Plasmonic Thermal Emitter Research Articles

High-performance long-wavelength infrared switchable stealth based on In3SbTe2 metasurface

Metasurface based on phase change material (PCM) for switchable thermal radiation is of great significance to the application of infrared (IR) stealth and thermal management in multi-scenario. However, the previously reported results based on GST and VO2 metasurface face the challenges of relatively low intrinsic loss in metallic state and weak stability, respectively. In this paper, we have designed a plasmonic metasurface thermal emitter (PMTE) based on the PCM of In3SbTe2 (IST), which can manage the thermal emissivity in the wavelength range of 5–14 μm as the IST changes from the amorphous to the crystalline state. For IST in the amorphous state, the PMTE's average emissivity in the wavelength ranges of 5–8 μm and 8–14 μm, are 0.22 and 0.44 respectively, which can be used for the long-wavelength IR (LWIR) stealth of object with low temperature in high-temperature environment. For IST in the crystalline state, the PMTE's average emissivity in the wavelength ranges of 5–8 μm and 8–14 μm, are 0.68 and 0.14 respectively, which can achieve radiative heat dissipation and LWIR stealth of object with high temperature in low-temperature environment. We displayed simulated infrared images of the PMTE in amorphous and crystalline states to demonstrate its switchable LWIR stealth at different temperatures. In addition, the radiative heat dissipation properties of the PMTE are discussed. Our proposed PMTE based on IST can be potentially applied to IR stealth and thermal management in different scenarios.

Multi-mode resonance plasmonic solar absorber based on pyramid multiary-grating

In the manuscript, a broad-band perfect absorber based on multilayer-grating and MDM film structure is proposed and numerically studied. Finite difference time domain (FDTD) simulations indicate the absorption performances are originated from Fabry–Perot (FP) resonance effect, localized, and propagating surface plasmons (LSPs and PSPs) effect. The designed absorber possesses over 95% absorption from 697 nm to 2906 nm, and an average absorption of 98.7% is achieved with TM-polarized. For TM-polarized, the designed absorber possesses over 95% between 534 nm and 2475 nm when the oblique-angle is up to 45°, while for a TE-polarized light, the corresponding average absorption remains 80.48% when the oblique-angle is up to 30°. The average absorption is larger than 94% in different environment refractive indexes (1 < RI < 1.5), which illustrates the designed absorber possesses excellent environment RI stability. Another absorber with triple layer grating of different sizes is also designed, and the absorber has more than 95% absorption between 400 nm and 2376 nm, based on the high absorption and waveband, the absorber can find potential applications in solar energy capture. It is believed the proposed work can be applied in plasmonic solar absorber design, thermal emitter, and plasmonic imaging.

High-efficient plasmonic solar absorber and thermal emitter from ultraviolet to near-infrared region

In this paper, the design and analysis of an ultra-broadband solar absorber based on the combination of two TiN metasurface resonators are presented. The absorber comprises a periodic array of combined TiN disk-square ring resonators located on a stack of TiO2/TiN films. The proposed absorber shows a high average absorption of 94% in the wavelength range of 250–3000 nm and provides a continuous bandwidth of 2200 nm (i.e., 250 nm to 2450 nm) for the absorption above 90%. The effects of geometrical parameters and the oblique incidences for both TE- and TM-polarized incident light on the absorption are discussed. Also, the impact of using other plasmonic metals instead of TiN is investigated. Simulation results obtained by the finite-difference time-domain (FDTD) method indicate a high absorption of about 80%, even for an oblique incidence up to 50° for both polarizations. Having outstanding properties like high absorption, ultra-wide bandwidth, independence to irradiance polarization, and insensitivity to radiation angle make the presented solar absorber a promising choice for various high-temperature applications like energy harvesting and emitting.

Switching plasmonic resonance in multi-gap infrared metasurface absorber using vanadium dioxide patches

