Search Results (611)

Broadband antireflective surface technology constitutes a crucial technique in optoelectronic devices, playing a key role in reducing optical losses. Ultrafast laser processing provides a flexible route for fabricating micro-nano structures on metallic surfaces because it enables efficient fabrication, high spatial resolution, and minimal chemical consumption. This study uses a variable-angle scanning strategy to texture the copper surface, produce a series of antireflection arrayed micro-nano structures, and study the spectral reflectance characteristics of the copper surface. The results exhibit that 90° orthogonal scanning favors the formation of an arrayed microcone structure, which shows lower reflectance than the non-orthogonal scanning strategies in the 200–1300 nm band, with a minimum reflectance of 0.94%. The 60° and 45° cross-scanning based on the non-orthogonal strategy favors the formation of microcavity structures, and shows low reflectance in the 1300–2500 nm band, with the maximum reflectance remaining below 5%. Laser-induced periodic surface structures (LIPSS) are observed on the structures fabricated by all strategies. This work demonstrates that the scanning angle itself can be used to switch the dominant surface morphology and thereby tailor the spectral antireflection response, and lies in establishing a clear processing–structure–spectral response relationship for copper surfaces, which provides a designable route for wavelength-selective optical absorption in photothermal conversion, infrared detection, and sensing applications. Full article

The development of reproducible and stable plasmon-free substrates for surface-enhanced Raman scattering (SERS) is critical for practical applications in analytical chemistry. Transition metal dichalcogenides (TMDCs) have emerged as promising candidates due to their unique electronic properties, yet their performance is often constrained by the chemical inertness of their pristine basal planes. This work presents a systematic comparison of crystalline flakes and nanoparticles of tungsten diselenide (WSe₂) and tungsten ditelluride (WTe₂), prepared via liquid-phase ultrasonic exfoliation and non-equilibrium femtosecond pulsed laser ablation in liquid (PLAL), respectively. The results demonstrate that nanoparticle-based substrates consistently outperform their flake-based counterparts, achieving enhancement factors in the range of ${10}^4$. The superior performance of the nanoparticles is hypothesized to originate from the synthesis-induced defects and high-curvature regions in the nanoparticles shell which facilitates efficient, defect-mediated charge transfer between the substrate and the analyte. At the same time, the inner polycrystalline volume conserves the important characteristics of the bulk counterparts like excitons in semiconducting WSe₂ and broadband absorption in semimetallic WTe₂, which unblocks the tunable photothermal colloidal response. The study establishes morphology engineering through non-equilibrium synthesis as a powerful and generalizable strategy for designing high-performance, dual-function colloidal platforms, offering a pathway toward robust and reproducible analytical systems. Full article

Monitoring dissolved carbon dioxide (CO₂) in aquatic and sediment systems is critical for understanding carbon cycling and climate feedback. This study develops and characterizes a compact, low-cost microbolometer-based attenuated total reflectance (ATR) mid-infrared sensor for direct dissolved CO₂ measurement in liquid and soil-water environments. The system integrates a ZnSe ATR crystal with custom suspended SiN membrane microbolometers and uses evanescent-wave absorption at 4.26 μm with a broadband LED source and computational spectral reconstruction, eliminating the need for an interferometer. Calibration shows excellent linearity (R² ≈ 0.99) over 50–1000 ppm CO₂, with a practical limit of detection (LOD) of ~26–35 ppm at 5–25 °C. UV-induced CO₂ generation from soil-water mixtures was investigated across UV wavelengths, revealing UV-C (254 nm) as optimal, producing net ΔCO₂ ≈ 339 ppm above ambient levels in 30 min. Environmental factors (temperature 5–35 °C, pH 5–11, pressure 1–1.5 ATM, dissolved organic carbon) were systematically evaluated, confirming robust sensor performance (accuracy >90%, correlation r > 0.98 with reference instrument). This sensor represents the first integration of MEMS microbolometer detectors with ATR evanescent-wave spectroscopy for liquid-phase dissolved CO₂, enabling real-time monitoring and rapid sediment organic carbon assessment in a field-deployable platform. Full article

A graphene-based tunable broad-band terahertz (THz) metamaterial absorber is presented, exhibiting strong and stable absorption across a wide frequency range. The device employs an ultra-thin three-layer structure consisting of a metallic reflector, a dielectric spacer, and a patterned graphene metasurface with an asymmetric geometry. Through optimized structural parameters, the absorber achieves broad-band absorption exceeding 90% between 2.45 THz and 6.11 THz with a bandwidth of 3.66 THz, featuring three distinct resonant frequencies at 2.764 THz, 3.534 THz, and 5.41 THz, corresponding to peak absorption efficiencies of 97.26%, 96.96%, and 99.90%, respectively. Impedance matching and electric field analyses confirm that the enhanced absorption arises from the strong coupling of electric and magnetic resonances within the multilayer structure. Moreover, the absorber exhibits polarization-insensitive behavior under varying polarization angles and maintains high absorption stability for both TE and TM modes up to an incident angle of 60°, as verified by simulation results, and allows dynamic tunability through Fermi-level modulation. These characteristics highlight the absorber’s potential for advanced THz imaging, sensing, and stealth applications. Full article

