Search Results (468)

In this work, a high-performance mid-wave infrared (MWIR) photodetector (PD) utilizing an InAs/GaSb Type-II superlattice absorber and a quaternary AlGaAsSb barrier is designed and analyzed based on numerical simulations aimed at determining an optimized detector structure. Through these simulations, the composition of the AlGaAsSb barrier is carefully designed to achieve lattice matching, high conduction band offset and zero valence band offset. By optimizing the barrier thickness and doping concentration, the depletion region is effectively shifted from the narrow-bandgap absorber to the wide-bandgap barrier; additionally, at 150 K and a reversed bias of 0.05 V, the dark current density in the PD with the barrier (pBn) is reduced to 1.83 × 10⁻⁵ A/cm², about two orders of magnitude lower than that of the PD without the barrier. Furthermore, the effect of the barrier on the generation–recombination (G-R) and the trap-assisted tunneling (TAT) currents are analyzed and compared in detail, and it is found that the barrier structure is much more effective in suppressing the TAT current at low reversed bias when the electric field is low in the absorber layer. These results demonstrate the efficacy of the proposed AlGaAsSb barrier design for realizing high-operating-temperature MWIR PDs. It also provides an insight into the physical mechanism that leads to the performance enhancement of InAs/GaSb PDs. Full article

Additive manufacturing enables the fabrication of personalized protective equipment with locally tailored mechanical properties. In this work, a low-cost scan-to-print workflow is proposed for the fused filament fabrication (FFF) of personalized dual-zone shin guards combining a stiff outer load-distribution layer with a compliant inner energy-absorbing layer. Subject-specific leg geometry was acquired via structured-light 3D scanning and used to design a shin guard with two 3.5 mm thick zones (total thickness 7 mm). Foamable filaments of PLA, ASA, and TPU were employed to manufacture unfoamed and foamed regions by controlling extrusion temperature. Mechanical performance was assessed through three-point bending tests and dynamic finite element impact simulations. Unfoamed PLA and ASA exhibited flexural strengths of approximately 88 MPa and 72 MPa, respectively, while foaming reduced these values by about 74%. Dual-zone configurations partially restored stiffness, reaching 41 MPa for PLA and 29 MPa for ASA. TPU showed lower flexural stresses with a smaller reduction of 23% upon foaming. Impact simulations revealed maximum deformations of 1.97 mm and 2.02 mm for PLA and ASA outer zones, respectively, while TPU exhibited large deformations leading to penetration of the 3.5 mm thick inner layer. The results demonstrate that dual-zone designs manufactured via foaming-enabled FFF can effectively balance stiffness, weight, and impact response for personalized shin guard applications. Full article

This work investigates the reciprocal adhesion of Polybenzoxazole (PBO) and silicon nitride (SiN) with a focus on the combined effects of surface chemistry and environmental conditions, i.e., temperature (T) and relative humidity (RH). A set of six samples, including standard and silicon-rich SiN substrates treated with oxygen (O₂) or carbon tetrafluoride (CF₄) plasma, was fabricated and characterized by AFM, XPS, and TEM/EDX to quantify surface roughness and interfacial chemical modifications. Adhesion with PBO was then assessed through nanoindentation both in situ, during ambient control, and ex situ, after aging in a climatic chamber. Compared to PBO adhesion with as-deposited standard and silicon-rich SiN, O₂ plasma treatment was shown to improve adhesion by 13% and 24%, respectively, whereas CF₄ plasma treatment was still beneficial but more limited, improving adhesion by 8% for both substrates. The different effects were ascribed to the formation of a surface oxide layer after O₂ plasma, enhancing chemical affinity and substantially equalizing the adhesion on the two SiN substrates, while CF₄ plasma was impacting adhesion by reducing the substrates’ activity and, thus, increasing the efficiency of the PBO curing procedure. Notably, the adhesion loss with increasing dew point of the ambient (dependent on temperature and relative humidity) was observed across all samples regardless of surface treatment, reinforcing the critical role of absorbed moisture on polymeric film adhesion. However, this trend was observed for all samples only for in situ testing, with a loss of 25% in the critical load of delamination for the most critical environment, while ex situ tests showed a marked recovery of adhesion properties, leading to measurements no longer reflecting the actual state of the samples inside the altered environment. The results presented in this paper highlight the effect of substrate preparation on the adhesion of an organic compound and a substantial difference in environmental control methods for adhesion testing, providing an alternative approach to classical aging treatments and subsequent characterization for qualifying polymer/inorganic interfaces exposed to stressful operational conditions. Full article

