. Our work may contribute to developing BP-based near-field thermal devices and promote understanding the NFTR mechanism of BP/hBN heterostructure.