This paper presents the design, fabrication, and characterization of a broadband metamaterial absorber (MMA) capable of optical switching between high- and low-absorbing states. The proposed metasurface exhibits a wide absorption bandwidth ranging from 13 to 17.3 GHz, maintaining a high absorption for wide incidence angles and for both transverse electric and transverse magnetic polarizations, demonstrating the polarization-insensitive performance. The metasurface is composed of periodically arranged unit cells integrated with photoresistors that enable tunable electrical resistance under optical illumination. When exposed to light, the photoresistors reduce their resistance, allowing the structure to achieve a high absorption. In the absence of illumination, the increased resistance suppresses the absorption response, effectively switching the metasurface to be a reflective state. This optically controllable behavior provides a simple and efficient approach for realizing dynamically reconfigurable MMAs, offering potential applications in adaptive stealth technology, electromagnetic shielding, and tunable sensing systems.

This paper introduces a vanadium dioxide-integrated broadband metamaterial absorber designed for the terahertz frequency range. The simulation results for the proposed structure demonstrate a wide 90% absorption bandwidth of 8.23 THz, corresponding to a fractional bandwidth of 89.5%. By leveraging the phase-transition properties of VO2, the absorber demonstrated dynamic adjustability by modulating the absorption from 3% to 98.74%. The absorption mechanism was analyzed through the impedance matching theory and electromagnetic field distributions, confirming the role of magnetic resonance and interference. Furthermore, machine learning algorithms, specifically Linear Regression, Support Vector Regression, and Random Forest (RF), were applied to accelerate the design process and optimize the structural parameters. Among these, the RF model demonstrated superior prediction accuracy. The machine learning-assisted optimization successfully extended the effective absorption bandwidth to 9 THz, representing an improvement by 9.4% compared to the traditional optimization methods. These results validate the efficacy of combining electromagnetic simulation with data-driven techniques for advanced metamaterial design.

Abstract The function of a new grating spectrometer with high spectral resolution was verified on the example of arsenic (As) lines. A continuous-wave direct-current arsenic hollow cathode lamp was employed as the light source. Real-time measurements were captured via integrated gratings and a two-dimensional backside-illuminated detector. Spectral lines from both neutral arsenic (As I) and singly ionized arsenic (As II) were successfully recorded across the ultraviolet and visible wavelength ranges with effective suppression of coma aberration. Wavelength calibration was performed with standard spectral lines from Hg and Mn atoms. Over 4000 spectral lines were detected in the wavelength range of 170–600 nm, of which 1129 lines were identified, including 59 spectral lines belongs to As I and As II. The uncertainty between the observed and calculated wavelengths across the entire spectral range was 0.015 nm. These identified lines correspond to electronic transitions between odd-parity levels 4 s 2 4 p 3 , 4 s 2 4 p 2 np and even-parity levels 4 s 4 p 4 , 4 s 2 4 p 2 ns .

Photocurrent scanning imaging (mapping) technology is a key technique in the research of solar cells and photodetectors. However, traditional galvanometer-driven beam scanning methods are limited by a restricted scanning range and image distortion. To address these shortcomings and meet the need for testing the photocurrent uniformity of large-area optoelectronic devices, an automated photocurrent mapping testing system has been developed based on opti- cal component scanning. This system offers a large imaging range, high spatial resolution, high stability, and low cost. With its high-precision mode, it can achieve sub-micron geometric positioning (subdivision number 6400, scanning step size 0. 625 mu m), fulfilling both large-area scanning requirements and providing high-resolution testing. Moreover, its simple structure greatly reduces the overall cost of the mapping system. Using a silicon solar cell sample with a white paper surface covered by the character "(sic)" (south) or an encoder strip mask, it was demonstrated that the scanning range exceeded 10 & times;10 mm(2), with a spatial resolution of 0.6 mu m. The system was also used to characterize the surface photocurrent images of Cu2ZnSnS4 and Cu2ZnSn(S,Se)(4) solar cells. The results show that the Cu2ZnSnS4 cell contains more defects, while the Cu-2 ZnSn(S,Se)(4) cell exhibits a more uniform surface photocurrent response with fewer defects. These findings contribute to the optimization of solar cell fabrication processes.