Two-dimensional (2D) Ruddlesden–Popper (RP) tin halide perovskites have attracted considerable attention as lead-free photovoltaic absorbers; however, the impact of organic A-site cations on their structure and pressure-dependent optoelectronic behavior remains underexplored. In this study, density functional theory (DFT) is used to investigate the structural, electronic, and optical properties of A₂SnI₄ (A = GUA⁺, DMA⁺, MA⁺) under ambient conditions and under hydrostatic pressure. All three compounds adopt layered frameworks in which the organic cations occupy the interlayer region, while SnI₆ octahedra form the inorganic slabs. Band-gap calculations are performed using HSE06 for ambient pressure, known for its accuracy in electronic structure predictions, and PBE for pressure simulations, due to its computational efficiency in large-scale systems. At ambient pressure, Hybrid-functional (HSE06) calculations indicate that all three materials are direct-gap semiconductors, with band gaps of 2.25 eV for MA2SnI₄, 2.98 eV for DMA2SnI4, and 2.85 eV for GUA2SnI4. Under hydrostatic compression, DMA₂SnI₄ shows comparatively modest band-gap variation and saturates near 1.7 eV. In contrast, GUA₂SnI₄ and MA₂SnI₄ exhibit pronounced band-gap narrowing, including a pressure-induced direct-to-indirect transition near 2 GPa, with band gaps decreasing to 0.59 eV (GUA₂SnI₄) and 0.34 eV (MA₂SnI₄) at elevated pressures. Overall, these findings highlight that A-site chemistry, combined with hydrostatic pressure, enables tuning the electronic and optical responses in tin-based 2D RP perovskites, demonstrating their promise as tunable, lead-free photovoltaic absorbers. Full article

This study assessed natural radioactivity values and corresponding radiological hazards in gypsum samples collected from the investigated area. The geologic context mainly includes tertiary and quaternary sedimentary formations with gypsum horizons of Early Messinian age, interbedded with layers of limestone and marl. A total of thirty-five gypsum samples were collected and analyzed for the ²³⁸U, ²³²Th, and ⁴⁰K activity concentration using High-Purity Germanium (HPGe) gamma-ray spectrometry. The mean activity concentrations for the gypsums are reported at 73 ± 87 Bq kg⁻¹, 14 ± 17 Bq kg⁻¹, and 35 ± 201 Bq kg⁻¹ for ²³⁸U, ²³²Th, and ⁴⁰K, respectively. Several related radiological hazard indices were estimated from the various activity concentrations, including radium equivalent activity (Ra_eq) and absorbed dose rate (D_air). All gypsum analyzed fell below international safety limits for radiological risk, as evidenced by the observed radium equivalent activity (Raeq), with a maximum value of 456 Bq kg⁻¹, and the total annual effective dose (AED) values from 0.09 to 1.26 mSv y⁻¹ remaining between these two values. The results indicate the levels of radioactive hazards of the gypsum samples were generally below global safety standards, but individual samples (i.e., S17, S20, S24, S26, S30, S35) exceeded one or more of the hazard indices. Statistical assessment of the samples, with respect to their radiological hazard and natural radioactivity, was also undertaken as a way of seeking further insights into their relationships, productivity, and characteristics. This included Pearson correlation, hierarchical cluster analysis (HCA) and principal component analysis (PCA). The evidence suggests that for the gypsums, ²³⁸U was the greatest contributor to radiological hazards, influencing all hazard indices. Full article

In this work, we report a protective encapsulation intended as the final coating layer on solar cells. The formulation consists of polylactic (PLA)-based resin, modified with hexadecyltrimethoxysilane (HDTMS), epoxidized polybutadiene (EPB), and benzotriazole as a UV absorber with approximate weight fractions ranging from 20 to 60 wt% for PLA, 30–80 wt% for solvents (toluene and chloroform), and 0–5 wt% for HDTM, EPB, and benzotriazole with percentages 54.2%, 29.2%, and 16.7%, respectively. The encapsulating material, due to its insulating nature and high optical transparency, surpasses that of ethylene–vinyl acetate (EVA), as demonstrated in this study. To assess the protective effect of the developed formulation, the study focused on applying the modified PLA resin onto isolated methylammonium lead iodide (MAPI) perovskite films on glass substrates. The samples were prepared as isolated MAPI absorbers to specifically assess the intrinsic contribution of the dual encapsulation configuration at its real position in a complete solar cell stack, demonstrating that even this unoptimized perovskite film exhibits remarkable stability and excellent structural and optical retention over two months under the protective scheme (86% of its initial structural stability, as quantified from integrated XRD peak intensities, and 68% of its initial optical absorbance, determined from the integrated UV–Vis spectra), whereas the uncoated films showed significant degradation. Although MAPI was selected as a model system due to its well-known environmental instability, the proposed encapsulation material and methodology are not limited to this architecture and can, in principle, be applied to various photovoltaic technologies. These findings demonstrate the strong potential of the polylactic-based resin as an effective environmental barrier for solar cells and provide a solid foundation for future full-device integration studies. Full article

