Search Results (714)

Graphene’s exceptional carrier mobility and broadband absorption make it promising for ultrafast photodetection. However, its low optical absorption limits responsivity, while the absence of a bandgap results in high dark current, constraining the signal-to-noise ratio and efficiency. Although silicon (Si) photodetectors normally offer fabrication compatibility, their performance is severely hindered by interface trap states and optical shading. To overcome these limitations, we demonstrate an epitaxial graphene/n-Si heterojunction photodiode. This device utilizes graphene epitaxially grown on germanium integrated with a transferred Si thin film, eliminating polymer residues and interface defects common in transferred graphene. As a result, the fabricated photodetector achieves an ultralow dark current of 1.2 × 10⁻⁹ A, a high responsivity of 1430 A/W, and self-powered operation at room temperature. This work provides a strategy for high-sensitivity and low-power photodetection and demonstrates the practical integration potential of graphene/Si heterostructures for advanced optoelectronics. Full article

Addressing the challenges of bulky, low-efficiency sound-insulation materials at low frequencies, this work proposes an acoustic metamaterial based on curve fractal channels. Each unit cell comprises a concentric circular-ring channel recursively iterated: as the fractal order increases, the channel path length grows exponentially, enabling outstanding sound-insulation performance within a deep-subwavelength thickness. Finite-element and transfer-matrix analyses show that increasing the fractal order from one to three raises the number of bandgaps from three to five and expands total stop-band coverage from 17% to over 40% within a deep-subwavelength thickness. Four-microphone impedance-tube measurements on the third-order sample validate a peak transmission loss of 75 dB at 495 Hz, in excellent agreement with simulations. Compared to conventional zigzag and Hilbert-maze designs, this curve fractal architecture delivers enhanced low-frequency broadband insulation, structural lightweighting, and ease of fabrication, making it a promising solution for noise control in machine rooms, ducting systems, and traffic environments. The method proposed in this paper can be applied to noise reduction of transmission parts for ceramic automation production. Full article

With their superior switching speed, GaN high-electron-mobility transistors (HEMTs) enable high power density, reduce energy losses, and increase power efficiency in a wide range of applications, such as power electronics, due to their high breakdown voltage. GaN-HEMT devices are subject to long-term reliability due to the self-heating effect and lattice mismatch between the SiC substrate and the GaN. Depletion-mode GaN HEMTs are utilized for radio frequency applications, and this work investigates three wide-bandgap (WBG) GaN HEMT fixed-frequency oscillators with output buffers. The first GaN-on-SiC HEMT oscillator consists of an HEMT amplifier with an LC feedback network. With the supply voltage of 0.8 V, the single-ended GaN oscillator can generate a signal at 8.85 GHz, and it also supplies output power of 2.4 dBm with a buffer supply of 3.0 V. At 1 MHz frequency offset from the carrier, the phase noise is −124.8 dBc/Hz, and the figure of merit (FOM) of the oscillator is −199.8 dBc/Hz. After the previous study, the hot-carrier stressed RF performance of the GaN oscillator is studied, and the oscillator was subject to a drain supply of 8 V for a stressing step time equal to 30 min and measured at the supply voltage of 0.8 V after the step operation for performance benchmark. Stress study indicates the power oscillator with buffer is a good structure for a reliable structure by operating the oscillator core at low supply and the buffer at high supply. The second balanced oscillator can generate a differential signal. The feedback filter consists of a left-handed transmission-line LC network by cascading three unit cells. At a 1 MHz frequency offset from the carrier of 3.818 GHz, the phase noise is −131.73 dBc/Hz, and the FOM of the 2nd oscillator is −188.4 dBc/Hz. High supply voltage operation shows phase noise degradation. The third GaN cross-coupled VCO uses 8-shaped inductors. The VCO uses a pair of drain inductors to improve the Q-factor of the LC tank, and it uses 8-shaped inductors for magnetic coupling noise suppression. At the VCO-core supply of 1.3 V and high buffer supply, the FOM at 6.397 GHz is −190.09 dBc/Hz. This work enhances the design techniques for reliable GaN HEMT oscillators and knowledge to design high-performance circuits. Full article