Reconfigurable photonic metasurfaces enable tunable thermal-emission engineering in the long-wave infrared (LWIR), particularly within the 8–13 μm atmospheric window. This work includes the investigation on a concentric-ring VO2/SiO2/Au metasurface for LWIR spectral-emissivity modulation. Full-wave simulations showed that, in the metallic phase (σ = 2 × 105 S/m where σ is conductivity), the structure exhibited an absorption over 90% across the 9.3–15 μm sub-band, with two near-unity resonances near 10.2 and 13.3 μm. Control structures, gap-dependent spectra, E-field maps, and current-density Cartesian multipole decomposition supported a hybridized-ring mechanism in which both dominant resonances were predominantly electric-dipole-like ring branches whose spectral positions and field localizations were modified by inter-ring coupling. Across the conductivity sweep, the normal-incidence band-averaged 8–13 μm emissivity changed from 0.0184 to 0.8844, corresponding to a switching ratio of 48.06. The four-fold symmetry of unit cell also yielded polarization-insensitive and angularly robust LWIR absorption, while the simplified endpoint thermal-balance estimate indicated a metallic-state net cooling power of 49.3 W m−2 at T = Tamb = 300 K, where Tamb was the ambient temperature, and an estimated equilibrium temperature drop of 4.4 K below the ambient for the metallic-state endpoint, whereas the insulating-state one suppressed this response. These results identify concentric VO2 ring metasurfaces as promising candidates for switchable LWIR thermal-emission control.

The spectra of neutral arsenic (As I) and singly ionized arsenic (As II) covering the ultraviolet and visible wavelength range were measured with a coma-free grating spectrometer. Real-time measurements were captured via integrated gratings and a two-dimensional backside-illuminated detector. Wavelength calibration was performed with standard spectral lines from Hg and Mn atoms. The light source for observing the arsenic spectra was a continuous direct-current arsenic hollow cathode lamp. Over 4000 spectral lines were detected in the wavelength range of 170–600 nm, of which 1138 lines were identified, including 59 spectral lines belongs to As I and As II. The uncertainty between the observed and calculated wavelengths across the entire spectral range was 0.015 nm. These identified lines correspond to electronic transitions between odd levels 4s2 4p3, 4s2 4p2ns and even levels 4s 4p4, 4s2 4p2ns, and 4s2 4p2np.

Radiative cooling is a passive cooling strategy that dissipates heat externally through the atmospheric window (8–13 μm). This study presents a radiative cooling film with a simple and cost-effective fabrication process. The film was fabricated by mixing SiO₂ hollow microspheres with a UV-curable resin, employing a photopolymerization-induced phase separation method. The resulting gradient refractive index structure enhanced thermal radiation emissivity. At an optimal silica-to-resin mass ratio of 1:1.5 and a film thickness of 1.1 mm, the film achieved a solar reflectivity of 85% and an emissivity of 91% within the atmospheric window. Outdoor experiments conducted in both summer and winter demonstrated stable cooling performance. Under a solar irradiance of 796.9 W/m2 (summer), the film reduced surface temperature by 10 °C compared to ambient air and 20 °C compared to an uncoated glass substrate, achieving a radiative cooling power of 76.7 W/m2. In winter (solar irradiance of 588.8 W/m2), the film maintained a significant cooling effect, though with reduced efficiency due to lower solar exposure. Furthermore, long-term stability tests over six months showed that the film retained high solar reflectivity and infrared emissivity, indicating good durability. Overall, the developed radiative cooling films demonstrate excellent optical properties, structural stability, and cooling efficiency, making it a promising candidate for real-world radiative cooling applications. Further studies on environmental resilience and optimization under diverse climatic conditions are necessary for broader deployment.

Vanadium and oxygen form a complex system of vanadium oxides with multiple phases and mixed valency, increasing the difficulty of characterization. In this work, amorphous vanadium oxide thin films with mixed valence states were fabricated by atomic layer deposition, and then post-annealing was conducted for crystalline films. For the surface analysis of this mixed-valence system, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were employed. However, XPS is only able to quasi-quantitatively determine the surface-proximity oxidation states. To account for the inadequacy of surface-sensitive XPS and AES techniques, a surface oxidation model (SOM) was proposed for the ellipsometric modeling of the mixed-valence system. Furthermore, by conducting air thermal oxidation (ATO) experiments, the four sets of fitting parameters of SOM were decreased to three, lowering the system complexity. This study is expected to help with the analysis of vanadium oxide mixed-valence systems and other multivalent metal oxide systems.

