Search

In this paper, we have designed a solar absorber with ultra-broadband absorption. The structure has seven layers with a metal-dielectric periodic film stack and a metallic copper substefficiency. The metal-dielectric periodic membrane stack and the dielectric are continuous to form a metal/dielectric composite microstructure. It has a very high absorption efficiency at 280 nm–2893 nm. The absorption efficiency in this wavelength range is 96.26% and absorption efficiency at AM 1.5 is up to 95.66% by finite difference time domain method (FDTD) simulation. The thermal radiation absorption efficiency of the structure is 93.69% at 1000K and 94.5% at 1200 K, which can also be used in the manufacture of the heat sink due to its high thermal radiation absorption efficiency. Our proposed solar absorber has good incidence angle insensitivity (0°–60°) and good polarization independence (0°–90°). These advantages enable our absorbers to be widely used for solar absorption and emission and offer a variety of design options for ideal absorbers. • The absorber enables ultra-broadband high-efficiency absorption. • The absorber has ultra-high thermal emission efficiency. • The absorber is insensitive to changes in the angle of incidence and the angle of polarization. [ABSTRACT FROM AUTHOR]

A gold-coated D-shape photonic crystal fibre sensor based on surface plasmon resonance (PCF-SPR) is designed with microfluidic channels and numerically investigated for detection of a wide range of refractive indexes. The D-type structure and microfluidic channels improve the performance of the sensor by reducing the distance between the core and channel and increasing the coupling strength of the fundamental and plasmonic modes. By optimizing the structural parameters, the PCF-SPR sensor can realize a broad range of detection for low RIs changing from 1.23 to 1.36. The maximum spectral sensitivity of 18,000 nm/RIU and optimal resolution of 5.56 × 10−6 RIU are observed for RIs between 1.35 and 1.36. The sensor is capable of detecting analytes with RIs below 1.36 and has great potential in medical diagnosis, drug development, food safety, and water testing. [ABSTRACT FROM AUTHOR]

A novel ring anti-resonance fibre (ARF) is designed and demonstrated for the transmission of orbital angular momentum (OAM) modes. The fibre consists of two layers of negative curvature tubes arranged orderly inside and outside the ring region and OAM modes can be transmitted in the ring region. The properties of the fibre are investigated by the finite element method based on the COMSOL multiphysics software and a manufacturing method is proposed. The fibre shows stable transmission of 30 OAMs in the 1.5–1.6 μm band, low and flat dispersion (5.98 ps/(km nm)), extremely small nonlinear coefficient (0.539 km−1 W−1 at 1.55 μm) and confinement loss (10−9–10−11 dB/m), as well as high OAM purity (larger than 98.295%). Therefore, the structure has immense potential in optical communication. [ABSTRACT FROM AUTHOR]

In recent years, solar energy has become popular because of its clean and renewable properties. Meanwhile, two-dimensional materials have become a new favorite in scientific research due to their unique physicochemical properties. Among them, monolayer molybdenum disulfide (MoS2), as an outstanding representative of transition metal sulfides, is a hot research topic after graphene. Therefore, we have conducted an in-depth theoretical study and design simulation using the finite-difference method in time domain (FDTD) for a solar absorber based on the two-dimensional material MoS2. In this paper, a broadband solar absorber and thermal emitter based on a single layer of molybdenum disulfide is designed. It is shown that the broadband absorption of the absorber is mainly due to the propagating plasma resonance on the metal surface of the patterned layer and the localized surface plasma resonance excited in the adjacent patterned air cavity. The research results show that the designed structure boasts an exceptional broadband performance, achieving an ultra-wide spectral range spanning 2040 nm, with an overall absorption efficiency exceeding 90%. Notably, it maintains an average absorption rate of 94.61% across its spectrum, and in a narrow bandwidth centered at 303 nm, it demonstrates a near-unity absorption rate, surpassing 99%, underscoring its remarkable absorptive capabilities. The weighted average absorption rate of the whole wavelength range (280 nm–2500 nm) at AM1.5 is above 95.03%, and even at the extreme temperature of up to 1500 K, its heat radiation efficiency is high. Furthermore, the solar absorber in question exhibits polarization insensitivity, ensuring its performance is not influenced by the orientation of incident light. These advantages can enable our absorber to be widely used in solar thermal photovoltaics and other fields and provide new ideas for broadband absorbers based on two-dimensional materials. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a dual-band metamaterial perfect absorber based on a Ag-dielectric-Ag multilayer nanostructure. The structure of top metal film covers nanoring grooves array. A dielectric layer has a function of confining electromagnetic fields. Theoretical analysis shows that two absorption peaks (1059 nm and 1304 nm) with the absorption of 99.2% and 99.9% have been achieved, respectively. The physical origin of perfect absorption peaks are related to the Fabry-Perot resonance effect and localized surface plasmon resonance (LSPR) of the nanoring grooves. Its perfect absorption and resonance wavelength can be well regulated by adjusting the relevant structural parameters. Additionally, the absorber demonstrates good operation angle-polarization-tolerance at wide incident angles (0–60°). We believe that our design has a promising application in plasmon-enhanced photovoltaic, optical absorption switching, and modulator optical communications in the infrared regime. [ABSTRACT FROM AUTHOR]

This paper presents a novel graphene-based proportional structure for a tunable wideband absorber in the terahertz (THz) frequency range. In order to achieve the ideal design structure, we make the distance between the top graphene structure and the periodic edge remains proportional, enabling excellent absorption with an absorption rate exceeding 90 % within the frequency range of 3.1–6.97 (3.87)THz. Notably, a perfect absorption is achieved at f = 6.5 THz. At f = 4.2 THz, the absorption rate is close to 97 %, and at f = 5.2 THz, the absorption rate is about 91 %. The average absorption rate is 94.6 % in the range of 3.1–6.97 THz. The absorber's impedance is calculated to demonstrate its favorable absorption band. Furthermore, an analysis of the electric field within the absorber reveals the coupling effect of strong electric fields between different regions, leading to the overlapping of absorption peaks and the formation of a wideband response. This allows us to choose regions to combine according to the needs of the application. By adjusting the parameters of the absorber, it exhibits coordinated performance and manufacturing tolerance. Additionally, the absorber shows a certain degree of tolerance to the incident angle of electromagnetic waves. These findings highlight the potential applications of this absorber in optoelectronic devices, THz detection, and stealth technology. [Display omitted] • Through CST calculation, this model can achieve bandwidth absorption in the terahertz frequency band. • Designed through a single layer of graphene with strong adjustability. • The electric field distribution and absorption principle were investigated by structure decomposition. • The model has a wide absorption rate and can achieve THz stealth. [ABSTRACT FROM AUTHOR]