This study investigates the state of the art related to the computational methods for solar cells. Numerical modeling is a basic pillar that is used to ensure the robust design of any device. In this paper, the results of a detailed science mapping-based analysis on the publications that focus on the “numerical modelling of solar cells” are presented. The query was conducted on the Web of Science for 2014–2024, and a subsequent filtering was performed. The results of this analysis provided the answers to the five research questions posed. The paper has been divided into two parts. In the first part, the literature search began with a broad examination, and 3259 studies were included in the analysis. To present the results in a visual form, graphs created using VOS viewer software have been used to identify the pattern of co-authorship, the geographical distribution of the authors, and the keywords most frequently used. In the second part, the analysis focused on three main aspects: (i) the influence of absorber layer thickness on optical absorption and device efficiency, (ii) the role of different ETL/HTL materials in charge transport, and (iii) the effect of illumination conditions on carrier dynamics and photovoltaic performance. By integrating the results across these dimensions, the study provides a comprehensive understanding of how these parameters collectively determine the efficiency and reliability of perovskite solar cells. Full article

This work presents the first study addressing two-dimensional numerical simulations of acoustic wave scattering involving a simplified human body model placed inside an enclosed cabin. The simulations utilise the µ-diff backscattering algorithm in MATLAB, which is suitable for modeling frequency-domain interactions with multiple scatterers under penetrable boundary conditions. The body is represented as a cluster of penetrable, tangent circular cylinders with acoustic properties mimicking muscle, fat, bone, and clothing layers. Hidden PVC cylinders are embedded to simulate concealed objects. Several configurations were examined, varying the number of PVC inclusions (two to four), the frequency range, and the presence of an absorbing cabin wall. Sound pressure level (SPL) distributions around the body and at a 1 m distance were analysed. Polar plots reveal distinct differences between the baseline body model and those incorporating PVC inclusions. The most pronounced effects occur near 160 Hz, where an absorbing wall is present within the acoustic enclosure. The presence of an absorbing wall modifies wave behaviour, producing enhanced directional attenuation. The results demonstrate how object composition, spatial arrangement, and enclosure geometry influence acoustic backscattered fields. These findings highlight the potential of wave-based numerical modelling for detecting concealed items on the human body in confined acoustic environments, supporting the development of non-invasive security screening technologies. Full article

Poly(lactic acid) (PLA)-based nanocomposites containing a mixture of graphene nanoplatelets (GNP) and carbon nanotube (CNT) as hybrid fillers were prepared using a solution-assisted sonication process followed by melt processing. The effects of the filler dispersion on dielectric properties and microwave absorbing (MWA) performance were systematically investigated. Two ionic liquids (ILs), trihexyl-(tetra-decyl)phosphonium bis (trifluoromethanesulfonyl)imide (IL1) and 11-carboxyundecyl-triphenylphosphonium bromide (IL2), were employed as dispersing agents for the carbonaceous fillers. Incorporation of IL-treated fillers resulted in enhanced dielectric permittivity and improved MWA performance of the PLA composites. The MWA properties were evaluated in X- band and Ku-band. A minimum reflection loss (RL) of −34 dB and an effective absorption bandwidth (EAB) of 2.1 GHz were achieved for the composite containing GNP/CNT/IL2 (HB3) at a weight ratio of 2.5:0.5:0.5 wt% with one 3 mm thick layer. The superior performance of IL2 is attributed to π-π and π-cation interactions between its phenyl-containing cation and the carbonaceous fillers, as well as improved compatibility with the PLA matrix due to carboxyl groups. Additionally, three-layered composite structures, combining PLA/GNP as the outer layer with IL-assisted hybrid fillers in the core and PLA/CNT at the bottom layer, achieved an extended EAB of 4.5 GHz for GNP/HB2/CNT arrangement and 4.35 GHz for the GNP/HB3/CNT arrangement, driven by enhanced scattering and internal reflection of microwaves. These results demonstrate the potential of IL-assisted hybrid filler dispersion in PLA for developing biodegradable materials with multifunctional applications as charge storage capacitors and microwave absorbing materials for sustainable electronics. Full article