In the present study, two novel donor–acceptor (D–A) conjugated copolymers, PIDTBDI and PIDTTBDI, were successfully synthesized via Stille coupling polymerization. These alternating copolymers incorporate indacenodithiophene and indacenodithienothiophene as donor units, coupled with benzothiadiazole dicarboxylic imide as the electron-deficient acceptor unit. The influence of extended conjugation on the structural, optical, thermal, and electrochemical properties of the copolymers was systematically investigated and confirmed by density functional theory (DFT). XRD analysis confirmed that both polymers are amorphous. Thermogravimetric analysis revealed that both materials possess excellent thermal stability, with decomposition temperatures exceeding 270 °C. The theoretical and experimental values of the energy gap confirmed the thermal stability of the studied polymers. The molecular weight was determined to be 10,673 Da for PIDTBDI and 7149 Da for PIDTTBDI. Despite the variation in molecular weight, both copolymers exhibited comparable optical and electrochemical bandgaps of approximately 1.57 and 1.69 eV, respectively. Electrochemical measurements showed that PIDTBDI has a HOMO energy level of −5.30 eV and a LUMO level of −3.61 eV, while PIDTTBDI displays HOMO and LUMO levels of −5.28 eV and −3.59 eV, respectively. These results indicate that minor structural differences can considerably affect the electronic characteristics of the polymers, thus altering their overall efficacy in solar cell applications. Full article

Over efficient photocatalysts, CO₂ photoreduction typically converts CO₂ into low-carbon chemicals, which serve as raw materials for downstream synthesis processes. Here, an efficient composite photocatalyst heterojunction (Cu₂O-u/g-C₃N₄) has been fabricated to reduce CO₂. Graphitic carbon nitride (g-C₃N₄) was synthesized via thermal polymerization of urea at 550 °C, while pre-dispersed Cu₂O derived from urea pyrolysis (Cu₂O-u) was prepared by thermal reduction of urea and CuCl₂·2H₂O at 180 °C. The heterojunction Cu₂O-u/g-C₃N₄ was subsequently constructed through hydrothermal treatment at 180 °C. This heterojunction exhibited a bandgap of 2.10 eV, with dual optical absorption edges at 485 nm and above 800 nm, enabling efficient harvesting of solar light. Under 175 W mercury lamp irradiation, the heterojunction catalyzed liquid-phase CO₂ photoreduction to formic acid, acetic acid, and methanol. Its formic acid production activity surpassed that of pristine g-C₃N₄ by 3.14-fold and TiO₂ by 8.72-fold. Reaction media, hole scavengers, and reaction duration modulated product selectivity. In acetonitrile/isopropanol systems, formic acid and acetic acid production reached 579.4 and 582.8 μmol·h⁻¹·g_cat⁻¹. Conversely, in water/triethanolamine systems, methanol production reached 3061.6 μmol·h⁻¹·g_cat⁻¹, with 94.79% of the initial conversion retained after three cycles. Finally, this work ends with the conclusions of the CO₂ photocatalytic reduction to formic acid, acetic acid, and methanol, and recommends prospects for future research. Full article

Automotive NVH (Noise, Vibration, and Harshness) performance significantly impacts driving comfort and traffic safety. Vehicles exhibiting superior NVH characteristics are more likely to achieve consumer acceptance and enhance their competitiveness in the marketplace. In the development of automotive NVH performance, traditional vibration reduction methods have proven to be mature and widely implemented. However, due to constraints related to size and weight, these methods typically address only high-frequency vibration control. Consequently, they struggle to effectively mitigate vehicle body and component vibration noise at frequencies below 200 Hz. In recent years, acoustic metamaterials (AMMs) have emerged as a promising solution for suppressing low-frequency vibrations. This development offers a novel approach for low-frequency vibration control. Nevertheless, conventional design methodologies for AMMs predominantly rely on empirical knowledge and necessitate continuous parameter adjustments to achieve desired bandgap characteristics—an endeavor that entails extensive calculations and considerable time investment. With advancements in machine learning technology, more efficient design strategies have become feasible. This paper presents a tandem neural network (TNN) specifically developed for the design of AMMs. The trained neural network is capable of deriving both the bandgap characteristics from the design parameters of AMMs as well as deducing requisite design parameters based on specified bandgap targets. Focusing on addressing low-frequency vibrations in the back frame of automobile seats, this method facilitates the determination of necessary AMMs design parameters. Experimental results demonstrate that this approach can effectively guide AMMs designs with both speed and accuracy, and the designed AMMs achieved an impressive vibration attenuation rate of 63.6%. Full article