The optical properties and the local electromagnetic field enhancement of a compound structure with rectangular nanohole arrays in Au-interlayer-Au multilayer films are numerically studied using finite-difference time domain method. We investigated some of structure parameters that influence the optical properties of the compound nanostructure. Adjustment of the length of rectangular nanoholes (L), the polarization direction (θ), the thickness of interlayer (SiO, H), and the materials in the interlayer can change the absorption intensity and the resonance peaks. An interlayer is located between the double Au films (Au-interlayer-Au multilayer films) with the function of confining local electromagnetic field. The simulation of the electromagnetic field distribution shows that the location of the local electromagnetic field enhancement can specify the different resonance patterns. The proposed compound nanostructure will be promising for application in portable nanoplasmonic multisensing and imaging. [ABSTRACT FROM AUTHOR]

We have reported on the synthesis of ordered hexagonal Au nanoparticle (NPs) arrays by anodic alumina oxide templates (AAO)-assisted thermal treatment. This simple process has led to the formation of an ordered hexagonal array of Au NPs on the surface of AAO. SERS properties of the ordered hexagonal Au NPs could be obtained by varying the size of Au NPs. Compared with the Au thin film on AAO, the SERS intensity of rhodamine adsorbed on the ordered hexagonal Au NPs was about 1000 times stronger. And the hexagonal Au NPs array films have had stronger Raman-enhanced signal compared to the disorder Au NPs films. Simulations according to the three-dimensional finite-difference time domain (3D-FDTD) have displayed that these electric field enhancements of the ordered hexagonal Au NPs are strongly dependent on the gap distance. Plasmonic ordered hexagonal Au NPs could provide us new platforms to realize novel optoelectronic devices. [ABSTRACT FROM AUTHOR]

In this study, high quality and yield Ag nanowires (NWs) have been fabricated via a microwave-assisted polyol technique by adding sodium bromide (NaBr) into the solution. In our experiments, the Ag NWs with diameters from 45 to 200 nm are rapidly prepared in 3 min. The fabrication parameters, such as the powers of microwave, concentration of NaBr solution, molar ratio of PVP:AgNO 3 , and the time of microwave, have been investigated in detail. Ag NWs with adjustable diameters can be obtained by adjusting the microwave powers and the NaBr solution concentration. The different microwave powers can provide different reaction energy, result in different reaction rate during the ultrafast nucleation and growth process. The Br − ions can enhance oxidative etching effect and decrease the diameters of the Ag NWs. Our works provide a new and facile approach for the large scale synthesis of Ag NWs with adjustable diameters by simply adjusting microwave powers and the NaBr solution concentration. [ABSTRACT FROM AUTHOR]

We report a simple magnetron sputtering method to fabricate large-scale vertically aligned ZnO@Ag nanorods (NRs) arrays using aligned ZnO-NRs arrays as a template. Via changing the thickness of Ag film, the density of Ag nanoparticles (NPs) on the surface of ZnO-NRs arrays can be readily tuned. Due to synergistic and charge transfer (CT) effect of the adjacent Ag NPs and ZnO-NRs, the optimized ZnO@Ag-NRs arrays employing Ag film with 15 nm thickness show the best surface-enhanced Raman scattering (SERS) for 4-aminothiophenol (4-ATP). The considerable SERS enhancement of the 4-ATP is ascribed to the CT between the 4-ATP and Ag NPs through the ZnO-NRs. With the help of the valence band of ZnO, the photo-induced electrons from the Ag NPs can be transferred to the lowest unfilled orbital (LUMO) of 4-ATP, forming the so-called “donor-bridge-acceptor” system. The present research is not only beneficial to the development of ZnO-NRs arrays as a nontoxic, biocompatible, highly SERS active substrate, but also helpful to study the CT behavior between Ag and ZnO for optoelectronic chemistry. [ABSTRACT FROM AUTHOR]

Simulation based on the finite-difference time-domain (FDTD) has been performed, and theoretical models comprising concentric Ag nanoring-nanodisk of different parameters have been constructed to research their plasmon properties. According to unique electronic properties of concentric nanoring-nanodisk, abundant plasmon properties could be obtained at their interfaces, including dipole, quadrupole, and octupole plasmon resonance modes. Complex field distributions which are induced by concentric nanoring-nanodisk support the possibility to create dark resonance mode. This can lead to Fano-like resonance combining with bright resonance mode by predominantly dipole resonance. A concentric nanoring-nanodisk system has been proved to support Fano-like resonance without symmetry breaking. At the frequency of the Fano resonance, strong localized optical fields can be obtained. Narrow spectral features with high local fields of Fano resonances make it possible to achieve many applications based on surface plasmon property. [ABSTRACT FROM AUTHOR]

The optical properties and the local electromagnetic field enhancement of a multilayer structure with square lattice nanohole arrays in Au-SiO 2 -Au multilayer films are numerically studied using finite-difference time domain method. Simulation results demonstrate that the multiple surface plasmons (SP) resonances consist of SP on the air/Au interface, SiO 2 /Au interfaces (the middle layers), Au/SiO 2 interface (the lower layer) and coupling modes on the Au film and Au film. We investigated some of structure parameters that influence the SP resonances of the multilayer nanostructure. Adjustment of the thickness of SiO 2 film (H 2 ), the diameter (R) of circular nanoholes, the periods (C) of square lattice and the thickness of Au film (H 1 ) could change the absorption intensity and the SP resonances. The simulation of the electromagnetic field distributions shows that the location of the local electromagnetic field enhancement can specify the different SP resonances patterns. Dipole, quadrupole, and twelve-pole SP resonances modes can be found in the multilayer nanostructure. These studies are important for applications using multiple SP resonances. [ABSTRACT FROM AUTHOR]

Well-aligned ZnO nanorod arrays have been prepared by using seed-assisted hydrothermal method, in which the c-axis oriented ZnO films prepared by a soft-chemical were used as the seed layers on quartz glass. The epitaxial growth mechanisms and corresponding morphology effect of samples are discussed. The results show that the morphology of ZnO nanorod arrays is closely related to the hydrothermal temperature, pH value and initial concentration of Zn source in precursor solution. The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), Raman spectroscopy, photoluminescence (PL) spectra and UV–vis spectra. The well-aligned ZnO nanorod arrays exhibit improved photocatalytic degradation with Rhodamine 6G (R6G) solution under UV radiation, according with the UV–vis spectra investigation and photocatalytic improvement speculation. Noteworthy, the photocatalytic properties of well-aligned ZnO nanorod arrays have obviously improved comparing with other ZnO samples without proper alignment. The oxygen vacancies suppressed recombination process of photon induced electrons and holes, as the oxygen vacancy trapped the charge carriers. [ABSTRACT FROM AUTHOR]

Here, we provide a simulation based on finite-difference time-domain (FDTD) way of the properties of surface plasmons on Ag nanoring and study their electric field distribution in order to identify different multiple surface plasmon resonances. We can obtain the symmetric field distribution that parallels to the orientation of direction of incident light. We find their propagation can be controlled. And we discuss some of the parameters that influence the optical response of the Ag nanoring. Adjustment of nanoring radius (inner radius and outer radius) and height can change the absorption intensity and the resonance peaks. The simulation of the field distribution also displays that the location of the field enhancement is specified by the different resonance patterns. Dipole, quadrupole, and octupole plasmon resonance modes can be found in the Ag nanoring at resonance wavelength. This is an important step toward a thorough understanding of plasmon resonance in Ag nanorings. [ABSTRACT FROM AUTHOR]