This study proposes an effective method for realizing broadband-infrared (IR)-equivalent absorption using a metasurface constructed by shaping a metal–insulator–metal structure leading to a semi-opened nanocavity. The metasurface architecture is formed according to an optimized structural configuration and mature micro–nano-fabrication flow. Both the surface travelling and localized resonant wavefield accumulation excited by incident lightwaves in a broad wavelength range of 1–14 μm can be efficiently manipulated based on a dipole molecule antenna responding mechanism. An electromagnetic wavefield shielding effect within the semi-opened nanocavity and the standing-wave formation around the metasurface near-field based on an arrayed titanium–dielectric–titanium structure are examined in detail. The measured IR spectral absorption characteristics reveal that the metasurfaces based on an arrayed top titanium cap with the featured dimensions of 2.0 μm and 2.4 μm can be used to achieve an average equivalent IR absorptivity higher than 80% and 82%, respectively, across a broad wavelength range of 1.29–14 μm, which covers the traditional short-, medium- and long-wave IR bands. Full article

Two-dimensional MoTe₂ is applicable for near-infrared photodetection; however, low absorption in the visible range limits its performance. One way to overcome these limitations is by hybridizing with light-absorbing nanomaterials. In this study, we simulate a CdSe/ZnS quantum dot (QD)-sensitized MoTe₂ photodetector at the coupled electromagnetic and device level. COMSOL Multiphysics demonstrates that the heterostructure of MoTe₂/CdSe/ZnS on a SiO₂/Si substrate exhibits a broadband-visible enhancement in absorption due to QD exciton absorption and Fabry–Perot interferences in the silicon dioxide layer. A staggered type-I band alignment of the CdSe/ZnS/MoTe₂ interface was confirmed by COMSOL analysis, which also permits interfacial charge separation. Simulations of QD integration by Silvaco technology computer-aided design reveal that QD integration increases photocurrent through photogating and carrier transfer. The optimized device has a responsivity and detectivity of 1.3 × 10⁻³, 2 × 10⁻³ A/W, 9.4 × 10⁸, and 1.34 × 10⁹ Jones, and an external quantum efficiency of 0.31% and 0.394% at 520 and 630 nm, respectively, which is significantly better than pristine MoTe₂ photodetectors. These results demonstrate the potential of CdSe/ZnS/MoTe₂ heterostructures for high-performance broadband photodetection and establish a framework for correlating multiscale simulations with material properties and device performance. Full article

Low-frequency broadband electromagnetic wave absorption is a critical challenge for radar stealth materials, as traditional absorbent-based coatings often suffer from poor low-frequency performance or severe high-frequency degradation when optimized for low frequencies. This study proposes a novel ultra-thin broadband low-frequency absorber fabricated by depositing a periodic resistive layer onto a conventional absorbent-based wave-absorbing layer, which forms a tailored low-frequency conductive metasurface structure. The integrated coating achieves an ultra-thin total thickness of merely 0.4 mm while exhibiting excellent broadband absorption performance across multiple radar bands: it delivers an average reflection loss of −0.6 dB in the L-band (1–2 GHz), −2 dB in the S-band (2–4 GHz), −3.6 dB in the C-band (4–8 GHz), and maintains a stable average reflection loss of −2.8 dB in the X to Ku bands. Compared with single-layer absorbing materials of the same thickness, this material exhibits significantly improved absorbing performance in the S-band and C-band, and achieves a breakthrough from zero to effective absorption in the L-band. Meanwhile, it can be integrated with structural design to reduce radar cross section (RCS), showing excellent engineering application value. The key mechanism underlying the performance enhancement lies in the periodic resistive layer, which optimizes the broadband impedance matching of the entire coating system, effectively elevates the surface current density, and augments resistive loss and eddy current loss within the structure. This design strategy enables an effectively boost in S-band wave-absorbing performance with minimal compromise to the high-frequency absorption characteristics, thus meeting the stringent requirements for broadband radar wave absorption in practical engineering applications. Full article

