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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, 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]

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]

Meta-optics has witnessed substantial advancements in recent years. Nevertheless, conventional forward design methodologies are encountering difficulties in the face of escalating demands for functional complexity. Inverse design aims to optimize meta-optical designs, but currently limited to expensive and powerful numerical solvers, it is mainly applied to simple functions devices, and is experimentally difficult to implement. In this paper, we put forth a generalized inverse design framework that facilitates the design of aperiodic complex functional meta-optics. The framework, consisting of a high-performance forward simulator model and a global optimization model, achieves system-level objective optimization. We design and implement a Long-Wave Infrared (LWIR) broadband achromatic metalens. The numerical findings indicate that the chromatic aberration is effectively rectified within the operational wavelength range of 8.6–11.4 μm, exhibiting a maximum focal length deviation percentage of 5.88 %. Moreover, the actual Numerical Aperture (NA) of the proposed LWIR broadband achromatic metalens attains a value of 0.54. The design of this broadband achromatic metalens is anticipated to have significant utility in the domain of LWIR integrated optical systems. [Display omitted] • We present a novel inverse design framework for meta-optics. • The proposed framework embeds neural network methods into traditional optimization algorithms. • We design and implement a long-wave infrared broadband achromatic metalens. [ABSTRACT FROM AUTHOR]

Electromagnetic wave absorbers with very long absorption spectra have become an important target for optoelectronic materials and technology. In this paper, we propose a titan-based resonator to achieve near-perfect wide spectrum absorption of solar radiation. In the whole spectrum of the study, the average absorption of the absorber is up to 93.17%. Using surface plasmon resonance, up to 1759 nm in the range of absorption over 90% in the absorption spectrum studied (166.8–1926.6 nm). Furthermore, the absorption spectrum of the absorber is not sensitive to polarization. Since the material constituting the absorber is a mainly refractory metal, it can work under a complex electromagnetic environment (solar radiation) and high-temperature conditions. Later, the influence of various parameters on the absorption spectrum and the mechanism of forming broadband absorption was explored. It is also found that other refractory metals similar to titanium have a good effect on the absorber with this structure. We report a numerical study of an ideal solar broadband absorber based on refractory titanium. By optimizing the design, the average solar absorption efficiency of the absorber in the studied wavelength range (100–2000 nm) is as high as 93.17%. Image 1 • The absorber is capable of obtaining ultra-wide spectrum absorption of solar energy. • The absorbency of the absorber can be adjusted by optimizing the structural parameters. • The absorber is insensitive to changes in the angle of incidence and polarization. • The absorber has certain versatility to other refractory materials. [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 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]

A five-band tunable ideal terahertz metamaterial absorber based on subwavelength range is proposed. It consists of a reflective layer, a dielectric layer, and an absorbing layer consisting of an internal closed square ring and an outer open square circle. We have found that the five absorption peaks can reach more than 97% on average. Meanwhile, in order to analyze the absorption mechanism, we studied the different structures and geometric parameters of the absorber and drew the electric field intensity diagram and surface current density diagram at different peaks. Moreover, we also studied the effect of similar opening structures based on this structure on absorption. Therefore, the designed absorber has good frequency selectivity and can be applied to terahertz imaging, detection, and so on. [ABSTRACT FROM AUTHOR]

