Search Results (251)

Van der Waals (vdW) heterostructures are attractive for optoelectronic devices due to their lattice-mismatch tolerance and tunable band structures. Here, we report a gate-tunable Au/MoS₂/WSe₂ dual junction photodetector featuring competing asymmetric built-in electric fields. Spatially resolved photocurrent measurements reveal that selective utilization of these built-in electric fields decouples the transport dynamics of dark and photogenerated carriers. Such decoupling allows for independent modulation of the dark current and photocurrent, enabling the concurrent realization of the ultralow dark current and high photocurrent. Moreover, gate-voltage modulation enhances the photoresponse by ~245%, yielding a detectivity of 1.98 × 10¹² Jones over the 532–940 nm range. Imaging and optical communication further verify the device’s practical potential. These results provide a viable route toward high-sensitivity and electrically reconfigurable broadband photodetectors. Full article

Dynamic wireless power transfer can reduce electric vehicles’ charging downtime and range anxiety, but its benefits depend on route characteristics and system design. This work develops an integrated numerical framework combining (i) route-specific drive-cycle analysis, (ii) identification of candidate charging segments based on speed, stops and slope constraints, (iii) a physics-informed inductive wireless power transfer model and (iv) a Matlab/Simulink vehicle energy model to quantify energy demand, transferred energy and state-of-charge evolution. Two vehicle types (a passenger light-duty vehicle and a light commercial van) and multiple Lisbon Metropolitan Area routes are analyzed, including commuting, ride-hailing and urban logistics operations. Results show that low-speed, stop-rich urban corridors achieve the highest transfer rates (typically 0.4 kWh/km and over 2 kWh for more than 15 stops in the analyzed cases), whereas expressway deployments are much less effective (down to 0.1 kWh/km and 0.5 kWh below 5 stops) unless congestion lowers average speeds. The proposed workflow provides a replicable basis to identify candidate segments and to size wireless power transfer and corridor length for city-scale deployment scenarios. 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

Electric-field-sensitive dielectrics play a crucial role in electric field induction sensing and related capacitive conversion, with interfacial polarization and charge accumulation largely determining the signal output. This paper introduces graphene/transition metal dichalcogenide (TMD) (MoSe₂, MoS₂, and WS₂) heterojunctions as functional fillers to enhance the dielectric response and electric-field-induced voltage output of flexible polydimethylsiloxane (PDMS) composites. Density functional theory (DFT) calculations were used to evaluate the stability of the heterojunctions and interfacial electronic modulation, including binding behavior, charge redistribution, and Fermi level-referenced band structure/total density of states (TDOS) characteristics. The calculations show that the graphene/TMD interface is primarily controlled by van der Waals forces, exhibiting negative binding energy and significant interfacial charge rearrangement. Based on these theoretical results, graphene/TMD heterojunction powders were synthesized and incorporated into polydimethylsiloxane (PDMS). Structural characterization confirmed the presence of face-to-face interfacial contacts and consistent elemental co-localization within the heterojunction filler. Dielectric spectroscopy analysis revealed an overall improvement in the dielectric constant of the composite materials while maintaining a stable loss trend within the studied frequency range. More importantly, calibrated electric field induction tests (based on pure PDMS) showed a significant enhancement in the voltage response of all heterojunction composite materials, with the WS₂-G/PDMS system exhibiting the best performance, exhibiting an electric-field-induced voltage amplitude 7.607% higher than that of pure PDMS. This work establishes a microscopic-to-macroscopic correlation between interfacial electronic modulation and electric-field-sensitive dielectric properties, providing a feasible interface engineering strategy for high-performance flexible dielectric sensing materials. Full article

The van der Waals (vdW) interaction energy is a crucial factor in evaluating the potential destabilization of colloidal systems, such as those found in drinking-water treatment, where particles are often assumed to be spherical. Although the explicit dependence of the vdW interaction energy on the radii of spherical particles and their distances is known, a simple view is lacking due to the complexity of the relations. Here, we propose explicit, algebraically simple, approximate relations that provide insight into the fundamental influence of the input geometrical parameters. These relations, when combined with the exponentially decaying potential generated by the electrical double layer, can provide an approximate evaluation of the onset of raw water destabilization in drinking-water treatment, in other words, establishing the conditions under which pollutants in raw water begin to aggregate. Full article

