Charge Accumulation Process Research Articles

Modeling of semiconductor heterostructures for energy converters and sensors

A set of modeling programs for constructing a sequence of energy zones of heterojunctions is presented for analyzing the distribution of charge carriers in the heterostructure and internal characteristics, for describing the processes of charge transfer and accumulation. Wolfram Mathematica analytical system and Delphi programming language were used. The main elements of materials are semiconductors, metals of contact structures and injection regions of nonequilibrium carriers. The programs allow determining the structural characteristics of materials, active zones and spatial charge regions, calculating quasi-Fermi levels and built-in potentials, as well as the efficiency of heterostructures in general and for separation-charge collection, charge accumulation, determining the type of metallization of barrier or ohmic contact.

Characteristics of Surface Charge Accumulation on Spacers and Its Influencing Factors

Charge accumulation usually happens on the surface of spacers under DC operation, which is susceptible to inducing surface flashover. In order to explore the surface charge accumulation mechanisms and the influences of dielectric conductivity, gas ion mobility, and temperature field on the surface charges, a time-varying charge density model at the gas–solid interface of spacers was established. The results of the simulation show that the discontinuity of the current density between the spacer bulk side and the gas ion flow is the fundamental reason for the charge accumulation on the spacer surface. Additionally, the value of current density fluxes at the interface continues to decrease with the change of the electric field, and the progress of charge transfer gradually stabilizes. Moreover, the dielectric conductivity directly affects the charge accumulation process, and there is a critical conductivity in which the effect of charge conduction in dielectrics counteracts that of gas-phase charge deposition, theoretically. When the conductivity is higher than the critical conductivity, the solid-side charge conduction is the main source of the surface charge accumulation, while the gas-phase charge deposition on the gas side plays a dominant role when the conductivity is lower than the critical conductivity. The charge accumulation is not significantly affected by gas ion mobility when the temperature is evenly distributed. However, under the temperature field with gradient distribution, the current density fluxes at the interface change, causing the polarity reverse of the accumulated charge. In the high-temperature region, the volume current density surges simultaneously with the conductivity, leading to a higher density of surface charge accumulation. Lastly, the design of spacers needs to keep the current densities on both sides of the interface as similar as possible in order to avoid excessive charge gathering in localized areas.

Thermodynamic driving forces in contact electrification between polymeric materials

Contact electrification, or contact charging, refers to the process of static charge accumulation after rubbing, or even simple touching, of two materials. Despite its relevance in static electricity, various natural phenomena, and numerous technologies, contact charging remains poorly understood. For insulating materials, even the species of charge carrier may be unknown, and the direction of charge-transfer lacks firm molecular-level explanation. Here, we use all-atom molecular dynamics simulations to investigate whether thermodynamics can explain contact charging between insulating polymers. Based on prior work suggesting that water-ions, such as hydronium and hydroxide ions, are potential charge carriers, we predict preferred directions of charge-transfer between polymer surfaces according to the free energy of water-ions within water droplets on such surfaces. Broad agreement between our predictions and experimental triboelectric series indicate that thermodynamically driven ion-transfer likely influences contact charging of polymers. Furthermore, simulation analyses reveal how specific interactions of water and water-ions proximate to the polymer-water interface explain observed trends. This study establishes relevance of thermodynamic driving forces in contact charging of insulators with new evidence informed by molecular-level interactions. These insights have direct implications for future mechanistic studies and applications of contact charging involving polymeric materials.

Dielectric multilayers impact on radiation-induced charge accumulation in highly sensitive oxide field effect transistors

Radiation dosimetry is crucial in many fields where the exposure to ionizing radiation must be precisely controlled to avoid health and environmental safety issues. Among solid state detectors, we recently demonstrated that Radiation sensitive OXide Field Effect Transistors (ROXFETs) are excellent candidates for personal dosimetry thanks to their fast response and high sensitivity to x rays. These transistors use indium–gallium–zinc oxide as a semiconductor, combined with a dielectric based on high-permittivity and high-atomic number materials. Here, we present a study on the ROXFET gate dielectric fabricated by atomic layer deposition, where we compare single- and multi-layer structures to determine the best-performing configuration. All the devices show stable operational parameters and high reproducibility among different detectors. We identified an optimized bi-layer dielectric structure made of tantalum oxide and aluminum oxide, which demonstrated a sensitivity of (63 ± 2) V/Gy, an order of magnitude larger than previously reported values. To explain our findings, we propose a model identifying the relevant charge accumulation and recombination processes leading to the large observed transistor threshold voltage shift under ionizing radiation, i.e., of the parameter that directly defines the sensitivity of the device.

