Electron Trapping Research Articles

Defects Calculation and Accelerated Interfacial Charge Transfer in a Photoactive MOF-Based Heterojunction.

Photocatalytic hydrogen production is currently considered a clean and sustainable route to meet the energy and environmental issues. Among, heterojunction photocatalysts have been developed to improve their photocatalytic efficiency. Defect engineering of heterojunction photocatalysts is attractive due to it can perform as electron trap and change the band structure to optimize the interfacial separation rate of photogenerated electron-hole pairs. Here, the MOF-based heterojunction photocatalysts with theoretically high reduction and oxidation abilities are successfully synthesized, denoted ZrO2/Pt/Zr-MOF-X, with tuned linker defectivity through an in situ electrochemical route. The defectivity are rationally calculated from the TG and 1H NMR results. A positive correlation is found between the defectivity and photocatalytic activity, and ZrO2/Pt/Zr-MOF-6 with the optimized defectivity of ca. 35% exhibits the highest hydrogen production rate of up to 2923 µmol g-1 h-1, illustrating the importance of structural defects in heterojunction photocatalysts. Ultrafast transient absorption spectroscopy and electron spin resonance results unveil the highest carrier concentration and charge separation efficiency in the defected heterostructure of ZrO2/Pt/Zr-MOF-6 through a direct Z-scheme contact, leading to its efficient photocatalysis through the high redox power.

Integrated analysis of cellulose structure and properties using solid-state low-field H-NMR and photoacoustic spectroscopy

In this study, we explore the structural intricacies of cellulose, a polymer composed of glucose monomers arranged in a linear chain, primarily investigated through solid-state NMR techniques. Specifically, we employ low-field proton nuclear magnetic resonance (H-NMR) to delve into the diverse hydrogen atom types within the cellulose molecule. The low-field H-NMR technique allows us to discern these hydrogen atoms based on their distinct chemical shifts, providing valuable insights into the various functional groups present in cellulose. Our focus extends to the examination of anomeric protons of glucose units and protons linked to carbon atoms engaged in glycosidic linkages within cellulose chains, which exist in diverse crystalline and amorphous forms. Solid-state low-field H-NMR spectroscopy aids in characterizing the crystallinity degrees and amorphous regions within cellulose, revealing time-dependent changes in free induction decay (FID) signals. Complementing this, we investigate the photo-absorption properties of cellulose fibers under both continuous and modulated irradiation using reversed double-beam photoacoustic spectroscopy (RDB-PAS). This photoacoustic approach allows us to observe ultraviolet- and visible light-induced processes, including electron trap filling and reductive changes on the fiber surface. Our findings suggest that RDB-PAS is a feasible method for estimating the electron trap distribution, serving as a potential measure of the density of crystalline cellulose defects. This integrated approach of combining solid-state low-field H-NMR and RDB-PAS techniques offers a comprehensive understanding of cellulose structure and properties, enhancing our ability to characterize its diverse features.

Modeling of Composition and Channel Length-Dependent Transient Characteristics in Short-Channel IGZO Field-Effect Transistors.

In this study, we analyze the characteristics of fast transient drain current (ID) in IGZO-based field-effect transistors (FETs) with different composition ratios (device O: ratio of 1:1:1 for In, Ga, Zn, device G: ratio of 0.307:0.39:0.303) for reliable operations. Overshoot currents, which can cause device degradation, are caused by fast transients and are attributed to the trapping of electrons in the energy band. As the lateral electric field (Elat) of the IGZO channel is increased, the overshoot drain current difference (ΔIOS) is increased for both devices. It is also found that the increase in ΔIOS with decreasing L is less pronounced in device G compared with that for device O. While device G yields larger ΔIOS values than device O in long channels (L = 5, 10 μm), it yields smaller ΔIOS in short channels (L = 0.5, 1 μm). This phenomenon is explained using three physical parameters (nOS, Ever, and NOT), based on Technology Computer-Aided Design (TCAD) simulation modeling. Device G has stronger immunity against ΔIOS in a short-channel region; this can be attributed to the lower concentration of oxygen vacancies in device G that suppresses dopant diffusion effects within IGZO layer. These results experimentally demonstrate that the short-channel effects on fast-transient ID can be improved by controlling the Ga composition ratio of IGZO.