We reported a simple hydrothermal method to fabricate Au nanoparticles-decorated ZnO nanorods (ZnO-NRs) using aligned ZnO-NRs arrays as a template. Via changing the concentration of HAuCl aqueous solution, the size and density of Au nanoparticles (NPs) on the surface of ZnO-NRs could be readily tuned. The photoluminescence of Au-NPs decorated ZnO-NRs were investigated, in order to optimize the configuration of the Au-NPs decorated ZnO-NRs system realizing the maximum band emission. Due to a synergistic effect of the adjacent Au NPs and ZnO-NRs and efficiently coupled localized surface plasmon resonance (SPR) excitation, an optimized sample employing Au NPs with 15-nm size showed best catalytic efficiency. We have proposed a mechanism that is the electron transfer from surface-plasmon-stimulated \Au NPs to the conduction band of ZnO-NRs. These results demonstrate that Au NPs can significantly enhance the charge separation by extracting electrons from the photoexcited ZnO and consequently improve the photocatalytic activity of the composites. [ABSTRACT FROM AUTHOR]

A thermally tunable terahertz window based on the combination of a metamaterial and the phase change material VO2 is proposed. The window is composed of two vanadium oxide films with a SiO2 layer sandwiched between them. The thermochromic phase change properties of VO2 are the key to the functionality of the window. By controlling the temperature around the room temperature of 300 K, our material can be used as a smart window and it is able to regulate both the absorption and transmission of external terahertz waves in response to changes in temperature. The absorbance can be regulated by more than 90% and the transmittance by more than 80%. The switching characteristics of the window are explained by the insulator–metal transition that vanadium oxide undergoes during the heating process, while localized surface plasmon resonance explains the perfect absorption. In addition, the designed window is not only insensitive to polarised waves, but is thermally flexible and maintains excellent performance over a wide angular range of 0° to 40°. This design will have significant potential for applications in stealth technologies, thermal sensing and switching, and terahertz energy harvesting. [ABSTRACT FROM AUTHOR]

Abstract: A simple and reproducible way was explored to synthesize quasi-spherical gold particles with different size distributions in water by rapidly adding a mixture solution of HAuCl4, sodium citrate, and a trace amount of silver nitrate. By careful tuning of the reaction parameters, mono-disperse gold particles with the diameter of 5–220nm can be obtained controllably. The particle size of 130nm for the particles film showed the highest SERS activity with the 632.8nm excitation. The theoretical calculations of the UV–vis extinction spectra can be directly compared with experiments by using the discrete-dipole approximation (DDA). Control of nanostructure shape allows optimization of plasmon resonance for molecular detection and spectroscopy. [Copyright &y& Elsevier]

We investigate the surface-enhanced Raman spectroscopy of Ag nanorings antenna in both experiment and simulation. Self-organized Ag nanorings antenna were formed on quartz glass wafers by a simple chemistry reaction without any template. The three-dimensional finite-difference time-domain simulation calculations indicate that the electric field enhancement of Ag nanoring antenna is strongly dependent on the gap distance. A very strong surface plasmon coupling in the gap region of Ag nanoring antenna is observed, whose field intensity is enhanced four times compared to that for Ag nanodomes antenna with the same gap distance. Surface-enhanced Raman scattering (SERS) measurements have shown that the SERS intensity acquired from the Ag nanoring antenna is about 16 times stronger than that obtained from Ag nanodomes antenna. These results pave the way to design plasmonic nanostructures for practical applications that require coupled metallic nanoparticles with enhanced electric fields. [ABSTRACT FROM AUTHOR]

Silver nanosheets (NSs) have been synthesized by an electroless plating approach using a complexation mechanism of triethanolamine (TEA) and Ag to reduce the oxidation-reduction potential difference and slow down the deposition speed of Ag on quartz glass substrates. The synthesized Ag NSs with 500 nm in edge length and 30 nm in thickness stand on the substrates and are dispersed uniformly. The formation mechanism of Ag NSs is proposed. The formation of Ag NSs is attributed to the molar ratio of AgNO to TEA, the concentration of AgNO and the influence of reaction temperature. This study is important in vertical immobilization Ag NSs on solid substrates, which could provide substrates for catalysis or surface-enhanced Raman scattering. [ABSTRACT FROM AUTHOR]

Recently, the keen demand for multi-band perfect absorbers in spectroscopy, infrared detection, and other fields has intensified. To meet the energy demand, here we propose an Ag-Dielectric-Ag multilayer triple-band perfect absorber exhibiting perfectly resonance absorption in the near-infrared region. And the numerical calculations indicate that we obtain three resonance absorption peaks (908 nm, 1085 nm, and 1216 nm) with the maximal absorption of 99.09%, 99.84%, and 99.21%, respectively. Based on this, we propose that the physical formation mechanism of three resonance peaks are the Fabry-Pérot resonance effect and Localized surface plasmon polaritons resonance. Theoretically combined with the electromagnetic coupling theory to explain how the resonance-enhanced absorption. At the same time, by the comparison with the complementary structure, it is theoretically proposed that the MIM structure has a Fabry-Pérot resonance effect in the near-infrared region and then computationally verified the Fabry-Pérot formula. Furthermore, we can adjust the amplitude and wavelength of resonance peaks by modifying the geometry unit cell. And our proposed triple-band perfect absorber has some excellent properties, such as high absorptivity, multi-band, tunable, suitability for wide incidence angles, excellent angle tolerance, polarization tolerance, etc. In addition, our TBPA has a simple structure, which simplifies the processing technology and economically saves processing costs. Furthermore, the following simulations investigate the absorption spectrum of our TBPA exhibit property changes significantly as the environment changes. So we can calculate the sensitivity of three modes (sorted by resonance wavelength from short to long) is S1 = 70.09 nm/RIU, S2 = 208.26 nm/RIU, and S3 = 50.06 nm/RIU, respectively. Therefore, we believe that this triple-band perfect absorber can capture maximize optical energy and apply it in devices and materials for light conversions, like plasmon-enhanced photovoltaics, optical absorption switching, and modulator-optical communications. We propose an Ag-Dielectric-Ag multilayer triple-band perfect absorber with the periodic combination of the top composite silver rectangular loops, intermediate dielectric layer, lower silver layer, and bottom silicon layer, which exhibit three resonance absorption peaks (908 nm, 1085 nm, and 1216 nm) with the maximal absorption of 99.09%, 99.84%, and 99.21%, respectively, in the near-infrared region. We find that the maximal absorption enhanced significantly when compared to the absorber having dielectric-Ag-dielectric multilayers (below 10%) or having only the silver square loops (90.61% and 96.53%) or only the silver cuboids (98.53%). Our proposed TBPA has a higher efficiency compared with similar TBPA previously of three resonance peaks. And the highest sensitivities of the three modes reach 70.09 nm/RIU, 208.26 nm/RIU, and 50.06 nm/RIU. The highest sensitivity is high up to 208.26 nm/RIU, which possesses an immense practical value in the field of RI sensors. [Display omitted] • The absorption of the TBPA with three resonance absorption peaks has reached to 99.09%, 99.84%, and 99.21%. • The Fabry-Perot formula was theoretically proposed to verify a Fabry-Perot resonance effect. • Three high sensitivity of different resonance modes have reached 70.09 nm/RIU, 208.26 nm/RIU, and 50.06 nm/RIU, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Silver spongelike networks were synthesized from an alkaline pH solution of silver nitrate and glucose under solvothermal conditions. The products were characterized by X-ray powder diffraction, UV–visible spectroscopy, transmission electron microscopy, scanning electron microscopy and selected area electron diffraction. These Ag nanoparticles (NPs) appear to undergo sequentially linear aggregation and welding initially, and then, they randomly cross link into self-supporting, three-dimensional (3D) networks with time. The carboxylate groups, generated by glucose oxidation, interacted with the Ag nanostructures, resulting in formation of silver spongelike networks having very uniform wire diameters distributions (about 20 nm in diameter). A new plasmon band was observed in the longer-wavelengths region (565–912 nm) of the conventional transverse plasmon resonance band at 430 nm. In principle, this one-step, template-free approach can also be extended to large-scale 3D organizations of other transition/noble metal NPs. [Copyright &y& Elsevier]