As a passive cooling method, radiative cooling is intrinsically energy-efficient and environmentally friendly because it consumes no electric energy and releases no carbon emissions. Smart radiative cooling introduces a new dimension to the current research playground, especially with the use of vanadium dioxide (VO2) to enable passively adaptive temperature-varying response. Here, we propose a temperature-adaptive radiative cooling metasurface based on a two-size VO2 microstructure for broadband absorption in the 8 to 13 mu m atmospheric window, showing a cooling power contrast of similar to 100 W/m(2) around the phase transition temperature. We show the dynamic capability of the next-generation multifunctional and intelligent designs and devices. (c) 2025 Society of Photo-Optical Instrumentation Engineers (SPIE)

This study was conducted to investigate the effect of hydrogenation on the Poisson’s ratio of biphenylene. By combining large-scale molecular dynamics simulations with a stochastic structure generation method, this study revealed that the Poisson’s ratio of biphenylene can shift from positive to negative as the degree of hydrogenation is adjusted. Specifically, at lower hydrogenation levels, the Poisson’s ratio decreases with increasing hydrogenation, eventually exhibiting a negative Poisson’s ratio at 40% to 50% hydrogenation. However, as hydrogenation progresses further, the negative Poisson’s ratio effect diminishes. The occurrence of negative Poisson’s ratio in hydrogenated biphenylene is attributed to a pronounced ripple effect induced by hydrogenation. Under tensile strain, the suppression of ripples reduces contraction in the direction perpendicular to the applied stretch. Moreover, the findings highlight a strong correlation between the ripple effects in the structure and the percentage of hydrogenation. These results demonstrate that hydrogenation serves as an effective approach to modulate the Poisson’s ratio of biphenylene, enabling its transition from positive to negative.

This study addresses the challenges of high-power consumption and complexity in conventional infrared (IR) gas sensors by integrating metamaterials and gold coatings into IR radiation sources to reduce radiation loss. In addition, emitter design optimization and material selection were employed to minimize conduction loss. Our metasurface exhibited superior performance, achieving a narrower full width at half maximum at 4197 and 3950 nm, resulting in more confined emission spectral ranges. This focused emission reduced energy waste at unnecessary wavelengths, improving efficiency compared to traditional blackbody emitters. At 300 °C, the device consumed only 6.8 mW, while maintaining temperature uniformity and a fast response time. This enhancement is promising for the operation of such sensors in IoT networks with ultra-low power consumption and at suitably low costs for widespread demands in high-technology farming.

Absorption of electromagnetic waves in a broadband frequency range with polarization insensitivity and wide incidence angles is greatly needed in modern technological applications. Many methods using metamaterials have been suggested to address this requirement; they can be complex multilayer structures or use external electronic components. In this paper, we present a plasmonic metasurface structure that was simply fabricated using the standard printed circuit board technique but provided a high absorption above 90%, also covering a broadband frequency range from 12.30 to 14.80 GHz. This plasmonic metasurface consisted of structural unit cells composed of multiple split rings connected by a copper bar. Analysis, simulation, and measurement results showed that the metasurface also showed polarization-insensitive properties and maintained an absorption above 90% at incident angles up to 45 degrees. The suggested plasmonic metasurface is a fundamental design that can also be used to design the absorber in different frequency ranges and is able to adapt well to being fabricated at various scales.

Photothermal conversion is a pivotal energy transformation mechanism in solar energy systems. Achieving high-efficiency and broadband photothermal conversion within the solar radiation spectrum holds strategic significance in driving the innovative development of renewable energy technologies. In this study, a transmission matrix method was employed to design an interference-type solar selective absorber based on multilayer Cr-SiO2 planar films, successfully achieving an average absorption of 94% throughout the entire solar spectral range. Further analysis indicates that this newly designed absorber shows excellent absorption performance even at a relatively large incident angle (up to 60°). Additionally, the newly designed absorber demonstrates lower polarization sensitivity, enabling efficient operation under complicated incident conditions. With its simple fabrication process and ease of preparation, the proposed absorber holds substantial potential for applications in photothermal conversion fields such as solar thermal collectors.