Defect-mediated electron–phonon coupling in halide double perovskite

Optically active defects often play a crucial role in governing the light emission as well as the electronic properties of materials. Moreover, defect-mediated states in the midgap region can trap electrons, thus opening a path for the recombination of electrons and holes in lower energy states that may require phonons in the process. Considering this, we have probed electron–phonon interaction in halide perovskite systems with the introduction of defects and investigated the thermal effect on this interaction. Here, we report Raman spectroscopic study of the thermal evolution of electron–phonon coupling, which is tunable with the crystal growth conditions, in the halide perovskite systems Cs2AgInCl6 and Cs2NaInCl6. The signature of electron–phonon coupling is observed as a Fano anomaly in the lowest frequency phonon mode (51 cm−1), which evolves with temperature. In addition, we observe a broad band in the photoluminescence (PL) measurements for the defect-mediated systems, which is otherwise absent in defect-free halide perovskite. The simultaneous observation of the Fano anomaly in the Raman spectrum and the emergence of the PL band suggests the defect-mediated midgap states and the consequent existence of electron–phonon coupling in the double perovskite.

Structural modification of defective WO3 by g-C3N4 for photocatalytic gold recovery from non-cyanide-based plating effluent

A set of nCN/WO3 − x composites was synthesized through a simple thermal treatment for gold recovery from the simulated effluent of a non-cyanide-based plating bath. The obtained results exhibited that all nCN/WO3 − x composites demonstrated a higher photocatalytic activity for gold recovery than their pristine components due to the formation of nanocomposites which paved a convenient pathway for charge transfer. Among all synthesized composites, the 5.0CN/WO3 − x composite exhibited the highest photocatalytic activity, recovering around 69.4% of gold within 120 min under UV-vis light irradiation at an intensity of 3.45 mW/cm² and a catalyst loading of 1.0 g/L, in the absence of hole scavenger. This result can be ascribed to the presence of an optimal number of defects, which can act as electron trapping sites and thereby reduce the recombination rate of charge carriers. Gold recovery increased with repeated reuse, attributed to the decorated gold, which enhances light absorption and decreases the recombination rate of charge carriers. The feasible application of used CN/WO3 − x were also explored for H2 production, dye degradation and gold recovery. The obtained results provide a new insight about the photocatalytic recovery of gold from industrial wastewater and also shed light on the application of gold-decorated CN/WO3 − x as a catalyst for other photocatalytic applications.

Suppressing Polaronic Defect-Photocarrier Interaction in Halide Perovskites by Pre-distorting Its Lattice.

In halide perovskites, photocarriers can have strong polaronic interactions with point defects. For iodide-deficient MAPbI3, we found that the Fermi level can shift significantly by 0.6-0.7 eV upon light illumination. This energy level shift is accompanied by the formation of deep electron traps. These experimental observations are consistent with the formation of a Pb-Pb dimer when photoexcited electrons are trapped at an iodide vacancy. Interestingly, we found that this polaronic interaction is suppressed when a portion of MA+ cations is replaced by smaller Cs+ ions. Density functional theory calculations reveal that Cs-doping can reduce the distance between two Pb atoms across an iodide vacancy, even without electron trapping. The predistortion of the lattice induced by cation replacement resembles the Pb-Pb dimer formed by electron trapping at the defect site, which explains the suppression of light-induced effects observed in the experiment. Our finding unveils a counterintuitive strategy to enhance the photostability of halide perovskites by preintroducing distortions into its lattice.

Terahertz Saturable Absorption across Charge Separation in Photoexcited Monolayer Graphene/MoS2 Heterostructure.