Silver nanoplates were prepared in a dual reduction system with NaBH and sodium citrate both as reducing agents. And then the as-prepared nanoplates could be growing up through multistage growth methodology. The average edge length of Ag nanoplates can be tailored from 40 nm to 260 nm without changing their shape, crystallinity, and the average thickness. Furthermore, the effectiveness of these silver nanoplates as substrates prepared by the silanization self-assembly method toward surface-enhanced Raman scattering (SERS) detection was evaluated by using 4-aminothiophenol (4-ATP) and rhodamine 6G (R6G) as probe molecules. It was found that the enhancement ability of the silver nanoplates film is remarkable lower than that of the spherical silver nanoparticle film. The reason is attributed to the electromagnetic mechanism and chemical mechanism. This work will be of great significance in understanding the SERS enhancement mechanism and in the fabrication of nanoparticle films for biosensing. [ABSTRACT FROM AUTHOR]

Abstract: Dendritic Ag–Pd bimetallic nanostructures have been synthesized on the surface of Cu foil via a multi-stage galvanic replacement reaction (MGRR) of Ag dendrites in a Na2PdCl4 solution. After five stages of replacement reaction, one obtained structures with protruding Ag–Pd flakes; these will mature into many porous structures with a few Ag atoms that are left over dendrites. The dendritic Ag–Pd bimetallic nanostructures were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS). The morphology of the products strongly depended on the stage of galvanic replacement reaction and reaction temperature. The morphology and composition-dependent surface-enhanced Raman scattering (SERS) of the as-synthesized Ag–Pd bimetallic nanostructures were investigated. The effectiveness of these dendritic Ag–Pd bimetallic nanostructures on the surface of Cu foil as substrates toward SERS detection was evaluated by using rhodamine 6G (R6G) as a probe molecule. The results indicate that as-synthesized dendritic Ag–Pd bimetallic nanostructures are good candidates for SERS spectroscopy. [Copyright &y& Elsevier]

Abstract: Dendritic Ag/Au bimetallic nanostructures have been synthesized via a multi-stage galvanic replacement reaction of Ag dendrites in a chlorauric acid (HAuCl4) solution at room temperature. After five stages of replacement reaction, one obtains structures with protruding nanocubes; these will mature into many porous structures with a few Ag atoms that are left over dendrites. The morphological and compositional changes which evolved with reaction stages were analyzed by using scanning electron microscopy, transmission electron microscopy, UV–visible spectroscopy, selected area electron diffraction and energy-dispersive X-ray spectrometry. The replacement of Ag with Au was confirmed. A formation mechanism involving the original development of Ag dendrites into porous structures with the growth of Au nanocubes on this underlying structure as the number of reaction stages is proposed. This was confirmed by surface-enhanced Raman scattering (SERS). The dendritic Ag/Au bimetallic nanostructures could be used as efficient SERS active substrates. It was found that the SERS enhancement ability was dependent on the stage of galvanic replacement reaction. [Copyright &y& Elsevier]

Abstract: Silver nanoplates, with average size tunable from 50 to 500nm, have been synthesized via a simple room-temperature tannic acid (TA) solution-phase chemical reduction method. The synthesis was a seedless process in which tannic acid was used as a reducing as well as a capping agent, and did not need any other surfactant or capping agent to direct the anisotropic growth of the silver nanoparticles. The morphology of silver nanoplates has been confirmed by transmission electron microscopy, the growth process of nanoplates has been studied by UV/vis spectroscopy. Control experiments have been explored for a more thorough understanding of the growth mechanism. It was found that both the concentrations of TA and the pH of solution were the key elements to control the morphology silver nanoplates. The optical in-plane dipole plasmon resonance bands of these silver plates could be tuned from 520 to 1100nm. [Copyright &y& Elsevier]

Abstract: In this paper, an Au/Ag bimetallic hollow nanostructure was obtained by using SiO2 nanospheres as sacrificial templates. The nanostructure was fabricated via a three steps method. SiO2@Au nanospheres were first synthesized by the layer-by-layer technique, and then they were coated with a layer of Ag particles, finally, the Au/Ag bimetallic hollow nanospheres were obtained by dissolution of the SiO2 core by exposure in HF solution. Several characterizations, such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and UV visible absorption spectroscopy were used to investigate the prepared nanostructures. The effectiveness of these Au/Ag bimetallic hollow nanospheres as substrates toward surface-enhanced Raman scattering (SERS) detection was evaluated by using rhodamine 6G (R6G) as a probe molecule. We show that such Au/Ag bimetallic hollow nanospheres structure films which consisting of larger interconnected aggregates are highly desirable as SERS substrates in terms of high Raman intensity enhancement. The Au/Ag bimetallic hollow nanostructured aggregate, interconnected nanostructured aggregate and nanoscale roughness are important factors responsible for this large SERS enhancement ability. [Copyright &y& Elsevier]

Accurate description of the aerodynamic and aerothermal environment is crucial to the integrated design and optimization for high performance hypersonic vehicles. In the simulation of aerothermal environment, the effect of viscosity is crucial. The turbulence modeling remains a major source of uncertainty in the computational prediction of aerodynamic forces and heating. In this paper, three turbulent models were studied: the one-equation eddy viscosity transport model of Spalart-Allmaras, the Wilcox k-ω model and the Menter SST model. For the k-ω model and SST model, the compressibility correction, press dilatation and low Reynolds number correction were considered. The influence of these corrections for flow properties were discussed by comparing with the results without corrections. In this paper the emphasis is on the assessment and evaluation of the turbulence models in prediction of heat transfer as applied to a range of hypersonic flows with comparison to experimental data. This will enable establishing factor of safety for the design of thermal protection systems of hypersonic vehicle. [ABSTRACT FROM AUTHOR]