A wide-bandgap AgInGaSe₂ (AIGS) thin film was fabricated using molecular beam epitaxy (MBE) via a three-stage method. The influence of Selenium (Se) pressure on the properties of AIGS films and solar cells was studied in detail. It was found that Se pressure played a very important role during the fabrication process, whereby Se pressure was varied from 0.8 × 10⁻³ Torr to 2.5 × 10⁻³ Torr in order to specify the effect of Se pressure. A two-stage mechanism during the production of AIGS solar cells was concluded according to the experimental results. With an increase in Se pressure, the grain size significantly increased due to the supply of the Ag–Se phase; the superficial roughness also increased. When Se pressure was increased to 2.1 × 10⁻³ Torr, the morphology of AIGS changed abruptly and clear grain boundaries were observed with a typical grain size of over 1.5 μm. AIGS films fabricated with a low Se pressure tended to show a higher bandgap due to the formation of anti-site defects such as In and Ga on Ag sites as a result of the insufficient Ag–Se phase. With an increase in Se pressure, the crystallinity of the AIGS film changed from the (220)-orientation to the (112)-orientation. When Se pressure was 2.1 × 10⁻³ Torr, the AIGS solar cell demonstrated its best performance of about 9.6% (Voc: 810.2 mV; Jsc: 16.7 mA/cm²; FF: 71.1%) with an area of 0.2 cm². Full article

Lead sulfide colloidal quantum dots (PbS QDs) have demonstrated great potential in short-wave infrared (SWIR) photodetectors due to their tunable bandgap, low cost, and broad spectral response. While significant progress has been made in surface ligand modification and defect state passivation, studies focusing on the interface between QDs and electrodes remain limited, which hinders further improvement in device performance. In this work, we propose an interface engineering strategy based on 3-aminopropyltriethoxysilane (APTES) to enhance the interfacial contact between PbS QD films and ITO interdigitated electrodes, thereby significantly boosting the overall performance of SWIR photodetectors. Experimental results demonstrate that the optimal 0.5 h APTES treatment duration significantly enhances responsivity by achieving balanced interface passivation and charge carrier transport. Moreover, The APTES-modified device exhibits a controllable dark current and faster photo-response under 1310 nm illumination. This interface engineering approach provides an effective pathway for the development of high-performance PbS QD-based SWIR photodetectors, with promising applications in infrared imaging, spectroscopy, and optical communication. Full article

Nonlinear characteristics are essential for neuromorphic devices to process high-dimensional and unstructured data. However, enabling a device to realize a nonlinear response under the same stimulation condition is challenging as this involves two opposing processes: simultaneous charge accumulation and recombination. In this study, a hybrid transistor based on a mixed-halide perovskite was fabricated to achieve dynamic nonlinear changes in synaptic plasticity. The utilization of a light-induced mixed-bandgap structure within the mixed perovskite film has been demonstrated to increase the recombination paths of photogenerated carriers of the hybrid film, thereby promoting the formation of nonlinear signals in the device. The constructed heterojunction optoelectronic synaptic transistor, formed by combining a mixed-halide perovskite with a p-type semiconductor, generates dynamic nonlinear decay responses under 400 nm light pulses with an intensity as low as 0.02 mW/cm². Furthermore, it has been demonstrated that nonlinear photocurrent growth can be achieved under 650 nm light pulses. It is important to note that this novel nonlinear response is characterized by its dynamism. These improvements provide a novel method for expanding the modulation capability of optoelectronic synaptic devices for synaptic plasticity. Full article