The compounds LiCo_1−xMn_xO₂ (x = 0.5, 0.7) were synthesized via the solid-state method and exhibited crystallization in the cubic spinel structure (space group Fd-3m). UV–Vis spectroscopy reveals strong visible-light absorption and a reduction in the indirect optical band gap from 1.85 eV (x = 0.5) to 1.60 eV (x = 0.7) with increasing Mn content, which is consistent with semiconducting behavior. This narrowing arises from Mn³⁺/Mn⁴⁺ mixed valence, which introduces mid-gap states and enhances Co/Mn 3d–O 2p orbital hybridization within the spinel framework. In contrast, the Urbach energy increases from 0.55 eV to 0.65 eV, indicating greater structural and energetic disorder in the Mn-rich composition which is attributed to the Jahn–Teller distortions and valence heterogeneity associated with Mn³⁺. Impedance and dielectric modulus analyses confirm two distinct non-Debye relaxation processes related to grains and grain boundaries. AC conductivity is governed by the Correlated Barrier Hopping (CBH) model, with bipolaron hopping identified as the dominant conduction mechanism. The x = 0.7 sample displays significantly enhanced conductivity due to increased Mn³⁺/Mn⁴⁺ mixed valence, lattice expansion, efficient 3D electronic connectivity of the spinel lattice, and reduced interfacial resistance. These findings highlight the potential of these two spinels compounds as narrow-gap semiconductors for optoelectronic applications including visible-light photodetectors, photocatalysts, and solar absorber layers extending their utility beyond conventional battery cathodes. Full article

We present a numerical implementation of the proposed Source–Detector Resonance (SDR) as a conceptual analog of a Double-Slit Interference Experiment with discrete particles. Two periodic streams of particles are emitted from two point sources at random integer multiples of a fundamental period P and corresponding frequency $\omega =2\pi /P$ and fly out towards a detection screen. The screen consists of a deep set of identical oscillators with eigenfrequency ${\omega }_0=2\pi /P_0$. In the SDR scenario, $\omega \approx {\omega }_0$. When the particles reach the screen, they implement a periodic forcing of its oscillators at the stream’s fundamental frequency ${\omega }_0$. As a result, an oscillating pattern develops along the screen. The amplitude of oscillation of each oscillator saturates at a value that is determined by the balance between the periodic particle forcing and the damping of each oscillator. This is clearly proportional to the number of particles that reach a certain oscillator per unit time times the fraction of particles that reach it at its resonant frequency. The latter fraction is equal to the ratio of the Power Spectral Density (PSD) of the time series of the particles that reach the oscillator at its resonance frequency PSD(${\omega }_0$) over the PSD at zero frequency PSD(0). If we further assume that each oscillator absorbs a particle and announces a detection with a probability that is proportional to the square of the ratio PSD(${\omega }_0$)/PSD(0); the pattern of particle detections that develops over a thick layer of oscillators is shown to be the same as that of a Double-Slit Interference Experiment. Our result shows that when macroscopic resonant detectors interact with and detect periodic streams of discrete particles, they may create the illusion of an interference measurement, as if each discrete particle manifests a phase of its own. Full article

Bio-oil’s high chlorine content severely hinders its application, because of its high corrosivity. Catalytic pyrolysis is an effective method for the dechlorination of bio-oil. Herein, the performances of the acidified-γ-Al₂O₃ modified with alkaline and alkaline earth metal compounds were investigated. It was found that NaOH was a better loading material than Ca(NO₃)₂ or Mg(NO₃)₂ in the support of acidified-γ-Al₂O₃. The optimal loading amount of NaOH was 5 wt% in the range of 1 wt%–15 wt%, and the better calcination temperature was 600 °C, compared with 800 °C. When catalyzed with Na/Al₂O₃ (5%, 600 °C), the organic chlorides content in bio-oil from the pyrolysis of corn straw at 500 °C was significantly reduced from 150 ppm to 29 ppm, while the inorganic chlorides content barely changed. NaAlO₂ was generated in Na/Al₂O₃ from the solid-phase reaction between NaOH and Al₂O₃ by calcination. When Na/Al₂O₃ (5%,600 °C) and Na₂CO₃ were both used in two layers in a fixed-bed reactor, the organic and inorganic chlorides in bio-oil simultaneously significantly decreased, respectively, to 57 ppm and 23 ppm. The decrease in chlorides benefits the deep dechlorination of bio-oil by absorption or catalytic hydrodechlorination in a post-treatment process, which reduces the consumption of absorbent or hydrogen. Full article