Insights into the Interfacial Charge Transfer Dynamics in Semiconductor–Molecular Catalyst Assemblies for Photo–Induced CO2 Reduction

AbstractThis mini–review summarises examples of photo and photoelectrochemical CO2 reduction reactions (CO2RR) using semiconductor–molecular catalyst–based hybrid assemblies in which studies of charge transfer dynamics were also performed. In these catalysts, the grand challenges are controlling ultra–fast one–electron charge separation and simultaneously governing its impact on the efficiency and product selectivity in the multielectron and multi–proton–assisted CO2RR. In practice, several unwanted electron recombination processes occur in the femtosecond to millisecond timescale range impacting the overall catalysis efficiency. Titanium di‐oxide (TiO2) nanoparticle, mesoporous TiO2 film, copper indium sulphide (CuInS2) quantum dots were used as semiconductor materials, in turn rhenium (I) bipyridine, cobalt (II) terpyridine, cobaloxamine complex, and iron (III) porphyrins were investigated as molecular catalysts. The results of the charge transfer dynamic studies operating in such hybrid systems shed light on their charge accumulation processes, their rate constants for the intramolecular charge transfer processes and the decay lifetimes of the different excited state species that are produced. Moreover, a comprehensive understanding of the catalysts’ charge transfer dynamics is crucial to identifying detrimental charge recombination pathways. These undesired pathways can be used as rational basis for improving the design of future multi–redox–driven hybrid catalysts.

Understanding electrochemical interfaces through comparing experimental and computational charge density-potential curves.

Electrode-electrolyte interfaces play a decisive role in electrochemical charge accumulation and transfer processes. Theoretical modelling of these interfaces is critical to decipher the microscopic details of such phenomena. Different force field-based molecular dynamics protocols are compared here in a view to connect calculated and experimental charge density-potential relationships. Platinum-aqueous electrolyte interfaces are taken as a model. The potential of using experimental charge density-potential curves to transform cell voltage into electrode potential in force-field molecular dynamics simulations, and the need for that purpose of developing simulation protocols that can accurately calculate the double-layer capacitance, are discussed.

Evaluation of dynamics of charge accumulation and dissipation processes in Ge15Se85 thin film under electron beam irradiation by mapping surface potential distribution

The interaction of Ge15Se85 amorphous chalcogenide films with an electron beam has been studied. Three ranges of electron irradiation doses, in which a surface relief of various shapes is formed, are found. The presence and persistence of the surface potential for a long time after film irradiation have been established using the Kelvin probe force microscopy (KPFM). It is shown that the formation of surface relief is result of the charge accumulation in the interaction region. Based on the mapping of surface potential distribution in irradiated regions using KPFM we propose models of electric field distribution in the irradiated spots and suggest mechanism of electron-induced mass transfer. It has been suggested that the formation of a high surface relief structures is due to the electron-induced plastic effect. It is shown that the appearance of asymptotically sharp Taylor cones in chalcogenide films is due to charge collapse in the interaction region when the volume charge density and internal electric field strength exceed their critical values.

The Synergetic Ionic and Electronic Features of MAPbI3 Perovskite Films Revealed by Electrochemical Impedance Spectroscopy

AbstractPerovskites have emerged as a forerunner of electronics research due to their vast potential for optoelectronic applications. The numerous combinations of constituent ions and the potential for doping of perovskites lead to a high demand to track the underlying electronic properties. Solution‐based electrochemistry is particularly promising for detailed and facile assessment of perovskites. Here, electrochemical impedance spectroscopy (EIS) of methylammonium lead iodide (MAPbI3) thin films is performed and model them with an equivalent circuit that accounts for solvent, ionic, and thin film effects. A dielectric constant consistent with prior AC studies and a diffusion constant harmonious with cation motion in MAPbI3 are extracted. An electrical double layer thickness in the perovskite film of 54 nm is obtained, consistent with lithium doping in perovskite films. Comparing the EIS and equivalent circuit model of perovskite films to control ITO‐only data enabled the assignment of the ions at each interface. This comparison implied a double layer of primarily lithium ions inside the perovskite film at the solution interface with significant recombination of ions on the solution side of the interface. This demonstrates EIS as a powerful tool for studying the fundamental charge accumulation and transport processes in perovskite thin films.