Unveiling the nonlinear interactions between terahertz (THz) electromagnetic waves and free carriers in two-dimensional materials is crucial for the development of high-field and high-frequency electronic devices. Herein, we investigate THz nonlinear transport dynamics in a monolayer graphene/MoS2 heterostructure using time-resolved THz spectroscopy with intense THz pulses as the probe. Following ultrafast photoexcitation, the interfacial charge transfer establishes a nonequilibrium carrier redistribution, leaving free holes in the graphene and trapping electrons in the MoS2. When probed with intense THz pulses exceeding 34 kV/cm in a peak electric field, significant THz saturable absorption is observed over a period of 20 ps. Furthermore, the photoinduced change in the transmitted THz waveform, linked to the THz-driven nonlinear current, manifests as a substantial self-phase modulation. These nonlinear responses can be attributed to the competition between rapid carrier heating and slow carrier cooling via electron-electron and electron-phonon scattering in the charge-transfer-induced hole system of the graphene layer. This work demonstrates an integration of advantages arising from robust nonlinear absorption in graphene and enhanced photocarrier harvesting in transition metal dichalcogenides by exploiting heterostructure construction.

Fabrication of shaddock peel biochar mediated Cd0.8Zn0.2S nanocomposite and synergistic adsorptive-photocatalytic performance for pollutant removal

Developing inexpensive, eco-friendly and efficient catalysts is the key to photocatalytic removal of organic pollutants from wastewater. In this paper, a novel pre-treatment activated shaddock peel biochar mediated hexagonal Cd0.8Zn0.2S composite photocatalyst (CZS/BC) was fabricated by hydrothermal method and comprehensively characterized. The photocatalytic performance was assessed by degradation of Rhodamine B (RhB) in aqueous solution under visible light irradiation. Compared with the pristine Cd0.8Zn0.2S (CZS), the doping of shaddock peel biochar (BC) not only significantly reduces the band gap energy (Eg) of the CZS, but also significantly improves the adsorption and photocatalytic performance. Under the synergistic action of adsorption and photocatalysis, the optimal CZS/BC-0.3 sample exhibited the best removal performance, and could almost completely eliminate RhB pollutant within 50min with good stability, possessing great application potential in practical environmental remediation. The removal efficiency was 6.4 folds higher than pristine CZS. Studies on photocatalytic mechanism showed that photocatalysis was mainly predominated by •O2- and h+ induced pathways, and the enhancement of photocatalytic performance can be attributed to the formation of hexagonal CZS, with biochar as an electron bridge and trap, the photogenerated carrier can be separated more effectively, thus enhancing the photocatalytic performance. This work provides a new idea for constructing new composite photocatalysts using BC as electron transport bridge.

One-step fabrication of high energy storage polymer films with a wide bandgap and high melting temperature induced by the fluorine effect for high temperature capacitor applications with ultra-high efficiency.

The development of polymer dielectrics with both high energy density and low energy loss is a formidable challenge in the area of high-temperature dielectric energy storage. To address this challenge, a class of polymers (Parylene F) are designed by alternating fluorinated aromatic rings and vinyl groups in the polymer chain to confine the conjugating sequence and broaden the bandgap with the fluorine effect. The target films with desired thickness, ultra-high purity, and a wide bandgap are facilely fabricated by a one-step chemical vapor deposition (CVD) technique from monomers. The symmetric and bulky aromatic structures exhibit high crystalline performance and excellent stability at high temperature. The presence of strongly electronegative fluorine atoms effectively enhances bandgap and electron trapping capability, which effectively reduces the conduction loss as well as the possibility of breakdown at high temperatures. CVD technology avoids the post-processing film-forming process, ensuring the fabrication of thin films with high quality. These benefits allow Parylene F films to effectively store electrical energy at temperature up to 150 °C, exhibiting a record discharged energy density of 2.92 J cm-3 at charge-discharge efficiency exceeding 90%. This work provides a new idea for the design and synthesis of all-organic polymer dielectric films for high temperature applications.