How to facilitate photogenerated-carrier separation is an important step in developing excellent semiconductor photocatalysts for environmental pollutant removal. Herein, Ag2MoO4 (AMO) nanoparticles were assembled onto the surface of BiOBr (BOB) nanosheets to construct a highly efficient Z-scheme AMO/BOB heterojunction photocatalyst. Several analytical techniques were used to elucidate the characteristics and photocatalytic mechanism of the AMO/BOB heterojunction. Photodegradation experiments for removing methylene blue under simulated-sunlight irradiation reveal that a 20%AMO/BOB heterojunction exhibits excellent photodegradation activity with η(30 min) = 93.8% and kapp = 0.08638 min−1, which were greater by 4.5 and 5.6 times in comparison with that of pure BOB and AMO, respectively. Based on the experimental and density functional theory (DFT) calculation results, it is proposed that the Z-scheme carrier transfer/separation mechanism dominates the enhanced photodegradation performance of the composite photocatalysts. Additionally, the potential application of AMO/BOB photocatalysts in degrading various organic pollutants (including organic dyes, antibiotics and other serious organic pollutants) was also investigated. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel tunable THZ absorber consisting of a patterned graphene layer and a metal plate separated by a vanadium dioxide dielectric layer. The absorbent has a simple structure, is easy to make graphene patterns, and has a dual regulatory function. The ability to double regulate comes from the fact that the state of vanadium dioxide changes with the temperature between the insulating phase and the metal phase, resulting in a change in its conductivity. When vanadium dioxide is in the insulating phase, the total reflection characteristics of the absorber are >7 THz, and when vanadium dioxide is in the metallic phase, the absorber achieves near-perfect absorption in the ultra-wideband range of 3 THz to 12.4 THz (9.4 THz). Local surface plasmon resonance explains the perfect absorption. Compared with previous absorbers, our proposed absorbers are not only simple in structure, the graphene pattern is also easy to process, but also have double adjustment and perfect absorption in the ultra-wideband range, are not sensitive to polarized light, and have large tolerances for the Angle of incident. The further development and enrichment of terahertz metamaterials and metasurface devices will also have beneficial implications for terahertz wave applications in sensing, communications, and radar. Due to their significant application value in stealth, detection, and communication, metamaterial absorbers have become a research hotspot in the field of metamaterials. [Display omitted] • The absorber can realize ultra-wideband absorption from terahertz band to near infrared band. • This device achieves dual control by changing temperature and Fermi level. [ABSTRACT FROM AUTHOR]

Terahertz devices play an irreplaceable role in the development of terahertz technology. However, at present, it is difficult for most natural materials to respond in the terahertz band, making the devices made of them perform poorly. In order to realize the diversity and tunability of device functions, we designed a terahertz metamaterial device composed of the thermally-induced phase change material VO2. The device structure is composed of a Au bottom layer, a SiO2 dielectric layer and a VO2 top layer. Through software simulation, we found that when T = 313 K, the device has complete reflection ability in the whole terahertz band. When T = 342 K, the average absorptivity is above 95% in the ultra-wide band range of 4.71–9.41 THz, and the absorptivity reaches an amazing 0.99999 at 6.31 THz. Thus, the maximum thermal modulation range of the device is 0.001–0.99999. The Bruggeman effective medium theory clarifies the phase transition characteristics of vanadium dioxide. The Drude model establishes the functional relationship between the conductivity of vanadium dioxide and temperature. The basic principle of high absorption was described using the impedance matching theory. We also drew the electric field intensity diagram during the temperature rise of the device to further confirm the reason for the change in the device performance. In addition, the influence of the absence of different structural layers on the absorptivity was simulated, which reflected the role of each layer structure more intuitively. We also explored the influence of the geometric size of the device on the absorptivity, which provided a certain reference value for practical application. In short, we have designed a tunable terahertz device with simple structure, high absorptivity, and wide absorption bandwidth, which can be used in the fields of energy collection, electromagnetic stealth, and modulation. [ABSTRACT FROM AUTHOR]

Metamaterial absorbers show great potential in many scientific and technological applications by virtue of their sub-wavelength and easy-to-adjust structure, with bandwidth as an important standard to measure the performance of the absorbers. In this study, our team designed a new broadband absorber, which consists of an indium arsenide (InAs) disk at the top, a zinc selenide (ZnSe)-chromium (Cr) stacked disk in the middle and a metal film at the bottom. Simulation results show that the absorber has remarkable absorptivity properties in the mid-long infrared band. In a wavelength range of 5.71–16.01 μm, the average absorptivity is higher than 90%. In the band of 5.86–15.49 μm, the absorptivity is higher than 95%. By simulating the electromagnetic field diagram at each resonant frequency, the reason for high broadband absorptivity is obtained. We also constructed Poynting vector diagrams to further elucidate this phenomenon. Next, we analyzed the influence of different materials and structural parameters on absorptivity properties and tested spectral response at different polarization angles and oblique incidence of the light source in the TM and TE modes. When the source is normally incident, the absorber shows polarization insensitivity. When the angle is 40°, absorptivity is still high, indicating that the absorber also possesses angle insensitivity. The broadband absorber proposed by us has good prospects in infrared detection and thermal radiators. [ABSTRACT FROM AUTHOR]

In this paper, we propose a multiband adjustable metamaterial absorption device based on a Dirac semimetal (BDS) AlCuFe and a thermally controlled phase-change material VO2. The absorption device has an axially symmetric structure, resulting in polarization-independent characteristics, and when VO2 is in a high-temperature metal state, ultra-high absorption rates and sensitives at frequencies of M1 = 2.89 THz, M2 = 7.53 THz, M3 = 7.97 THz, and M4 = 9.02 THz are achieved. Using a parameter inversion method, we calculated the impedance of the absorber, proving that it achieves impedance matching and produces perfect absorption in the resonance region. Additionally, we changed the physical and chemical parameters of the absorption device, demonstrating the device's excellent tunability and manufacturing tolerance. Furthermore, by lowering the temperature of VO2 to that of a low dielectric state, additional resonant peaks with ultra-high absorption rates at frequencies M5 = 5.62 THz, M6 = 7.16 THz, M7 = 7.64 THz, and M8 = 8.80 THz were obtained, broadening the absorption band of the device. Lastly, we investigated the detection sensitivity of the device by changing the external refractive index, resulting in a maximum sensitivity of 2229 GHz RIU−1. To sum up, the absorption device has great application potential in the fields of communication, sensing, temperature detection and photoelectric instruments. [ABSTRACT FROM AUTHOR]

In recent years, absorbers related to metamaterials have been heavily investigated. In particular, VO2 materials have received focused attention, and a large number of researchers have aimed at multilayer structures. This paper presents a new concept of a three-layer simple structure with VO2 as the base, silicon dioxide as the dielectric layer, and graphene as the top layer. When VO2 is in the insulated state, the absorber is in the closed state, Δf = 1.18 THz (absorption greater than 0.9); when VO2 is in the metallic state, the absorber is open, Δf = 4.4 THz (absorption greater than 0.9), with ultra-broadband absorption. As a result of the absorption mode conversion, a phenomenon occurs with this absorber, with total transmission and total reflection occurring at 2.4 THz (A = 99.45% or 0.29%) and 6.5 THz (A = 90% or 0.24%) for different modes. Due to this absorption property, the absorber is able to achieve full-transmission and full-absorption transitions at specific frequencies. The device has great potential for applications in terahertz absorption, terahertz switching, and terahertz modulation. [ABSTRACT FROM AUTHOR]