Group IV element-based topological semimetals (TSMs) are pivotal for next-generation quantum devices due to their ultra-high carrier mobility and low-energy consumption. However, germanium (Ge)-based TSMs remain underexplored despite their compatibility with existing semiconductor technologies. Here, we propose a novel I229-Ge₄₈ allotrope constructed via bottom-up cluster assembly that exhibits a unique porous spherical Fermi surface and strain-tunable topological robustness. First-principles calculations reveal that I229-Ge₄₈ is a topological nodal line semimetal with exceptional mechanical anisotropy (Young’s modulus ratio: 2.27) and ductility (B/G = 2.21, ν = 0.30). Remarkably, the topological property persists under spin-orbit coupling (SOC) and tensile strain, while compressive strain induces a semiconductor transition (bandgap: 0.29 eV). Furthermore, I229-Ge₄₈ demonstrates strong visible-light absorption (10⁵ cm⁻¹) and a strong strain-modulated infrared response, surpassing conventional Ge allotropes. These findings establish I229-Ge₄₈ as a multifunctional platform for strain-engineered nanoelectronics and optoelectronic devices. Full article

Dye-sensitized solar cells (DSSCs) are promising alternatives for power generation due to their environmental friendliness, cost effectiveness, and strong performance under diffused light. Conversely, their low spectral response in the ultraviolet (UV) region significantly obliterates their overall performance. The so-called luminescent down-shifting (LDS) presents a practical solution by converting high-energy UV photons into visible light that can be efficiently absorbed by sensitizer dyes. Herein, a conventional solid-state technique was applied for the synthesis of an LDS, europium (II)-doped barium orthosilicate (BaSiO₃:Eu²⁺) material. The material exhibited strong UV absorption, with prominent peaks near 400 nm and within the 200–300 nm range, despite a weaker response in the visible region. The estimated optical bandgap was 3.47 eV, making it well-suited for UV absorbers. Analysis of the energy transfer mechanism from the LDS material to the N719 dye sensitizer depicted a strong spectral overlap of $2\times {10}^{10}{\mathrm{M}}^{-1}{\mathrm{c}\mathrm{m}}^{-1}{\mathrm{n}\mathrm{m}}^4$, suggesting efficient energy transfer from the donor to the acceptor. The estimated Förster distance was approximately $6.83\mathrm{n}\mathrm{m}$, which matches the absorption profile of the dye-sensitizer. Our findings demonstrate the potential of BaSiO₃:Eu²⁺ as an effective LDS material for enhancing UV light absorption and improving DSSC performance through increased spectral utilization and reduced UV-induced degradation. Full article

The use of CH₄ as an energy source is increasing every day. To increase the efficiency of CH₄ combustion and ensure that the equipment meets ecological requirements, it is necessary to measure the CH₄ concentration in the exhaust gases of combustion systems. To this end, sensors are required that can withstand extreme operating conditions, including temperatures of at least 600 °C, as well as high pressure and gas flow rate. ZnGa₂O₄, being an ultra-wide bandgap semiconductor with high chemical and thermal stability, is a promising material for such sensors. The synthesis and investigation of the structural and CH₄ sensing properties of ceramic pellets made from pure and Er-doped ZnGa₂O₄ were conducted. Doping with Er leads to the formation of a secondary Er₃Ga₅O₁₂ phase and an increase in the active surface area. This structural change significantly enhanced the CH₄ response, demonstrating an 11.1-fold improvement at a concentration of 10⁴ ppm. At the optimal response temperature of 650 °C, the Er-doped ZnGa₂O₄ exhibited responses of 2.91 a.u. and 20.74 a.u. to 100 ppm and 10⁴ ppm of CH₄, respectively. The Er-doped material is notable for its broad dynamic range for CH₄ concentrations (from 100 to 20,000 ppm), low sensitivity to humidity variations within the 30–70% relative humidity range, and robust stability under cyclic gas exposure. In addition to CH₄, the sensitivity of Er-doped ZnGa₂O₄ to other gases at a temperature of 650 °C was investigated. The samples showed strong responses to C₂H₄, C₃H₈, C₄H₁₀, NO_2, and H₂, which, at gas concentrations of 100 ppm, were higher than the response to CH₄ by a factor of 2.41, 2.75, 3.09, 1.16, and 1.64, respectively. The study proposes a plausible mechanism explaining the sensing effect of Er-doped ZnGa₂O₄ and discusses its potential for developing high-temperature CH₄ sensors for applications such as combustion monitoring systems and determining the ideal fuel/air mixture. Full article