Surfactants govern the fabrication of sulfur-enriched heterojunction catalysts for highly selective photocatalytic conversion of toluene

Photocatalytic selective oxidation of toluene represents a milder and more environmentally friendly strategy for the synthesis of benzaldehyde. In order to enhance catalytic performance, efficient carrier separation and transport are crucial in the photocatalytic process. This study focused on the preparation of ZnS@ZnIn2S4 with sulfur vacancies and heterostructures, combining the advantages properties of ZnS and ZnIn2S4 in photocatalysis. The effects of ZnS and surfactants on the catalytic properties of the composites were studied in depth. Characterization tests revealed that surfactant-modified ZnS@ZnIn2S4 exhibited a higher concentration of sulfur defects, which facilitated electron trapping and promoted photogenerated carrier separation and utilization. Additionally, the present study also demonstrated that the incorporation of ZnS and surfactants could reduce the crystal size of ZnIn2S4, thereby facilitating the exposure of additional active sites. The synergistic effect of the aforementioned advantages enabled toluene to undergo oxidation at a conversion rate of 39% in the presence of oxygen, resulting in the production of benzaldehyde with an exceptional selectivity of 92%. This finding offers valuable insights for future endeavors in designing photocatalytic C-H bond oxidation catalysts.

Ultrahigh detectivity of near-infrared organic phototransistor assisted by additional electron trap sites in a dielectric layer

This study introduced an additional electronic traps (ZnO nanoparticles) into the dielectric layer of the organic phototransistor, obtaining a high Ilight/Idark and an ultra-high detectivity while keeping the response time unchanged.

Stabilizing Electron Transport of 2D Materials.

2D materials are promising candidates for beyond-Si electronic devices. However, their stability is a key bottleneck in their industrial applications. The instability of 2D materials is mainly attributed to their intrinsic susceptibility to O2 and H2O-particularly to reactive oxygen species (ROS), which have strong oxidizing properties. Inspired by the antioxidant effect of vitamin C (VC) in organisms, a strategy based on the use of VC to stabilize electron transport in 2D materials is developed, which significantly improves the performance and stability of these materials and devices. The mobility is increased by more than an order of magnitude, and excellent performance of the device is maintained in air for >327 days, which is the best reported stability for MoS2 field-effect transistors to date. VC scavenges existing ROS via oxidation reactions and inhibits the generation of ROS by shielding excitons from oxygen quenching, which provides 2D materials lasting protection from electron trapping and oxidative damage, stabilizing electron transport. This approach, which is based on the simple utilization of readily available VC, has considerable potential for large-scale applications in the 2D material electronics industry.

Interfacial Electronic Charge Trapping and Photonic Carrier Excitation Coupling in Solution-Processed Zinc-Tin Oxide Thin-Film Transistors Applied for Logic Gate Design and Quantized Neural Network.

Components needed in Artificial Intelligence with a higher information capacity are critically needed and have garnered significant attention at the forefront of information technology. This study utilizes solution-processed zinc-tin oxide (ZTO) thin-film phototransistors and modulates the values of VG, which allows for the regulation of electron trapping/detrapping at the ZTO/SiO2 interface. By coupling the excited photonic carrier and electronic trapping, logic gates such as "AND," "OR," "NAND," and "NOR" can be achieved. With the exponential growth in data generation, efficient processing and storage solutions are imperative. However, extensive data transfer between computing units and storage limits the level of artificial neural networks (ANNs). Consequently, quantized neural networks (QNNs) have gained interest for their reduced computational resource requirements and lower consumption. In this context, we introduce an optimized ternary logic circuit based on ZTO devices. By utilizing optical modulation to adjust the turn-on voltage of the single device, we demonstrate the achievement of ternary current states, thereby providing three distinct discrete states. This configuration can be extended to QNN computing, demonstrating multilevel quantized current values for in-memory computation. We achieved a handwriting digit recognition rate of 91.6%, thereby demonstrating reliable QNN hardware performance. This robust QNN performance indicates that the metal oxide phototransistor shows significant potential for future ternary computing systems.