This paper proposes a dual-frequency tunable ideal visible light metamaterial absorber based on the sub-wavelength range, which achieves perfect absorption in the visible light band. The absorber consists of an Au reflector and a nodal (SiO 2) layer, and a top Au absorber layer. The absorption structure on the top of the absorber adopts the style of ancient Chinese coins and forms a square arrays structure. As a result, the absorber's two absorption peaks are perfect absorption peaks, and the absorption rate can reach 99.9%. In addition, we also researched the influence of adjusting the absorber's geometric parameters on the absorber, and analyzed the absorption mechanism under different circumstances. Through research, it can be known that the absorber has near-perfect dual-band absorption characteristics that do not depend on polarization angle and incident angle insensitivity. Therefore, the absorber designed by us will have a broad application prospect in the filter, solar cell, and so on. We design a tunable metamaterial absorber based on sub wavelength range. By adjusting the structural parameters of the absorber, it can achieve perfect absorption in the visible light band. It is insensitive to angle and polarization, and has a broad application prospect in filter, solar cell. Image 1 • By changing the structural parameters of the absorber, we can adjust the absorption spectra of the absorber. • Can be implemented within the scope of the visible dual band perfect absorption. • The absorber is insensitive to changes in the incidence angle. • The absorber is not sensitive to the change of polarization direction of incident light. [ABSTRACT FROM AUTHOR]

Morphology of photocatalyst has attracted many attentions due to its significant effect on photocatalytic properties. Herein, the effects of hydrothermal reaction conditions including time, temperature, and pH value on the morphology evolution as well as on the photocatalytic performance of SrMoO4 were investigated in detail. It was found that SrMoO4 had self‐assembled dual morphologies (spherical and dumbbell shape) under the specific reaction conditions with time=24 h, temperature=200 °C, and pH=6.13. In order to enhance its photocatalysis further, the silver nanoparticles (Ag‐NPs) were well‐dispersed uniform on the surface of as‐prepared samples to obtain Ag‐NPs/SrMoO4 composites by photoreduction method. It was determined that 3 %Ag‐NPs/SrMoO4 had the first‐class photocatalytic performance (η=83.7 %, kapp=0.05229 min‐1) for the photodegradation of MB dye, which is ∼2.52 times that of the bare SrMoO4 with dual morphology (η=51.9 %, kapp=0.02078 min−1) by comparison with the apparent first‐order reaction rate constants. The photocatalytic performance was promoted by high efficiency of photo‐induced carriers' separation based on the effect of Localized Surface Plasmon Resonance (LSPR) of well‐dispersed Ag‐NPs. [ABSTRACT FROM AUTHOR]

In the development of orbital angular momentum (OAM) mode division multiplexing, the capacity of optical fiber communication must be improved. However, owing to dispersion and confinement loss, many OAM modes do not propagate stably over a long distance in optical fibers. In this work, the effects of the size, number, shape, number of layers, and layer spacing of air holes in the cladding of the fiber on the dispersion and confinement loss are analyzed based on a simple structure. The trends are studied and summarized to facilitate the design of optical fibers to achieve stable transmission of OAM modes over a long distance. [ABSTRACT FROM AUTHOR]

In this paper, a broadband solar absorber is constructed and simulated based on the finite difference time domain method (FDTD). The modeled structure of the absorber consists of cyclic stacking of five absorber cells with different periods on refractory metal W, where a single absorber cell is composed of a three-layer SiO2-InAs-TiN square film. Due to the Fabry–Perot resonance and the surface plasmon resonance (SPR), an absorptivity greater than 90% within a bandwidth of 2599.5 nm was achieved for the absorber. Notably, one of these bands, 2001 nm, is a high-efficiency absorption with an absorption rate greater than 99%. The average absorption efficiency reaches 99.31% at an air mass of 1.5 (AM 1.5), and the thermal radiation efficiencies are 97.35% and 97.83% at 1000 K and 1200 K, respectively. At the same time, the structure of the absorber is also polarization-independent, and when the solar incidence angle is increased to 60°, it still achieves an average absorption of 90.83% over the entire wavelength band (280 nm to 3000 nm). The novelty of our work is to provide a design idea based on a unit structure with multiple cycles, which can effectively expand the absorption bandwidth of the absorber in the visible-near-infrared wavelengths. The excellent performances make the structure widely used in the field of solar energy absorption. [ABSTRACT FROM AUTHOR]

This paper proposes a hybrid microwave power receiving (MPR) metasurface array with efficient dual matching of surface impedance and phase gradient. The hybrid array comprises three components: a reflective phase gradient metasurface (R-PGM) array, a surface wave focusing array, and an energy harvesting port. The R-PGMs efficiently convert incident electromagnetic waves into surface waves. The surface wave focusing array then concentrates the energy onto the integrated harvesting port through dual matching of surface impedance and phase gradient. Connecting a rectifier circuit enables efficient microwave energy reception and RF-DC conversion, avoiding the need for multiple rectifiers or complex feeding networks in traditional MPR designs. Numerical analysis and experimental tests verify the superior performance of this hybrid array design in efficient microwave energy harvesting and RF-DC conversion, achieving 90.84% plane wave-to-surface wave conversion efficiency, 76.67% surface wave energy harvesting efficiency, and 49.28% overall RF-DC conversion efficiency. Across the wideband range of 5.6–6.0 GHz, the energy harvesting efficiency remains consistently high, demonstrating the superior characteristics and promising potential of this design in MPR device development. [ABSTRACT FROM AUTHOR]