To address the challenges of cotton cellulose materials being susceptible to environmental humidity and pollutant erosion, a strategy for constructing superhydrophobic functional coatings with biomimetic micro–nano composite structures was proposed. Through surface silanization modification, diatomite (DEM) and Fe₃O₄ nanoparticles were functionalized with octyltriethoxysilane (OTS) to prepare superhydrophobic diatomite flakes (ODEM) and OFe₃O₄ nanoparticles. Following the multi-scale composite principle, ODEM and OFe₃O₄ nanoparticles were blended and crosslinked via the hydroxyl-initiated ring-opening polymerization of epoxy resin (EP), resulting in an EP/ODEM@OFe₃O₄ composite coating with hierarchical roughness. Microstructural characterization revealed that the micrometer-scale porous structure of ODEM and the nanoscale protrusions of OFe₃O₄ form a hierarchical micro–nano topography. The special topography combined with the low surface energy property leads to a contact angle of 158°. Additionally, the narrow bandgap semiconductor characteristic of OFe₃O₄ induces the localized surface plasmon resonance effect. This enables the coating to attain 80% light absorption across the 350–2500 nm spectrum, and rapidly heat to 45.8 °C within 60 s under 0.5 sun, thereby demonstrating excellent deicing performance. This work provides a theoretical foundation for developing environmentally tolerant superhydrophobic photothermal coatings, which exhibit significant application potential in the field of anti-icing and anti-fouling. Full article

LK-99, with chemical formula Pb_10−xCu_x(PO₄)₆O, was recently reported to be a room-temperature superconductor. While this claim has met with little support in a flurry of ensuing work, a variety of calculations (mostly based on density-functional theory) have demonstrated that the system possesses some unusual characteristics in the electronic structure, in particular flat bands. We have established previously that within DFT, the system is insulating with many characteristics resembling the classic cuprates, provided the structure is not constrained to the P3(143) symmetry nominally assigned to it. Here we describe the basic electronic structure of LK-99 within self-consistent many-body perturbative approach, quasiparticle self-consistent GW (QSGW) approximation and their diagrammatic extensions. QSGW predicts that pristine LK-99 is indeed a Mott/charge transfer insulator, with a bandgap gap in excess of 3 eV, whether or not constrained to the P3(143) symmetry. When Pb₉Cu(PO₄)₆O is hole-doped, the valence bands modify only slightly, and a hole pocket appears. However, two solutions emerge: a high-moment solution with the Cu local moment aligned parallel to neighbors, and a low-moment solution with Cu aligned antiparallel to its environment. In the electron-doped case the conduction band structure changes significantly: states of mostly Pb character merge with the formerly dispersionless Cu d state, and high-spin and low spin solutions once again appear. Thus we conclude that with suitable doping, the ground state of the system is not adequately described by a band picture, and that strong correlations are likely. Irrespective of whether this system class hosts superconductivity or not, the transition of Pb₁₀(PO₄)₆O from being a band insulator to Pb₉Cu(PO₄)₆O, a Mott insulator, and multi-determinantal nature of doped Mott physics make this an extremely interesting case-study for strongly correlated many-body physics. Full article

Micro gas turbines serve small-scale generation where swift response and low emissions are highly valued, and they are commonly fuelled by natural gas. True to their ‘micro’ designation, their size is indeed compact; however, a noteworthy portion of the enclosure is devoted to power electronics components. This article considers whether these components can be made even smaller by substituting their conventional silicon switches with switches fashioned from silicon carbide. The wider bandgap of silicon carbide permits stronger electric fields and reliable operation at higher temperatures, which together promise lower switching losses, less heat, and simpler cooling arrangements. This study rests on a simple volumetric model. Two data sets feed the model. First come the manufacturer specifications for a pair of converter modules (one silicon, the other silicon carbide) with identical operation ratings. Second are the operating data and dimensions of a commercial 100 kW micro gas turbine. The model splits the converter into two parts: the semiconductor package and its cooling hardware. It then applies scaling factors that capture the higher density of silicon carbide and its lower switching losses. Lower switching losses reduce generated heat, so heatsinks, fans, or coolant channels can be slimmer. Together these effects shrink the cooling section and, therefore, the entire converter. The findings show that a micro gas turbine inverter built with silicon carbide occupies about one fifth less space and delivers more than a quarter higher power density than its silicon counterpart. Full article