Rural Sub-Saharan Africa (SSA) faces limited transport options, with many dispersed settlements dependent on poorly maintained roads. Light delivery vehicles (LDVs) can improve mobility, but conventional internal combustion engine vehicles are costly to operate and contribute to emissions. Electric vehicle (EV) conversions offer a practical alternative by extending vehicle life and reducing energy, maintenance, and environmental costs. This study presents a simulation-based framework to guide LDV conversion design for rural SSA. The framework includes component sizing, subsystem modeling, and full-vehicle benchmarking under representative conditions. Scenario-based simulations include trips ranging from shorter local access routes to longer remote trips on both paved and dirt roads, allowing the conversion’s performance to be quantified under representative conditions. A sensitivity analysis indicates that road grade, aerodynamic drag, and rolling resistance are the primary factors driving energy use variation. Using the Worldwide Harmonized Light Vehicles Test Procedure (WLTP) drive cycle, the conversion energy consumption (∼217 Wh/km) comparable to that of commercial electric vans, though the range is reduced relative to its battery capacity. The framework establishes a benchmark for EV conversion performance in SSA and supports broader adoption of sustainable rural mobility solutions. Full article

This study investigates the effect of laser power, focal length, and number of passes on the fabrication of graphene-based strain sensors using a 450 nm diode laser at the upper limit of the UV spectrum. Polyimide substrates were irradiated to produce laser-induced graphene, and the resulting sensors were evaluated under three-point bending tests. The main requirements for deformation sensors—adequate conductivity, mechanical stability under bending, and high sensitivity (gauge factor)—were assessed through morphological analysis by SEM, Raman spectroscopy, and electrical characterization using the Van der Pauw method. The results indicate that laser power is the critical factor influencing graphene quality and sensor performance, while focal length has a negligible effect and additional passes reduce material quality and sensitivity. Overall, this work demonstrates the feasibility of producing functional, low-cost graphene strain sensors with a commercial diode laser, offering a scalable and affordable alternative for sensor fabrication. Full article

Two-dimensional materials and their van der Waals heterostructures have shown great potential in quantum physics, flexible electronics, and optoelectronic devices. However, interfacial bubbles originated from trapped air, solvent residues, adsorbed molecules and reaction byproducts remain a key limitation to performance. This review provides a comprehensive overview of the formation mechanisms, characteristics, impacts, and optimization strategies related to bubbles in 2D heterostructures. We first summarize common fabrication approaches for constructing 2D heterostructures and discuss the mechanisms of bubble formation together with their physicochemical features. Then, we introduce characterization techniques ranging from macroscopic morphological observation to atomic-scale interfacial analysis, including optical microscopy, atomic force microscopy, transmission electron microscopy, and spectroscopic methods systematically. The effects of bubbles on the mechanical, electrical, thermal, and optical properties of 2D materials are subsequently examined. Finally, we compare key interface optimization strategies—such as thermal annealing, chemical treatments, AFM-based cleaning, electric field-driven approaches, clean assembly and AI-assisted methods. We demonstrate that, although substantial advances have been made in understanding interfacial bubbles, key fundamental challenges persist. Future breakthroughs will require the combined advancement of mechanistic insight, in situ characterization, and process engineering. Moreover, with the rapid adoption of AI and autonomous experimental platforms in materials fabrication and data analysis, AI-enabled process optimization and real-time characterization are emerging as key enablers for achieving high-cleanliness and scalable van der Waals heterostructures. Full article

It is well known that the space radiation environment, which has contributions from the trapped particles within the Van Allen belts, solar energetic particles (SEPs) and galactic cosmic rays (GCRs), directly influences space systems. These systems rely on complex and fragile electronic devices, whose performance can be degraded because of the action of the radiation and its related phenomena: single-event effects (SEEs), displacement damages (DDs) and total ionizing dose (TID). This could cause failures to arise through various mechanisms, ranging from parametric drift failures, such as leakage current and threshold voltage, among others, to destructive effects, like single-event burnout (SEB) or single-event latch-up (SEL). These failures in electronics affect the system’s reliability and its performance, which could compromise the mission’s success. Considering this, the main objective of the SRPROTEC project is to develop and validate new composite materials with better shielding performance against space radiation to increase the radiation tolerance of microelectronic devices encapsulated with these materials. For this purpose, three composites will be synthesized using a liquid epoxy resin filled with silica as a matrix mixed in different proportions, with a high-Z filler. The presence of low-Z elements from the high hydrogen content in the polymer and the presence of high-Z fillers are expected to produce a material with good radiation shielding properties. The developed materials will be exhaustively characterized, subjecting the three composites and control samples to rheological outgassing; gamma radiation shielding; and thermal, electrical, thermomechanical and moisture absorption, among other tests. Finally, the composite with the best performance will be selected and subjected to degradation tests (thermal cycling in vacuum, thermal cycling, thermal shock and relative humidity tests) to determine its suitability for space packaging applications. Full article