A bidirectional infrared absorber leveraging the Fabry–Perot resonance within a cascaded metal-dielectric nano-film structure is proposed. The absorber integrates a top Ag–VO₂–SiO₂ film stack, an intermediate thin Ag metal layer, and a bottom Al₂O₃–Ti–Al₂O₃ layer, enabling switchable narrowband and broadband absorption under forward and backward illumination, respectively. Under front illumination, the structure exhibits a high narrowband absorption peak of 98% at a wavelength of 1110 nm when VO₂ is in its metallic state. In contrast, when VO₂ transitions to its insulating state, the absorption peak shifts to 1165 nm. Additionally, under back illumination, ultra-broadband absorption is achieved, covering a wavelength range of 1000–2760 nm with an average absorption of 98%. The proposed absorber demonstrates excellent absorption performance with structural simplicity and low manufacturing cost, offering great potential for applications in solar photovoltaic devices, photodetectors, and related fields. Full article

Earth has long served as a primary construction material because of its easy availability and low environmental impact. However, reliability of this material depends on the stabilization to enhance its strength, durability, thermal and acoustic performance. This study investigates the structural and environmental suitability of stabilized Dhahran soil in sustainable consruction. The soil samples were collected from the Eastern Province of Saudi Arabia and stabilized using cement and lime at dosages of 2.5%, 5%, 7.5%, and 10%. Experimental evaluations included unconfined compressive strength (UCS), durability under wet–dry cycles, thermal conductivity, and sound absorption. Results revealed that 10% cement stabilization achieved a UCS of 6.1 MPa after 28 days, while lime-stabilized samples failed to meet the 2 MPa structural threshold. Durability tests showed that as little as 5% cement provided sufficient resistance, with minimal weight loss under repeated cycles. Cement-stabilized specimens exhibited higher sound absorption at low frequencies, whereas lime-based mixes offered more balanced broadband performance. Thermal conductivity (TC) increased moderately with higher cement content, ranging from 0.311 to 0.388 W/m·K, reflecting improved densification and heat transfer efficiency. Overall, the findings demonstrated that Dhahran soil, when cement-stabilized, becomes a durable, structurally viable, and environmentally suitable building material, supporting its potential as a sustainable construction solution in arid regions. Full article

A dual-band flexible wearable MIMO antenna with two operating modes, namely low-frequency narrowband and high-frequency broadband, is proposed and investigated in this paper. The antenna is based on a polyimide (PI) flexible printed circuit (FPC) substrate and has a compact size (90 mm × 40 mm × 0.1 mm), enabling easy integration into helmet-mounted devices. The antenna elements are fed by a coplanar waveguide (CPW) and integrated with a ground decoupling structure, achieving an isolation of at least 23.4 dB between the two ports across the entire operating frequency band. In addition, the impedance-matching characteristics of the antenna under bending conditions and the Specific Absorption Rate (SAR) of this MIMO antenna in a 1 g human-tissue model at 3.7 GHz and 4.6 GHz were evaluated. The results indicate that the antenna’s key electromagnetic performance remains relatively stable under bending conditions, and the SAR values comply with international limit requirements, verifying its feasibility for application in head-worn terminals. With an impedance bandwidth of −10 dB, this antenna achieves dual-band coverage at 3.42–3.84 GHz (relative bandwidth of 11.6%) and 4.37–7.80 GHz (relative bandwidth of 56.4%), effectively meeting the requirements of 5G/6G communication frequency bands. Full article

Digital transformation reshapes firms into more digital, data-driven, and customer-centric organizations. Because it often supports innovation, firms are widely expected to benefit from higher performance and productivity. However, it remains unclear whether higher national levels of digital integration translate into higher aggregate enterprise productivity. This study adopts a socio-technical and ecosystem perspective to examine the relationship between digital technology integration and enterprise labor productivity across the 27 EU member states, while also considering the role of key ecosystem enablers. A balanced country-year panel of data (N = 162) was constructed from Eurostat Structural Business Statistics on the apparent labor productivity of total enterprises, together with Digital Economy and Society Index (DESI) indicators on the integration of digital technology, human capital, connectivity, and Gross Domestic Product (GDP) per capita, covering the period from 2017 to 2022. To this end, fixed-effects regression models were estimated using robust standard errors clustered by country and combined with correlated random effects (CRE/Mundlak) decomposition. This methodological approach was adopted to distinguish short-run within-country dynamics from persistent between-country differences. The study contributes to ecosystem-level DESI research by using this distinction to assess how country-level digital integration is associated with enterprise productivity. The fixed-effects results provide no evidence that year-to-year changes in digital technology integration, on their own, are associated with higher enterprise productivity. Additionally, no statistically significant interaction effect was observed with either human capital or digital connectivity. By contrast, GDP per capita was found to be a robust positive predictor of enterprise productivity. The CRE/Mundlak results indicate that the majority of between-country productivity differences are attributable to differences in economic development. Furthermore, there is evidence of a positive association between the average level of digital technology integration and human capital. Taken together, these findings suggest that national digital technology integration reflects business environment conditions at the ecosystem level. While it may create opportunities for enterprise business model innovation, its productivity implications are more likely to emerge gradually through stronger absorptive capacity and complementary capabilities. Consequently, the study suggests that enterprise digital transformation policies should be aligned with investments in digital skills and broadband infrastructure. These policies should also support process redesign, greater interoperability, and the implementation of AI-enabled technologies. Full article