This paper presents a checkerboard-patterned terahertz (THz) metamaterial absorber engineered for wide-band, dual-band absorption. The absorber consists of a gold metal layer patterned on a polyimide substrate, forming a unit cell structure with dimensions of 85 µm × 85 µm. At the core of the design is a square metal patch of 67 µm × 67 µm, which is divided into a 5 × 5 grid of 25 smaller cells. An integer-coded Particle Swarm Optimization (PSO) algorithm is employed to generate the pattern, where an input value of ‘1’ retains the metal in a cell, and a ‘0’ results in the removal of metal from that cell, resulting in a digitally optimized checkerboard pattern. The substrate height is also optimized and fixed at 7 µm to enhance resonance characteristics. The PSO algorithm is run for 50 iterations, with the fitness function defined as the number of frequency points at which the absorption exceeds 90%. The finalized design achieves two distinct absorption peaks with high efficiency: 99.53% at 3.434 THz, with a 90% absorption bandwidth of 212 GHz; and 99.35% at 3.823 THz, with a bandwidth of 177 GHz. While the absorption performance is already significant, it can be further improved by increasing the number of PSO iterations, albeit at the cost of higher computational complexity. The proposed absorber demonstrates strong potential for biomedical sensing, as validated through its ability to differentiate between cancerous and non-cancerous breast and blood cells. This work paves the way for fully automated, algorithm-driven metamaterial design strategies in the THz regime, particularly for applications in non-invasive biomedical diagnostics. Full article

Gradient stiffness structures are increasingly recognized for their excellent energy absorption capabilities, particularly under challenging loading conditions. Most studies focus on varying the thickness of the structure in order to produce gradient stiffness. This work introduces an innovative approach to design honeycomb architectures with controlled gradient stiffness along the out-of-plane direction achieved by materials’ microstructure variations. The gradient is achieved by combining three types of thermoplastic polyurethane (TPU) materials: porous TPU, plain TPU, and carbon fiber (CF)-reinforced TPU. By varying the material distribution across the honeycomb layers, a smooth transition in stiffness is formed, improving both mechanical resilience and energy dissipation. To fabricate these structures, a dual-head 3D printer was employed with one head printed processed TPU with a chemical blowing agent to produce porous and plain sections, while the other printed a CF-reinforced TPU. By alternating between the two print heads and modifying the processing temperatures, honeycombs with up to three distinct stiffness zones were produced. Compression testing under out-of-plane loading revealed clear plateau and densification regions in the stress–strain curves. Pure CF-reinforced honeycombs absorbed the most energy at stress levels above ~4.5 MPa, while porous TPU honeycombs were more effective under stress levels below ~1 MPa. Importantly, the gradient stiffness honeycombs achieved a balanced energy absorption profile across a broader range of stress levels, offering enhanced performance and adaptability for applications like protective equipment, packaging, and automotive structures. Full article

Soil moisture (SM) is crucial for ecosystems and agriculture. Since the root systems of plants absorb water at different depths with different intensities, monitoring multi-layer SM can better respond to the water demand of plants and offer a crucial technical backing for drought monitoring and precision irrigation. Synthetic aperture radar (SAR) and multispectral (MS) have been widely used in SM estimation; however, their combined application for multi-layer SM profiling remains underexplored. Existing research based on these two data types has primarily focused on surface soil moisture (SSM), with limited investigation into estimating SM at deeper or varying depths. Therefore, the aims of this research are to integrate Sentinel-1 SAR and Sentinel-2 MS data and employ machine learning algorithms to estimate multi-layer SM in the Shandian River Basin. The results showed that (1) MS + SAR-based SM estimation significantly outperformed single-source data (MS or SAR alone). Specifically, MS data performed better in the root-zone estimation, while SAR data showed superior performance in SSM estimation. (2) The BKA-CNN estimation accuracy significantly outperformed RF and XGBoost. The results of its five-fold cross-validation are as follows: R² = 0.768 ± 0.011 at 3 cm, R² = 0.777 ± 0.013 at 5 cm, R² = 0.799 ± 0.011 at 10 cm, R² = 0.792 ± 0.01 at 20 cm, and R² = 0.782 ± 0.011 at 50 cm. (3) The BKA-CNN model performed better in grassland than in farmland. These findings indicate that the BKA-CNN model proposed in this study effectively improves the estimation precision of multi-layer SM by fusing SAR and MS data, demonstrating considerable generalization ability and robustness. It holds potential application value in ecological protection and agricultural water resource management. Full article