This work proposes a colored intelligent thermal control emitter characterized by adjustable structural color development with a reflection spectrum in the visible light range and intelligent thermal control with temperature switching in the mid infrared wavelength band. In the beginning, we investigate an intelligent thermal control emitter based on a multilayer membrane formed by the phase change material vanadium dioxide, metal material Ag, and dielectric materials Ge and ZnS. By incorporating the thermochromic material vanadium dioxide, the structure exhibits a high emissivity of ε H = 0.85 in the range of 3–13 μm wavelength when in the high temperature metallic state, enabling efficient heat radiation. In the low temperature dielectric state, the structure only has a low emission capacity of ε L = 0.07, reducing energy loss. Our results demonstrate that the structure achieves excellent emission regulation ability (Δ ε = 0.78) through the thermal radiation modulation from high to low temperature, maintaining effective thermal control. Furthermore, the thermal control emitter exhibits selective emission of peak wavelength due to destructive interference and shows a certain independence on polarization and incidence angle. Additionally, the integration of structural color adjustment capability enhances the visual aesthetics of the human experience. The proposed colored intelligent thermal control structure has significant potential for development in aesthetic items such as colored architecture and energy-efficient materials. We propose a colored intelligent thermal control emitter characterized by adjustable structural color development with a reflection spectrum in the visible light range and intelligent thermal control with temperature switching in the mid infrared wavelength band. By incorporating the thermochromic material vanadium dioxide, our results demonstrate that the structure achieves excellent emission regulation ability (Δ ε = 0.78) through the thermal radiation modulation from high to low temperature, maintaining effective thermal control. Additionally, the integration of structural color adjustment capability enhances the visual aesthetics of the human experience. The proposed colored intelligent thermal control structure has significant potential for development in aesthetic items such as colored architecture and energy-efficient materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Utilizing the phase transition principle of VO2, this paper presents a tunable ultra-wideband terahertz perfect absorption device with simple structure and tunability. The proposed broadband terahertz perfect absorption device is a three-layer structure with a metal reflective layer, a silicon dioxide dielectric layer and a VO2 layer from bottom to top. It was found that the terahertz perfect absorption device's absorption could be dynamically adjusted from 1.2% to 99.9% when changing from an insulated to a metallic state. With the VO2 in the metallic state, the terahertz perfect absorption device has an absorption efficiency of more than 90% in 4.00 to 10.08 THz's ultra-broadband range and near-perfect absorption is achieved in the ranges of 4.71 THz to 5.16 THz and 7.74 THz to 8.06 THz. To explain the working principle of this terahertz perfect absorption device, this paper utilizes wave interference's principle, theory of impedance matching and electric field analysis. Compared to previously reported terahertz metamaterial devices, the vanadium dioxide device proposed in this paper is significantly optimized in terms of tunable range and absorption bandwidth. In addition, the terahertz perfect absorption device is polarization insensitive and maintains good absorptivity over a wide-angle incidence range. This tunable ultra-wideband terahertz perfect absorption device could have applications in the fields of modulation, stealth devices, and thermal emission devices. [ABSTRACT FROM AUTHOR]

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]

In this study, we combine the methods of magnetron sputtering, hydrothermal growth, and stepwise deposition to prepare novel ZnO@Ag3PO4 core-shell nanocomposite arrays structure. Through scanning electron microscope (SEM) topography test, energy dispersive spectrometer (EDS) element test and X-ray diffractometry (XRD) component test, we characterize the morphology, element distribution and structural characteristics of ZnO@Ag3PO4 core-shell nanocomposite arrays structure. At the same time, we test the samples for light reflectance, hydrophilicity and photoelectric performance. We find that after deposition of Ag3PO4 on ZnO nanorods, light reflectance decreases. As the time of depositions increases, light reflectance gradually decreases. After the deposition of Ag3PO4, the surface of the sample shows super hydrophilicity, which is beneficial for the photoelectric performance test. Through the optical transient response test, we find that the photo-generated current reaches a maximum when a small amount of Ag3PO4 is deposited. As the time of depositions of Ag3PO4 increases, the photogenerated current gradually decreases. Finally, we conducted an alternating current (AC) impedance test and also verified the correctness of the photocurrent test. Therefore, the structure is expected to be prepared into a photoanode for use in fields such as solar cells. [ABSTRACT FROM AUTHOR]

This study analyzed the solar absorption characteristics of Trapezoidal Pyramid ultra-thin GaAs solar cells (GTCs) using the finite difference time domain (FDTD) method. The study explored the influence of geometric parameters of trapezoidal pyramid structures (TPs) in GTCs, including different heights and up/down ratios, on the photoelectric characteristics of GTCs. Ultra-thin GaAs solar cells containing TPs exhibited an optical absorption rate exceeding 90 % under the AM1.5 solar spectrum (300–1100 nm), with an average of 95.55 %. The short-circuit current density (Jsc), open-circuit voltage (Voc), and maximum power (P max) were calculated using DEVICE software, and the geometric structure of GTCs was optimized based on the maximum value of Jsc. The electrical simulation results show that the maximum Jsc was 33.83mA/cm2. The Jsc of GTCs was 30.97 % higher than that of Ultra-thin GaAs solar cells without TPs (planar GACs), resulting in a PCE of 24.34 %. These findings demonstrate that the TPs array has a strong optical capture effect and highlight the significant potential of GTCs in solar absorption. This work provides valuable insights for the structural design of GaAs solar cells and suggests that further exploration will lead to even greater improvements in the PCE of GaAs solar cells. [ABSTRACT FROM AUTHOR]

We propose a structurally simple, innovative, and multifunctional mid-infrared broadband thermally tunable metamaterial absorption device. The absorption device consists of a three-layer structure, from bottom to top: Ti substrate, SiO2 dielectric layer, and patterned VO2 layer. Through temperature control, the average absorption intensity of the absorption device can vary between 0.08 and 0.94. The absorption device's absorption mechanism is rooted in the thermal phase-change characteristics exhibited by the topologically patterned VO2. When the temperature is below 340 K, VO2 is in a dielectric state, resulting in near-total reflection performance in the mid-infrared range. When the temperature is above 340 K, VO2 undergoes a dielectric-to-metal transition, enabling the absorption device to achieve an average absorption rate of 94.12% in the ultra-wideband range of 6.26 μm–20.96 μm in the mid-infrared. This absorption range completely covers the atmospheric window wavelengths of 8 μm–14 μm, demonstrating high practical value. We explain the working mechanism of the absorption device from the perspective of the electromagnetic field. Subsequently, we study the variations in the absorption curve of the absorption device at different temperatures of VO2 and use the changes in the electric field at the same wavelength under different temperatures to explain the variations in absorption. Compared to previous work, our structure has only three layers in a single unit, making it easy to process and produce. Additionally, the absorption device's operating bandwidth and average absorption rate in the mid-infrared range have been significantly improved. Furthermore, the absorption device exhibits substantial incident angle tolerance and polarization insensitivity. We believe that this design has broad application potential in future optothermal conversion, infrared stealth, and thermal radiation. [ABSTRACT FROM AUTHOR]

As graphene-related technology advances, the benefits of graphene metamaterials become more apparent. In this study, a surface-isolated exciton-based absorber is built by running relevant simulations on graphene, which can achieve more than 98% perfect absorption at multiple frequencies in the MWIR (MediumWavelength Infra-Red (MWIR) band as compared to the typical absorber. The absorber consists of three layers: the bottom layer is gold, the middle layer is dielectric, and the top layer is patterned with graphene. Tunability was achieved by electrically altering graphene's Fermi energy, hence the position of the absorption peak. The influence of graphene's relaxation time on the sensor is discussed. Due to the symmetry of its structure, different angles of light source incidence have little effect on the absorption rate, leading to polarization insensitivity, especially for TE waves, and this absorber has polarization insensitivity at ultra-wide-angle degrees. The sensor is characterized by its tunability, polarisation insensitivity, and high sensitivity, with a sensitivity of up to 21.60 THz/refractive index unit (RIU). This paper demonstrates the feasibility of the multi-frequency sensor and provides a theoretical basis for the realization of the multi-frequency sensor. This makes it possible to apply it to high-sensitivity sensors. [ABSTRACT FROM AUTHOR]