A novel and facile route for intercalating alkali-metal ions and ammonium ions into the layered mixed-ion compound tungsten oxychloride (WO₂Cl₂) has been developed using the iodide–triiodide redox couple as a mild redox-active reagent. Unlike traditional intercalation techniques employing highly reducing and air-sensitive reagents such as n-butyllithium, alkali triethylborohydride, and naphthalenide, the I⁻/I₃⁻ redox system operates at a moderate potential (0.536 V vs. SHE), enabling safer handling under ambient conditions without stringent inert-atmosphere requirements. This redox pair promotes the reduction of W⁶⁺ to W⁵⁺, thereby facilitating cation insertion into the van der Waal (vdW) gaps of WO₂Cl₂. This method uniquely enables ammonium ion intercalation into WO₂Cl₂, a first for this system. Intercalation was confirmed by X-ray diffraction, scanning electron microscopy (SEM/EDS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), with measured lattice expansion correlating well with Shannon ionic radii and coordinating environments. Electrical transport measurements reveal a transition from insulating WO₂Cl₂ to a semiconducting phase for K_0.5WO₂Cl₂, exhibiting a resistance drop of over four orders of magnitude. This work demonstrates the I⁻/I₃⁻ couple as a general, safe, and versatile method for layered mixed-anion materials, broadening the chemical toolkit for low-temperature, solution-based tuning of structures and properties. Full article

Passenger cars, sports utility vehicles (SUVs), and light trucks/vans, constituting the overwhelming majority of all road vehicles globally, burn about 25% of all fossil fuels, emit significant amounts of greenhouse gas emissions (CO₂), and deteriorate the environment. Nearly three-quarters of the engine power generated by burning fossil fuels is required to overcome aerodynamic resistance (drag) at highway driving speeds. Streamlining the body shape, especially the projected frontal area, can lead to a decrease in aerodynamic drag. Even though drag coefficients have plateaued since the late 1990s, further altering body shape might worsen vehicle cooling. Thus, the primary objective of this study is to explore the potential for aerodynamic drag reduction and improved cooling performance through careful component design unaffected by stylistic restraints. A variety of strategies for protecting the cooling intakes to reduce the drag coefficient are considered. The potential cooling drag reduction was found to be around 7% without compromising the cooling performance, which is in line with predictions for roughly 2.9% and 1.7% fuel consumption reductions for highway and city driving conditions, respectively. The study also reveals that passenger electric cars designed for city driving conditions possess a battery-to-kerb weight ratio of around one-quarter of the kerb weight, and vehicles designed for higher ranges have significantly higher ratios (nearly one-third), resulting in higher rolling resistance and energy consumption. The reduction of battery weight for EVs, streamlining vehicle shapes, and applying active and passive airflow management can help reduce aerodynamic drag and rolling resistance further, enhance driving range, and reduce energy consumption and greenhouse gas emissions. Full article

Tellurium–selenium alloy films exhibit excellent performance in short-wave infrared photodetection due to their adjustable bandgap, high carrier mobility, low fabrication temperature, and compatibility with CMOS technologies. Owing to their distinctive one-dimensional chain-like architecture, they can form van der Waals heterojunctions with materials such as silicon, III–V compound semiconductors, and metal oxides. This enables the construction of high-performance short-wave infrared photodetectors. This research examines the latest advancements in heterojunction photodetectors utilizing Te_xSe_1−x alloy sheets. First, the backdrop and justification of this review are outlined followed by discussing the fundamental aspects of Te_xSe_1−x alloy films including their appearance, electrical functionality, optoelectronic performance, fabrication methods and figures of merit for photodetectors. Subsequently, we examine recent advancements in heterojunction photodetectors based on Te_xSe_1−x alloy films and discuss methods to enhance device performance through interface engineering and structural design. Finally, we consolidate the findings and discuss potential future developments and challenges we may encounter. Full article