Non-invasive assessment of tissue water content is clinically relevant for edema detection, fluid management, and monitoring of local inflammation. In the short-wave infrared (SWIR), water exhibits strong absorption near 1450 nm with a secondary band near 1650 nm, enabling hydration-sensitive reflectance measurements. However, many SWIR systems rely on spectrometers or high-power broadband sources, limiting translation to compact or wearable platforms. We present a compact SWIR diffuse-reflectance probe built from small-form-factor components using four discrete LEDs (1450 nm and 1650 nm) and a single photodetector to acquire spatially resolved measurements at two source–detector separations (4.5 mm and 7 mm). Probe-geometry-matched Monte Carlo simulations were used to generate lookup tables relating reduced scattering to same-wavelength spatial ratios. A diffusion-based forward model was then used to perform a calibration-anchored water-fraction consistency analysis. Eight gelatin–Intralipid phantoms spanning two scattering conditions and formulation-defined water fractions were evaluated. Spatial-ratio signatures were repeatable and monotonic with nominal water fraction, yielding a mean absolute percent error of 1.55% and a maximum absolute percent error of 3.33% under absorption-consistent conditions. These results demonstrate the feasibility of compact SWIR ratio sensing for controlled hydration changes in tissue-mimicking phantoms and provide a modeling framework for future extension to unknown or in vivo samples. Full article

Self-powered photodetectors are highly demanded in applications but often suffer from limited spectral absorption, slow response speed, and high dark currents. Two-dimensional van der Waals heterostructures have emerged as promising candidates owing to their designable structures and excellent performance. Herein, we construct a MoTe₂/Bi₂Te₃ heterostructure and investigate its photoelectric properties. At zero bias, it exhibits a broad photovoltaic response ranging from 405 to 1550 nm. Benefiting from the interfacial built-in electric field, it achieves a responsivity of 1.38 A/W and a detectivity of 1.90 × 10¹² Jones at 532 nm and retains 174.56 mA/W and 2.4 × 10¹¹ Jones at 1060 nm, together with a low dark current of 1.6 × 10⁻¹² A. Upon a reverse bias of −1 V and 532 nm laser illumination at an intensity of 19.0 W/m², the responsivity is further boosted to 36.22 A/W, accompanied by rise and decay times of 32 ms and 33 ms, respectively. Taking advantage of the distinct optical switching ratios at zero/non-zero biases, application in optical imaging and bias-controlled signal modulation is realized, highlighting the heterojunction’s potential as a broadband self-powered photodetector. Full article

In the current paper, the nonlinear absorption characteristics and laser modulation performance of the ternary anisotropic semiconductor material ZrGeTe₄ were successfully explored. The recovery time of the ZrGeTe₄-PVA thin film was measured to be 5.74 ps by the pump–probe technology. By employing ZrGeTe₄ as a saturable absorber, a passive mode-locked Yb-doped fiber laser was demonstrated for the first time. In the 1 µm mode-locked operation, the central wavelength was 1031.29 nm, the pulse repetition rate was 24.85 MHz, and the pulse width was 786.3 ps. In an Er-doped fiber laser operating at a wavelength of 1561.10 nm, the pulse width was as short as 1.26 ps with a repetition rate of 4.38 MHz. The results show that ZrGeTe₄ has excellent broadband nonlinear optical characteristics. Full article

This study proposes a novel coplanar spiral-varying-channel space-coiled acoustic metamaterial (CSV-SCAM) for efficient low-frequency noise control in the range of approximately 200–400 Hz. By integrating continuously graded spiral channels with secondary spiral branches, the proposed structure enables multi-stage acoustic impedance matching and enhanced thermo-viscous dissipation, effectively overcoming the bulkiness and limited low-frequency efficiency of conventional porous absorbers. Finite element simulations and impedance tube experiments demonstrate that the CSV-SCAM achieves near-unity deep-subwavelength sound absorption, with a peak sound absorption coefficient exceeding 0.99 around 750–850 Hz using a thickness of only 10 mm. Furthermore, hybrid configurations composed of units with different branch numbers significantly broaden the effective absorption bandwidth by more than 20% while maintaining high absorption levels. Compared with traditional Helmholtz resonators, the proposed metamaterial exhibits superior compactness, structural robustness, and design flexibility, providing a promising solution for practical low-frequency noise mitigation in space-constrained engineering applications. Full article