Reconfigurable metasurface absorbers enable collecting or emitting radiation within selected frequency bands. It is thus necessary to decipher such behavior for many applications, including plasmonic energy harvesting, radiative cooling and thermal emitters. In this article, we propose a compact reconfigurable vanadium dioxide (VO2)-based metasurface absorber/emitter to demonstrate switching between dual and single-band absorption modes in the mid-infrared regime. The unit cell of the design employs a four-split gold circular ring resonator with gaps filled with VO2 patches. The phase-transition property of VO2 between semiconductor and metallic states is used to control the mode of operation of the metasurface absorber. When VO2 is in the semiconductor state, a dual-band absorption at 6 μm and 10.6 μm is obtained. When it attains a metallic state, the metasurface exhibits a single-band absorption at 8.25 μm. To achieve the maximum absorption efficiency in both single and dual-band modes, adaptive wind-driven optimization was employed as a global optimization technique. The proposed absorber provides polarization-independent behavior for both Transverse Electric and Transverse Magnetic polarizations. Moreover, the proposed design shows above 80% absorptance for incidence angle up to 45° for the dual-band mode, and up to 35° for the single-band mode. When operating the absorber as a tunable emitter, a switching of 79% in emissivity is achieved at 8.25 μm. These favorable findings may facilitate the development of important devices for temperature regulation, smart windows, and thermal imaging.

Polarization switching of thermal emissions based on plasmonic structures incorporating phase-changing material Ge2Sb2Te5

The ability to control the polarization of thermal emissions is important for fundamental science and many applications such as multichannel infrared emitters and chemical sensing. Most previous works on controlling the polarization of thermal emission are based on changing geometric sizes of the structures. The active control remains elusive so far. Here, we propose a design to actively switch the polarization of thermal emission. A metal-insulator-metal plasmonic thermal emitter with phase changing material Ge2Sb2Te5 (GST) as the insulator is experimentally demonstrated. The thermal emitter with top GST and gold ellipses can excite third-order magnetic resonances with perpendicular polarization along both short radius and long radius. The polarization of the thermal emission can be rotated by 90° at 9.55 μm peak wavelength when GST phase changes from the amorphous phase to the 40% crystalline phase.

Narrowband Wavelength Selective Thermal Emitters by Confined Tamm Plasmon Polaritons

This study experimentally demonstrates infrared wavelength selective thermal emission based on Tamm plasmon polaritons (TPPs). Unlike conventional TPP structures, which have a thin metal layer on a distributed Bragg reflector (DBR), the proposed structure has a thick metal under a DBR that is more robust for thermal radiation. The number of DBR pairs is a critical factor in maximizing the narrowband emission needed to satisfy the impedance matching condition, which varies with the choice of metal film. Optimum designs for four different metals, aluminum, gold, molybdenum, and tungsten, are presented. The temporal coupled-mode theory was introduced to explain the origin of the high Q-factor of the proposed structure, which can achieve a twice higher Q-factor for the measured emissivity compared to typical plasmonic thermal emitters. The structure is one-dimensional, consisting of only multilayers and free from nanopatterning, offering a practical design in applications such as gas sensing, narrowband IR so...

Plasmonic Thermal Emitters for Dynamically Tunable Infrared Radiation

Periodic bimetallic microstructures using nickel and gold are fabricated on an elastomeric substrate by use of strain‐induced buckling of the metallic layers, which can be compatible with roll‐to‐roll manufacturing. The intrinsically low emissivity of gold in the midinfrared regime is selectively enhanced by the surface plasmonic resonance at three different midinfrared wavelengths, 4.5, 6.3, and 9.4 µm, respectively, which directly correspond to the structural periodicities of the metallic microstructures. As the thermal emission enhancement effect exists only for the polarization perpendicular to the orientation of the microstructures, substantially polarized thermal emission with an extinction ratio close to 3 is demonstrated. Moreover, the elastically deformed plasmonic thermal emitters demonstrate strain‐dependent emission peaks, which can be applied for future mechano–thermal sensing and dynamic thermal signature modulation.

Thermal graphene metamaterials and epsilon-near-zero high temperature plasmonics

The key feature of a thermophotovoltaic (TPV) emitter is the enhancement of thermal emission corresponding to energies just above the bandgap of the absorbing photovoltaic cell and simultaneous suppression of thermal emission below the bandgap. We show here that a single layer plasmonic coating can perform this task with high efficiency. Our key design principle involves tuning the epsilon-near-zero frequency (plasma frequency) of the metal acting as a thermal emitter to the electronic bandgap of the semiconducting cell. This approach utilizes the change in the reflectivity of a metal near its plasma frequency (epsilon-near-zero frequency) to lead to spectrally selective thermal emission, and can be adapted to large area coatings using high temperature plasmonic materials. We provide a detailed analysis of the spectral and angular performance of high temperature plasmonic coatings as TPV emitters. We show the potential of such high temperature plasmonic thermal emitter coatings (p-TECs) for narrowband near-field thermal emission. We also show the enhancement of near-surface energy density in graphene-multilayer thermal metamaterials due to a topological transition at an effective epsilon-near-zero frequency. This opens up spectrally selective thermal emission from graphene multilayers in the infrared frequency regime. Our design paves the way for the development of single layer p-TECs and graphene multilayers for spectrally selective radiative heat transfer applications.