This work presents the results of a theoretical investigation of the electronic and optical properties of van der Waals Janus nanoheterostructures MoS₂/SeMoS and MoSe₂/SMoSe, carried out within the framework of density functional theory (DFT) using the generalized gradient approximation (GGA-PBE) together with the Grimme-D3 dispersion correction. The calculated band structures show that both heterostructures possess an indirect bandgap whose magnitude is highly sensitive to an external electric field. In the MoS₂–SeMoS system, increasing the applied field leads to a gradual narrowing of the bandgap and a transition to a metallic state at approximately 75 V, whereas in MoSe₂–SMoSe, the bandgap first increases (up to 20 V) and then decreases, indicating a nonlinear field-dependent behavior. Analysis of the dielectric function reveals an enhancement of the static dielectric permittivity and a red shift in the absorption spectra with increasing field strength, which can be attributed to charge redistribution and an increased contribution from ionic polarizability. These results demonstrate the possibility of effectively controlling the bandgap width, polarizability, and optical response of Janus nanoheterostructures using an external electric field. This opens up promising prospects for their application in tunable photodetectors, light modulators, valleytronic components, and next-generation optoelectronic systems. Full article

This study employs density functional theory (DFT) and time-dependent DFT (TD-DFT) to systematically investigate the ground- and excited-state properties of hybrid systems composed of CdSe quantum dots (QDs) with graphene and boron nitride (BN). Through Multiwfn wavefunction analysis, we calculated the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gaps and density of states (DOS), revealing distinct symmetry-dependent electronic characteristics. The HOMO–LUMO gap analysis demonstrates graphene’s superior charge transfer capability compared to BN, attributed to its higher structural symmetry enabling more efficient orbital overlap. DOS analysis further confirms the enhanced electrical conductivity in symmetry-matched graphene hybrids. The independent gradient model (IGM) and reduced density gradient (RDG) analyses reveal fundamentally different interfacial interaction patterns: the graphene hybrid exhibits uniform van der Waals interactions, consistent with its hexagonal symmetry, while the BN system shows heterogeneous interactions with localized hydrogen bonding due to symmetry reduction from heteroatomic composition. Binding energy calculations indicate greater stability in the graphene-based hybrid, reflecting optimal symmetry matching at the interface. UV–Vis spectra analysis shows that graphene dominates the optical response in its hybrid system, maintaining its symmetric spectral characteristics, while CdSe QDs govern the BN hybrid’s absorption. Electrostatic potential distributions remain essentially unchanged post-hybridization, preserving the intrinsic charge symmetry of components. Two-photon absorption (TPA) characterization reveals significant nonlinear optical properties in CdSe QDs, particularly at the first excited state. This work provides the first systematic comparison of charge transfer dynamics in CdSe QDs hybridized with graphene versus BN, demonstrating how material symmetry governs optoelectronic modulation mechanisms. The findings establish symmetry–property relationships that inform the design of low-dimensional hybrid materials for photonic applications. Full article

High-quality AZO thin films were produced on a 4-inch Si substrate using large-area PLD equipment at a substrate temperature of 330 °C, with a ZnO: Al (98:2 wt.%) target. This study aims to enhance the electrical, optical, morphological and structural properties of large-area PLD-grown AZO thin films by tuning the deposition pressures. The samples were prepared under high-vacuum (HV) conditions, as well as in oxygen atmospheres of 0.005 mbar O₂, 0.01 mbar O₂, and 0.1 mbar O₂. Consequently, a bilayer AZO film was prepared in a combination of two deposition pressures (first layer prepared under HV, followed by the second layer prepared at 0.01 mbar O₂). Additionally, morphological and structural characterization revealed that high-quality columnar growth AZO thin films free of droplets, with a strong (002) orientation, were achieved on a 4-inch Si substrate. Moreover, Hall measurements in the Van der Pauw configuration were used to assess the electrical properties. A low electrical resistivity of 3.98 × 10⁻⁴ Ω cm, combined with a high carrier concentration (n) of 1.05 × 10²¹ cm⁻³ and a charge carrier mobility of 17.9 cm²/V s, was achieved at room temperature for the sample prepared under HV conditions. The optical characterization conducted through spectroscopic ellipsometry measurements showed that the large-area AZO sample exhibits an increased optical transparency in the visible (VIS) range with a near-zero extinction coefficient (k) and a wide bandgap of 3.75 eV, fulfilling the standards for materials classified as TCO. In addition, the increased thickness uniformity of the prepared AZO films over a large area represents a significant step in scaling the PLD technique for industrial applications. Full article