[Display omitted] • Gallium is mainly hosted in Al-rich minerals. • Two types of magnetite have been identified. • Temperature may be the main reason for the variation of the Ga content in the different types of magnetite. The Dulong Sn polymetallic deposit is located in the SE Yunnan-West Guangxi ore province, and represents one of the three largest cassiterite-sulfide deposits in China. The deposit is a potential gallium (Ga) deposit in China with abundant tin and zinc resources. However, the occurrence of Ga in the deposit and the control on its mineralogy are still poorly understood. Here, we provide a detailed account of the gallium distribution in silicate, oxide, and sulfide minerals at Dulong, based on field geological and petrographic observations and geochemical analysis. Gallium is mainly hosted in Al-rich minerals, such as muscovite (avg. 139 ppm), biotite (avg. 86.8 ppm), and feldspar (avg. 21.3 ppm), in the ore-related granite. This distribution behavior of gallium is consistent with its predicted partitioning between the phenocrysts and melt. In the Sn ore, chlorite has high Ga content (avg. 104 ppm), probably caused by the gallium tends to form hydroxyl complexes. In contrast, pyroxene and sphalerite have low Ga content (avg. 1.24 and 1.50 ppm, respectively). Meanwhile, two types of magnetite (Mag-I and Mag-II) have been identified based on mineral paragenesis: Mag-I is mainly associated with sphalerite. It is porous, with the pores filled with Ga-rich aluminosilicates (e.g., chlorite), and has high Ga content (avg. of 18.3 ppm). Mag-II is mainly associated with sphalerite, pyrrhotite, and chalcopyrite, and has low Ga (avg. 1.34 ppm). The dissolution of Ga-rich aluminosilicates in magnetite likely provided gallium to magnetite, resulting in higher Ga content in Mag-I. The magnetite Ga content decrease with increasing distance from the mineralization center, and the magnetite mineralization temperature also shows a similar trend. This study confirms that the dominant substitution for Ga in muscovite is Ga3+ ↔ Al3+, and in magnetite it is Ga3+ ↔ Mn2+ + Me+ and Ga3+ ↔ Cu+ + Zn2+. Most of the Ga is hosted in chlorite and magnetite in the highly chloritized sulfide ore at Dulong, which is a critical factor that can significantly affect the estimation of economically recoverable by-product elements in the sulfide ore. [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]

In this paper, we present a dual-band metamaterial absorber for graphene surface plasmon resonance at terahertz frequency. We use the finite difference time domain (FDTD) method to study the absorption characteristics of the homocentric graphene ring and disk nanostructure. These simulation results show that the change of the geometrical parameters and the substrate thickness of the nanostructure can change the absorption characteristics and the emergence of dual-band absorption peaks. Moreover, we study the field distribution of nanodisks with different radius in detail. By changing the Fermi level of graphene, the wavelength of their absorption peaks can be adjusted flexibly. In addition, the proposed dual-band absorber also shows a good angle tolerance for both TE and TM polarizations. By calculation the surface-filled water (n = 1.332) and 25% aqueous glucose solution (n = 1.372) for the metamaterial absorber, the sensitivities of mode I and mode II are 5.0 μm/RIU and 15.0 μm/RIU. These research results will have broad application prospects for sensing and spatial light modulators. We present a dual-band metamaterial absorber for graphene surface plasmon resonance at terahertz frequency. We find the nanostructure absorption peak wavelength is flexible and adjustable by changing the graphene Fermi level E F. Image 1 • The absorption enhancement of the nanostructure can be achieved by changing the geometric parameters. • By changing the Fermi level, the absorption characteristics can be tuned. • As the relaxation time increases, the absorption maximum also increases, while the resonance peak wavelength remains unchanged. • For TM and TE polarizations, the absorbers are insensitive to the incident angle. [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 (MoS 2 ), 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 MoS 2 . 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.

In recent years, absorbers related to metamaterials have been heavily investigated. In particular, VO 2 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 VO 2 as the base, silicon dioxide as the dielectric layer, and graphene as the top layer. When VO 2 is in the insulated state, the absorber is in the closed state, Δf = 1.18 THz (absorption greater than 0.9); when VO 2 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.

Utilizing the phase transition principle of VO 2 , 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 VO 2 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 VO 2 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.

In this paper, ZnO@MoS 2 core-shell heterojunction arrays were successfully prepared by the two-step hydrothermal method, and the growth mechanism was systematically studied. We found that the growth process of molybdenum disulfide (MoS 2 ) was sensitively dependent on the reaction temperature and time. Through an X-ray diffractometry (XRD) component test, we determined that we prepared a 2H phase MoS 2 with a direct bandgap semiconductor of 1.2 eV. Then, the photoelectric properties of the samples were studied on the electrochemical workstation. The results show that the ZnO@MoS 2 heterojunction acts as a photoanode, and the photocurrent reaches 2.566 mA under the conditions of 1000 W/m 2 sunshine and 0.6 V bias. The i-t curve also illustrates the perfect cycle stability. Under the condition of illumination and external bias, the electrons flow to the conduction band of MoS 2 and flow out through the external electrode of MoS 2 . The holes migrate from the MoS 2 to the zinc oxide (ZnO) valence band. It is transferred to the external circuit through the glass with fluorine-doped tin oxide (FTO) together with the holes on the ZnO valence band. The ZnO@MoS 2 nanocomposite heterostructure provides a reference for the development of ultra-high-speed photoelectric switching devices, photodetector(PD) devices, and photoelectrocatalytic technologies., Competing Interests: The authors declare no conflicts of interest.