Quasi-coherent thermal radiation with multiple resonant plasmonic cavities

This paper proposes a 1D plasmonic multilayer structure as a high-contrast mid-infrared thermal emitter with three distinct resonant wavelengths. The three resonance modes, based on the localized surface plasmon, provide an omnidirectional thermal emission. The emissivity spectrum reveals high polarization and strongly angle-independent properties. The resonance-assisted emissivity can be as high as 19.5 dB relative to off-resonant sideband emissivity. Such extremely low sideband emissivity makes the proposed plasmonic thermal emitter an efficient, high-contrast emitter, which will be useful for thermophotovoltaic and thermal sensing applications.

Triple-wavelength infrared plasmonic thermal emitter using hybrid dielectric materials in periodic arrangement

This paper presents a triple-wavelength infrared plasmonic thermal emitter using a periodic arrangement of hybrid dielectric materials within a tri-layer metal/dielectric/metal structure. The proposed arrangement makes it possible to sustain multiple resonance of localized surface plasmons (LSP), thereby providing an additional degree of freedom by which to vary the resonant wavelengths in the medium infrared region. Variations in the effective refractive index due to the different modal distribution within dielectric gratings results in multiple LSP resonances, and the resonant wavelengths can be easily tuned by altering the compositions of hybrid dielectric materials. The measured dispersion relation diagram and the finite difference time domain simulation indicated that the resonances were localized. They also indicate that the magnetic fields generated by the multiple LSP modes exhibit distribution patterns similar to that of a standing wave in the periodic arrangement of the hybrid dielectric layer, each of which presents an emission peak corresponding to a different modal order.

Dielectric function dependence on temperature for Au and Ag

The dielectric functions of Au and Ag are measured using a spectral ellipsometer. The temperature dependence parameters ωp, τ, and ε∞, in the Drude–Sommerfeld model have been studied. Furthermore, we provide an empirical function to describe the temperature dependence of the dielectric function for Au and Ag. The empirical function shows a good agreement with previous results. Through the empirical function, one can obtain the dielectric constant at arbitrary temperature and wavelength. This database is useful for the applications that use surface plasmon (SP) resonance at high temperatures, such as the plasmonic thermal emitter, SP-assisted thermal cancer treatment and so on.

Double wavelength infrared emission by localized surface plasmonic thermal emitter

A double wavelength infrared emission by plasmonic thermal emitter using stacked Au/SiO2/Au/SiO2/Au structure was investigated. The effective refractive index of sandwiched SiO2 is higher than normal value due to the coupling of surface plasmons at the top and bottom Au/SiO2 interfaces. Two different localized surface plasmon modes were excited with the same metal width, but different SiO2 layer thicknesses in top and bottom Au/SiO2/Au tri-layer structures. The measured dispersion relation diagram and simulation demonstrated that the resonances were localized resonance and the distribution of magnetic field was concentrated at the central SiO2 layer between two Au layers.

Improved Performance of Plasmonic Thermal Emitter via Incorporation of Gold Nanoparticles

The improved performance of plasmonic thermal emitter by incorporating randomly distributed gold nanoparticles is demonstrated in the mid-infrared range. Gold films with different thicknesses were deposited on top of the devices and then annealed to form separate nanoparticles. Experimental results showed that the size and distribution of nanoparticles depend mainly on the gold film thickness, rather than annealing temperature. It is observed that thermal emitters with smaller particles embedded exhibit significant enhancement in emission intensity. It is the strong scattering between gold nanoparticles that contributes to the enhanced infrared thermal emission. As an efficient mid-infrared radiation source, this device has the potential to be applied in various fields such as second harmonic generation of infrared source and biosensors.

Emission Enhancement in Ag/${\rm SiO}_{2}$/Ag Thermal Emitter by Using a Hexagonal Dimple Array

This letter describes the successful fabrication of a novel tri-layer Ag/SiO2/Ag plasmonic thermal emitter with circular and square hole shapes at top silver film arranged in a hexagonal dimple array. The proposed design improves the emission intensity and reduces the full width half maximum. Experimental results indicate that the proposed design increases the emission intensity at 200°C from 30.5 to 42.3 mW/cm2 for the hexagonal circular hole array, as well as increases the same intensity from 43.3 to 79.3 mW/cm2 for the hexagonal square hole array.