The metal–insulator transition of vanadium dioxide (VO2), a phase change material, has been utilized for various applications. The characterization of the VO2 thin film structure, in both its optical properties and thickness, remains a critical problem. In this paper, VO2 thin films were fabricated on silicon substrates by magnetron sputtering. By using temperature-varying spectroscopic ellipsometry, VO2 thin films of different thicknesses were characterized in an energy range of 0.5–3.0 eV, and the phase change temperature was determined using ellipsometry data. The optical properties of these samples were determined from temperature-dependent ellipsometry measurements by using the Drude and multiple Tauc–Lorentz model. Broadband temperature-dependent reflectivity spectra were obtained. An analysis of the samples revealed that their bandgaps, plasma frequencies, and other modeling parameters demonstrated a pattern of change with increasing temperature, which could be explained by the underlying physics. This study will help with the design of VO2-based structures for a broad range of applications.

2D materials and heterojunctions have extraordinary potential in the field of next-generation integrated photodetectors. Recently, inserting graphene (Gra) into van der Waals heterojunctions as transport layers has been proven to be an effective method for improving the responsivity and response speed of photodetectors. However, how did the physical mechanisms caused by the insertion (interlayer coupling and electron transfer) regulate its optical properties are unclear. Meanwhile, whether the insertion will modulate the broadband optical properties of the heterojunction should also be carefully verified. In this work, the broadband (1.25-6.50 eV) electronic band structures and exciton properties of MoS2/WSe2 and MoS2/Gra/WSe2 were studied using spectroscopic ellipsometry, meanwhile Raman and PL spectroscopy were used to assist in analysis. We found that graphene insertion not only promote the spontaneous charge transfer from WSe2 to MoS2, but also effectively inject electrons into the MoS2 layer, which benefits the interlayer charge separation and net charge accumulation in MoS2. Moreover, the almost stable CP energies near the band edge represent that graphene insertion does not change the electronic band structures of MoS2/WSe2. Furthermore, due to the increasing effective dielectric screening induced by graphene insertion, the exciton binding energies redshift and the exciton transition energy blueshift consequently.

The absorption of electromagnetic waves in a broadband frequency range with polarization insensitivity and incidence-angle independence is greatly needed in modern technology applications. Many structures based on metamaterials have been suggested for addressing these requirements; these structures were complex multilayer structures or used special materials or external electric components, such as resistive ones. In this paper, we present a metasurface structure that was fabricated simply by employing the standard printed-circuit-board technique but provides a high absorption above 90% in a broadband frequency range from 12.35 to 14.65 GHz. The metasurface consisted of structural unit cells of 4 symmetric substructures assembled with a metallic bar pattern, which induced broadband absorption by using a planar resistive interaction in the pattern without a real resistive component. The analysis, simulation, and measurement results showed that the metasurface was also polarization insensitive and still maintained an absorption above 90% at incident angles up to 45°. The suggested metasurface plays a role in the fundamental design and can also be used to design absorbers at different frequency ranges. Furthermore, further enhancement of the absorption performance is achieved by improved design and fabrication.

A two-dimensional guided mode resonance structure supports a transverse magnetic (TM) resonant mode in the direction of incident polarization and a transverse electric (TE) resonant mode in the direction perpendicular to the polarization. In this work, the coupling between the transverse magnetic and the transverse electric resonant modes in an asymmetric two-dimensional dielectric metasurface structure is investigated. The asymmetric structure consists of a two-dimensional square nanohole array etched in a titanium dioxide thin film on a transparent silica substrate. With finite difference time domain simulations, anti-crossing of the resonant spectra of the TM and TE modes is observed by adjusting the asymmetry of the structure. The anti-crossing indicates that the interaction between TM and TE resonant modes results in a strong coupling state. A coupled harmonic oscillator model is used to explain the strong coupling effect. The results of the coupled harmonic oscillator modeling agree well with the results of numerical simulations. Furthermore, it is shown that the strong coupling can significantly enhance the third harmonic generation intensity compared with the uncoupled TM and TE resonant modes.

Our study introduces a metamaterial with a straightforward disk-like configuration that exhibits two prominent absorption peaks at wavelengths of 3960 and 4197 nm, with absorption of 96.3% and 94.1%, respectively. The design not only proved to be convenient for the practical fabrication, but also revealed a resilience to the changes in structural parameters. Moreover, this offers versatility across a wide range of applications, due to the polarization-independent behavior. Additionally, the investigation on thermal emission by integrating the metasurface on a spiral structured heat source has yielded a promising result. The metasurface emitter reduced the energy consumption by 35%, compared with the blackbody emitter. The emission intensity at the aforementioned wavelength is 1.75 x 109 and 1.8 x 109 W center dot sr-1 center dot m-3, respectively, indicating that the high potential of structure for the practical deployment in next-generation microheater of CO2 sensors.