Tunable double plasmon-induced transparency (PIT) based on monolayer black phosphorus (BP) metasurface is numerically studied in this work. The proposed metasurface is composed of a middle BP square block and a BP strip. Destructive interference between two bright modes and one dark mode gives rise to the double PIT spectrum. The coupled mode theory (CMT) with fitted parameters is utilized to illustrate the physical mechanism of the double PIT spectrum. The effect of the carrier concentration and geometrical size on the PIT spectrum is studied. A multiple-frequency synchronous "on"-"off" modulator is realized at [ f 1 , f 2 , f 3 , f 4 , f 5 , f 6 ] = [ 6.41 , 7.14 , 7.59 , 8.51 , 9.42 , 10.53 ] THz ; a high modulation depth (MD = 26.39 dB) and a low insertion loss (IL = 1.17) are achieved. Moreover, we found the sensing properties of the structure were excellent with a maximum refractive index sensitivity of about 5.25 THz / RIU and a maximum figure of merit (FOM) up to 48.7. Therefore, the proposed structure has potential applications in multifrequency optical switches, terahertz sensors, modulators, and slow light devices. [ABSTRACT FROM AUTHOR]

Solar absorber is the key component to realize efficient utilization of solar energy. In this paper, only titanium nitride (TiN) is used to create a broadband, wide-angle, polarization insensitivity solar absorber. The average absorption of the absorber in the spectral range of 300-2500 nm is 91.3%. The distributions of electric and magnetic fields indicate that the strong absorption is caused by the coupling effect of surface plasmon resonance and guided mode resonance. Investigate the effects of the geometric parameters of the absorber on the spectral absorption performance. Moreover, we also discuss the absorption performance of the solar absorber at different incidence angles. It is demonstrated that even at a large incidence angle of 60°, the average spectral absorption can exceed more than 70%. The proposed solar energy absorber is also insensitive to polarization. The research results in this work could benefit the applications in solar thermophotovoltaic system. [ABSTRACT FROM AUTHOR]

A monolayer graphene metamaterial structure with a periodic pattern of transverse graphene strip and semi-enclosed graphene square ring is proposed. The dynamically tunable quadruple plasmon-induced transparency (PIT) effect is achieved in the terahertz band. The strong destructive interference between the bright mode and the dark mode, the electric field distributions of the composite graphene structures explain this quadruple-PIT phenomenon well. The results obtained by finite-difference time-domain (FDTD) simulation agree well with those calculated by the coupled mode theory (CMT). By modulating the Fermi level of graphene, two hexa-frequency asynchronous switches and two quadruple-frequency synchronous switches are realized, their maximum modulation depth is 99.9%, and its corresponding insertion loss and extinction ratio are 0.10 dB and 29.90 dB, respectively. These excellent performances exceed many similar graphene metamaterial structures. Therefore, our proposed quadruple-PIT graphene metamaterial structure has potential application value for the design of terahertz multi-channel switches. [ABSTRACT FROM AUTHOR]

We report a numerical study of an ideal PEDOT:PSS/c-Ge Hybrid Solar Cells with trapezoidal pyramids structure (As shown in Fig. (a)). By optimizing the design, the average absorption efficiency in the AM 1.5 spectrum within the wavelength ranged from 300 nm to 1500 nm has reached 93.8% (As shown in Fig. (b)). When the ratio of top to bottom of the trapezoidal pyramids is 1/16 (T/B = 1/4, h = 300 nm), the J sc is up to 43.47 mA/cm2 (As shown in Fig. (c)) and the maximum power is 7.9 mW/cm2 (As shown in Fig. (d)). • The optical absorption of trapezoid-pyramidal HSCs is above 90% in the range of sunlight. • The average absorption of trapezoid-pyramidal HSCs is 93.8% under AM 1.5 solar spectrum. • The short circuit density of trapezoid-pyramidal HSCs has reached to 43.47 mA/cm2. • The trapezoid pyramid has a good light capture effect. In this paper, we have utilized finite difference time domain (FDTD) method to investigate the solar energy absorption of hybrid solar cells (HSCs) with trapezoid-pyramidal structure (TPs) based PEDOT:PSS/c-Ge. We have changed some parameters of TPs (different heights and different ratios of top to bottom) to study its effects on the solar energy absorption for HSCs. The optimization of geometric parameters is based on the maximum solar energy absorption efficiency. The optical absorption of the HSCs with TPs is basically above 90% from ~300 nm to ~1300 nm and the average solar energy absorption is 93.8% under AM 1.5 solar spectrum (from 300 nm to 1500 nm). Simultaneously, we have calculated the short-circuit current density (J sc), open-circuit voltage (V oc), fill factor (FF), maximum power (P max) and photoelectric conversion efficiency (PCE) respectively through DEVICE software. The results of electrical simulation reveal that the maximum J sc is 43.47 mA/cm2, it is 45.73% higher than planar PEDOT:PSS/c-Ge HSCs. Moreover, to further explain the mechanism of solar energy absorption of HSCs with TPs, the logarithmic figures of electric field intensity for trapezoid-pyramidal PEDOT:PSS/c-Ge HSCs and planar PEDOT:PSS/c-Ge HSCs at different wavelengths are analyzed. The result shows that TPs array has shown excellent light-trapping effect. This work reveals the huge potential of c-Ge HSCs in solar absorption, and at the same time has certain guiding significance for the structural design of Ge SCs. It is believed that through further exploration, the conversion efficiency of c-Ge HSCs will be further improved. [ABSTRACT FROM AUTHOR]

In this work, we have adopted a coprecipitation method to synthesize BiOBr nanoplates with diameter of 150–450 nm and thickness of 40–80 nm, and then created Bi nanowires (diameter: 6 nm) on their surface through a NaBH4 reduction method. Evolution of Bi nanowires was systematically investigated by varying the concentration of NaBH4 solution and reaction time. It is demonstrated that with increasing the NaBH4 concentration (2 h reaction), Bi nanowires are gradually evolved from BiOBr crystals, and in particular treatment by 110 mM NaBH4 solution leads to the complete evolution of BiOBr nanoplates to Bi nanowires. At a low-concentration NaBH4 solution (30 mM), BiOBr crystals are partially reduced to Bi nanowires with increasing reaction time, and then the Bi nanowires are recrystallized into BiOBr nanowires/nanoparticles on the surface of BiOBr nanoplates. At a high-concentration NaBH4 solution (110 mM), BiOBr nanoplates are easily reduced to Bi nanowires with a short reaction time, and further prolonging the reaction time leads to the gradual transformation of Bi nanowires into Bi4O5Br2 nanoparticles/nanowires. Photocatalytic performances of the samples were evaluated by eliminating rhodamine B from aqueous solution under simulated sunlight illumination. It is demonstrated that the creation of Bi nanowires (an appropriate content) on the surface of BiOBr nanoplates can produce excellent Bi@BiOBr composite photocatalysts with enhanced photodegradation performances. The underlying enhanced photocatalytic mechanism was investigated and discussed. [ABSTRACT FROM AUTHOR]