Significantly enhanced transmission achieved with double-layered metallic aperture arrays with sub-skin-depth Ag film

We present both theoretical and experimental investigation on significantly enhanced transmission through (Ag/Au) double-layered metallic aperture arrays with sub-skin-depth Ag film due to the coupling role of a surface plasmon polariton at the Ag/Au interface by evanescent waves. The results indicate that the enhanced transmittance is highly dependent on the Ag film thickness. When the Ag film thickness increases, the peak transmittance firstly increases and then decreases. Moreover, other metal material properties are also discussed. The highest peak transmittance is obtained when the Ag film thickness is 4 nm. The finite-difference time-domain simulations agree well with the experimental results. This finding provides an effective way to control the enhanced transmission for double-layered metallic aperture arrays, which has potential applications in designing a high-performance plasmonic thermal emitter.

Triple Peaks Plasmonic Thermal Emitter with Selectable Wavelength Using Periodic Block Pattern as Top Layer

A plasmonic thermal emitter with a periodic block pattern as the top layer was investigated. It is found that by adjusting the length and orientation of the rectangle metallic islands inside the block pattern, three polarization-dependent peaks can be obtained in the thermal radiation spectra. The individual mode can be extracted according to the different polarizations by an external polarizer. In addition, the device can be designed to emit in the desired wavelength range by tuning the dimensions of the block pattern.

The effect of narrow bandwidth infrared radiation on the growth of Escherichia coli

While broad band infrared has a number of biomedical applications, the effects with specific wavelengths on biomolecule remain unclear. In this study, narrow band infrared plasmonic thermal emitters with peak wavelengths from 3.0 to 5.0 μm were developed to irradiate Escherichia coli (E. coli) cultures for 24 h. It was found that with peak wavelengths at 4.0, 4.5, and 5.0 μm, they could promote the growth of cells. Systems biology analyses were performed to investigate the underlying molecular mechanisms. Furthermore, specific wavelengths (4.0-5.0 μm) induced the expression of transporters and enzymes involved in metabolism and respiration, thus stimulating the proliferation of E. coli.

The effect of array periodicity on the filtering characteristics of metal/dielectric photonic crystals

We present a both theoretical and experimental investigation into the effect of array periodicity on the filtering characteristics of metal/dielectric photonic crystals (MDPhCs) with hexagonal arrays of subwavelength holes in gold/silicon dioxide films, varying the array periodicity from 6 to 8 μm every 1 μm while the ratio of hole radius to array periodicity is kept constant (1/4). The results indicate that the reflectance spectrum is highly dependent on the array periodicity. When the array periodicity increases, the reflectance spectrum exhibits a large redshift regularly. The finite difference time domain (FDTD) simulations agree well with the experimental results. By analyzing the relationship between the position of the reflectance minimum and the array periodicity, we find that the filtering characteristics of MDPhCs have an almost linear relationship with the array periodicity under the conditions of keeping the same ratio of hole radius to array periodicity (1/4). This finding provides an effective way to control the filtering characteristics of MDPhCs, which have potential applications in optical filters, plasmonic thermal emitters and so on.

Nanoamorphous carbon as a blackbody source in plasmonic thermal emitters

Ag/dielectric/Ag-type plasmonic thermal emitters (PTEs) following a hexagonal lattice were fabricated, and their plasmonic emission spectrums were characterized with Fourier transform infrared spectroscopy. Nanoamorphous carbon (NAC) is used as a dielectric layer. Doping NAC with various materials over a wide range of levels enables control of the resistivity of the composite films where MoSi(2) was selected as the dopant. Wavelength tuning in the range of 4-7 μm is demonstrated by changing the conductivity of the composite films as well as the lattice periodicity of the hexagonal lattice. We also tested the mechanical stability of the PTEs under mechanical strains.

Emission properties of Ag/dielectric/Ag plasmonic thermal emitter with different lattice type, hole shape, and dielectric material

The emission spectra of the trilayer Ag/dielectric/Ag plasmonic thermal emitter (PTE) with different lattice type, hole shape, and dielectric material were investigated. It is found that the position and number of thermal emission peak of the PTE are determined by the lattice type not by the hole shape and dielectric materials. The PTE with hexagonal lattice generates only one strong (1,0) Ag/dielectric emission peak, whereas a similar PTE with square lattice generates two strong (1,0) and (1,1) Ag/dielectric emission peaks, their relative intensities follow the blackbody radiation law. This phenomenon suggests the coupling of Ag/dielectric and Ag/air modes.