Enhanced electrochemical activity of PVA assisted CuFe2O4 nanoparticles as a potential electrode for the fabrication of high energy density hybrid supercapacitor

Magnetic nanomaterials with unique physicochemical properties create a new era by providing enhanced electrochemical activity in the field of supercapacitors. In this work, the polyvinyl alcohol assisted copper ferrite (CFO-PVA) nanoparticles have been synthesized simple co-precipitation technique. The supercapacitor electrode materials have been fabricated by CFO-PVA electrode, delivering a high specific capacity of 169 C/g at 10 mV/s. based on the Trasatti method, the charge accumulation process has been identified and the total, outer, and inner capacities of CFO-PVA are 595.23, 8, and 587.23 C/g correspondingly and their contributions of capacitive and diffusion are 98% and 2% respectively. In addition, the CFO-PVA//AC hybrid supercapacitor device (HSC) has been prepared and their maximum specific capacitance is to be 60 C/g at the current density of 1 A/g together with their high energy density of about 18.75 Wh/kg and their respective high power density of 3012 W/kg.

Electronic effects of redox-active ligands on ruthenium-catalyzed water oxidation

The process of water oxidation presents a significant challenge in the development of artificial photosynthetic systems. This complexity arises from the necessity of charge accumulation, involving four electrons and four protons, and O–O bond formation. The strategy of using redox-active ligands in conjunction with metals is recognized as an effective approach for managing this charge accumulation process, attracting considerable attention. However, the detailed mechanisms by which the electronic effect of the redox-active ligands affect the reactivity of the catalytic centers remain ambiguous. In this study, the electronic effect of a series of mononuclear Ru complexes furnished with redox-active ligands ([(LRN5–)RuIII-OH]+, R = OMe, 3a; Me, 3b; H, 3c; F, 3d; CF3, 3e) was examined on water oxidation. A correlation was observed between redox potentials and substituent constants (σpara), indicating that different successive redox pairs are influenced by electron effects of varying intensities. Particularly, the ligand-centered oxidation (E {[(LN5–)+•RuIV=O]2+/[(LN5–)RuIV=O]+}) shows a greater dependence than the metal-centered PCET oxidations, E(RuIII-OH/RuII-OH2) and E(RuIV=O/RuIII-OH). The critical intermediate, [(LN5–)+•RuIV=O]2+, formed through ligand-centered oxidation, triggers O–O bond formation via its reaction with water. The rate constants of this crucial step can be effectively modulated by the substituents of the ligand. This study provides intricate insights into the role of the redox-active ligand in regulating the water oxidation process and further substantiates the effectiveness of the synergistic interaction of redox ligands and metals in controlling the multi-electron catalytic process.

A Novel Pump–Pump–Probe Resonance Raman Approach Featuring Light-Induced Charge Accumulation on a Model Photosystem

Light-induced charge accumulation is at the heart of biomimetic systems aiming at solar fuel production in the realm of artificial photosynthesis. Understanding the mechanisms upon which these processes operate is a necessary condition to drive down the rational catalyst design road. We have built a nanosecond pump–pump–probe resonance Raman setup to witness the sequential charge accumulation process while probing vibrational features of different charge-separated states. By employing a reversible model system featuring methyl viologen (MV) as a dual electron acceptor, we have been able to watch the photosensitized production of its neutral form, MV0, resulting from two sequential electron transfer reactions. We have found that, upon double excitation, a fingerprint vibrational mode corresponding to the doubly reduced species appears at 992 cm–1 and peaks at 30 μs after the second excitation. This has been further confirmed by simulated resonance Raman spectra which fully support our experimental findings in this unprecedented buildup of charge seen by a resonance Raman probe.

The effect of orthophosphoric acid on energy-intensive parameters of porous carbon electrode materials.

The effect of orthophosphoric acid concentration as an activating agent on the porous structure of carbon materials derived from apricot pits and energy-intensive parameters of electrochemical capacitors formed on their basis is studied. It is found that changing the ratio of the mass of the activating agent to the mass of the raw material in acid-activated porous carbon materials (PCMs), one can control the pore size distribution in the range of 0.5-20 nm and specific surface area in the range of 775-1830 m2/g. The use of cyclic voltammetry, impedance spectroscopy and chronopotentiometry made it possible to set the capacitive nature of charge accumulation processes in acid-activated PCMs, as well as to determine the contribution of a certain size of pores to the specific capacitance of PCM/electrolyte system.