Decreased Secondary Electron Emission from Aluminum Surface by a Fluorocarbon-Titanium Composite Film.

Multipactor, a vacuum discharge under microwave conditions triggered by secondary electron emission (SEE), plays a critical role in managing the power level of microwave devices. In this study, we developed a fluorocarbon-titanium composite film on aluminum by cosputtering polytetrafluoroethylene (PTFE) and titanium via a controlled temperature and sputtering power ratio (RF power for PTFE to DC power for Ti) to suppress the SEE of Al. The evolution of microtopography and chemical composition of the composite film was evaluated. An increasing power ratio varying from 0.5 to 3.0 is found to change the film surface from scattered island-like bumps to a prominent peak-valley pattern and eventually to a smooth surface with few flat swellings. Elemental analysis revealed that the fluorine-to-carbon (F/C) mole ratio in samples was more significantly influenced by the sputtering power ratio than by the substrate temperature. The SEE yield indicates that the peak-valley pattern prepared by a power ratio of 2 leads to the maximum of the SEE yield curve reducing steeply from 2.99 to 1.23, which is attributed not only to the roughed pattern but also to the high F/C mole ratio owing to the higher capacity of electron trapping by the fluorine atoms.

Probing electron trapping by current collapse in GaN/AlGaN FETs utilizing quantum transport characteristics

GaN is expected to be a key material for next-generation electronics due to its interesting properties. However, current collapse poses a challenge to the application of GaN FETs to electronic devices. In this study, we investigate the formation of quantum dots in GaN FETs under current collapse. By comparing the Coulomb diamond between standard measurements and those under current collapse, we find that the gate capacitance is significantly decreased under current collapse. This suggests that the current collapse changes the distribution of trapped electrons at the device surface, as reported in the previous study by operando x-ray spectroscopy. In addition, we show external control of quantum dot formation, previously challenging in an FET structure, by using current collapse.

Impact of electron trapping on stimulated Raman scattering under incoherent broadband laser light in homogeneous plasma

Impact of electron trapping on stimulated Raman scattering under incoherent broadband laser light in homogeneous plasma

Ion-acoustic Shock and Solitary Waves in Magnetized Plasma with Cairns-Gurevich Distribution Electrons

Abstract The propagation properties of ion-acoustic solitary and shock waves in the magnetized viscous plasma with nonthermal trapped electrons are investigated. The Cairns-Gurevich distribution as the electron distribution is considered to describe the plasma nonthermality and particle trapping. By adopting the reductive perturbation technique, we derived the nonlinear Schamel-Korteweg–de Vries-Burgers (SKdVB) equation, and then obtained the ion-acoustic shock and solitary wave solutions of the SKdVB equation for different limiting cases. It is found that the impact of nonthermal parameter α, external magnetic field Ω, obliqueness lz, wave speed U0, and the ion kinematic viscosity η0 can significantly change the characteristics of the shock and solitary waves. These results may be useful for better understanding the propagation of nonlinear structures in space and laboratory plasma with nonthermal trapped electrons.

Trivalent Ionic Molecular Bridges as Efficient Charge-Trapping Method for All-Solid-State Organic Synaptic Transistors toward Neuromorphic Signal Processing Applications.

Achieving high retention of memory state is crucial in artificial synapse devices for neuromorphic computing systems. Of various memorizing methods, a charge-trapping method provides fast response times when it comes to the smallest size of electrons. Here, for the first time, it is demonstrated that trivalent molecular bridges with three ionic bond sites in the polymeric films can efficiently trap electrons in the organic synaptic transistors (OSTRs). A water-soluble polymer with sulfonic acid groups, poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA), is reacted with melamine (ML) to make trivalent molecular bridges with three ionic bond sites for the application of charge-trapping and gate-insulating layer in all-solid-state OSTRs. The OSTRs with the PAMPSA:ML layers are operated at low voltages (≤5V) with pronounced hysteresis and high memory retention characteristics (ML = 25 mol%) and delivered excellent potentiation/depression performances under modulation of gate pulse frequency. The optimized OSTRs could successfully process analog (Morse/Braile) signals to synaptic current datasets for recognition/prediction logics with an accuracy of >95%, supporting strong potential as all-solid-state synaptic devices for neuromorphic systems in artificial intelligence applications.

Study of Nanocomposites Based on Organoclay‐Filled Polypropylene/Poly(Butylene Succinate) Blends With Improved Electrical Properties

ABSTRACTThis study explores the behavior of the polypropylene/polybutylene succinate (PP*/PBS) polymer blend and its nanocomposites containing varying amounts of organically modified montmorillonite (OMMT) (Cloisite20: C20) (1%, 2%, 3%, 5%, and 10%) when subjected to electron beam irradiation in a scanning electron microscope (SEM). More specifically, we have studied the electrical properties of nanocomposites, in particular the trapping and transport of electrons in the material, as well as the emission of electrons. To examine the storage and spreading of injected electrical charge in nanocomposites under electron irradiation, we used time‐resolved current analysis method by measuring the induced currents (displacement and leakage currents). In order to verify whether there is a link between the electrical properties and the dispersion of the nanoclay particles in the polymer matrix, structural analyses were also carried out by x‐ray diffraction (XRD). The results revealed a significant increase in the equilibrium trapped charge as the amount of clay nanoparticles introduced into the matrix increased. This trend can be attributed to both an increase in the number of involved traps and the presence of interfaces that act as defect sites. This was checked by determining the energy distribution of the traps using Simmons' approach. Correlating the measured displacement and leakage currents allowed us to demonstrate that the presence of clay nanoparticles leads to a decrease in the electron emission efficiency.

Green preparation of nitrogen vacancies enriched g-C3N4 for efficient photocatalytic reduction of CO2 and Cr(VI)

Introducing vacancies has emerged as one of the valid strategies to modulate the photocatalytic performance of graphitic carbon nitride (g-C3N4). Introduction of nitrogen vacancies into g-C3N4 can create defect energy levels and trap electrons, consequently accelerating the separation of e−/h+ pairs and effectively boosting photocatalytic activity. Nitrogen vacancies can also serve as adsorption active sites, enhancing the adsorption capacity of the catalyst towards the target molecule (CO2). In this study, a series of g-C3N4 with abundant nitrogen vacancies were prepared using a green and facile strategy using sodium bisulfite treatment. Successful introduction of nitrogen vacancies endows with the photocatalyst more active sites, optimizes the band structure, significantly boosts the separation of photoexcited carriers, thereby remarkably enhancing photocatalytic CO2 and Cr(VI) reduction. On the 11CN photocatalyst (0.5 g g-C3N4 was treated by 11 g sodium bisulfite), the generation rate of CO and CH4 is 5.74 μmol·g−1·h−1 and 1.30 μmol·g−1·h−1, respectively, which is 3.19 times and 8.29 times higher than those on the reference g-C3N4 (CO: 1.37 μmol·g−1·h−1, CH4: 0.14 μmol·g−1·h−1). Under irradiation by three distinct monochromatic lights, the apparent quantum yield (AQY) of 11CN is also superior to that of the reference g-C3N4. Moreover, photocatalytic Cr(VI) reduction experiments were performed on the catalysts to demonstrate the universality of the catalysts The results show that the photocatalytic reduction rate constant of Cr(VI) by 11CN is 1.79 times higher than that over the reference g-C3N4. Stability of the catalyst was verified through cycling experiments, and the samples exhibit promising practical application prospect. The mechanism of photocatalytic CO2 reduction and the transformation pathway of intermediate products were elucidated using in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This study introduces a new strategy of introducing nitrogen vacancies into g-C3N4-based photocatalytic materials, providing an effective approach to enhance the photocatalytic activity of g-C3N4 in photocatalytic CO2 and Cr(VI) reduction.