Моделирование поверхностно-объемного заряжения диэлектрика электронами с энергией от 6 до 30 keV

The physico-mathematical model applied to ground tests for geomagnetic plasma exposure based on the combined consideration of surface and bulk processes of transport and charge accumulation for calculating the kinetics of charging high-resistance dielectrics irradiated by medium-energy monoenergetic electrons (from 6 to 30 keV) is proposed. The model takes into account the contribution to the charging of the dielectric by the trains of longitudinal optical phonons generated by each thermalizing primary electron with energy below the band gap of the dielectric, which supplements the induced conduction current due to the generation of electron-hole pairs. As a result, the current induced by trains of longitudinal optical phonons of the tunnel conductivity through free electron traps is introdused, as well as the current induced in the conduction band due to multiphonon ionization the electron traps by trains of longutudinal optical phonons in the region of existence of electric field. Using the example of the α-Al2O3 (sapphire) dielectric, the results of computer simulation of the internal currents distributions, charges, and electric field in the dielectric with the open surface irradiated by monoenergetic electrons with energies from 6 to 30 keV are presented according with the achievement the quasi-equilibrium in the irradiated part of the dielectric and with switching of the energy of primary electrons during the irradiation process.

Study of static charge accumulation in HDPE gas pipelines

The accumulation of static charge in polyethylene pipes of gas network systems is a familiar process, which is paid attention to mainly to prevent accidents on pipelines. incidents related to static electricity can occur both during assembly works (coil tapping) and during the operation of gas pipelines (gas venting, etc.). Despite the fact that repeated attempts to study this process have been made by major operating organizations, today we can state that these regularities have not been studied in full. In this work we have made an attempt to describe theoretically the process of static charge accumulation on a pipe body, as well as to evaluate experimentally the adequacy of the proposed models.

Mechanistic Understanding of Polarization‐Type Potential‐Induced Degradation in Crystalline‐Silicon Photovoltaic Cell Modules

Potential‐induced degradation (PID) has been identified as a central reliability issue of photovoltaic (PV) cell modules. Several types of PID depend on the cell structure. Among those types, polarization‐type PID, which is characterized by reductions in short‐circuit current density (JSC) and open‐circuit voltage (VOC), is the fastest PID mode. Additionally, polarization‐type PID occurs readily at room temperature or at markedly low magnitudes of electric potential difference. Therefore, polarization‐type PID is a severe difficulty affecting silicon PV modules. Recently, degradation behavior, preventive measures, and mechanism have been investigated. As described herein, mechanistic aspects of polarization‐type PID are specifically examined and details of a recently proposed model involving a charge accumulation process at K centers in SiNx dielectric layers: the K‐center model are discussed. The K‐center model consistently explains previously reported results of experimentation, which indicates the validity of this model. Discussions presented herein are expected to improve the mechanistic understanding of polarization‐type PID in the PV community and to stimulate further discussions and verifications of the model.

Ionic conductivity of the Ag8GeSe6 compound

The temperature dependences of the conductivity and permittivity of the Ag8GeSe6 compound have been studied in direct and alternating electric fields. This phenomenon is associated with the process of charge accumulation at the boundary of the sample with ionic conductivity and the blocking electrode, and the formation of a double electric layer. The observed dielectric relaxation is associated with the transition of the crystal to the superionic state. It has been established that hopping conduction with a variable hopping length over localized states near the Fermi level takes place in an Ag8GeSe6 crystal.

The Effective Capacitance of a Constant Phase Element with Resistors in Series

The power of energy storage devices is characterized by capacitance and the internal resistance. The capacitance is measured on an assumption that the charges are stored at the electrode interface and the electric double layer behaves like an ideal capacitor. However, in most cases, the electric double layer is not ideal so a constant phase element (CPE) is used instead of a capacitor to describe the practical observations. Nevertheless, another problem with the use of the CPE is that CPE does not give capacitance directly. Fortunately, a few methods were suggested to evaluate the effective capacitance in the literature. However, those methods may not be suitable for supercapacitors which are modeled as an equivalent circuit of a CPE and resistor connected in series because the time constant of the equivalent circuit is not clearly studied. In this report, in order to study the time constant of the CPE and find its equivalent capacitor, AC and DC methods are utilized in a complementary manner. As a result, the time constants in the AC and DC domains are compared with digital simulation and a proper equation is presented to calculate the effective capacitance of a supercapacitor, which is extended to an electrochemical system where faradaic and ohmic processes are accompanied by imperfect charge accumulation process.

Charging and Discharging Current Characteristics of Polypropylene Film under Varied Electric Fields

Charging and discharging current behavior under high DC electric field in polypropylene (PP) film is closely related to the charge transport and accumulation process, which has an important effect on the electrical insulating properties of PP. In this paper, the dependence of the charging and discharging current of polypropylene films on time and electric field has been comprehensively studied. The results showed that the transient and steady current values of the charging and discharging process increase with the increase of electric field. Dependence of the charging current on the electric field conformed well to the space charge limited current (SCLC) theory with a transition electric field of 270 kV/mm, at which the charge transport changed from ohmic conduction to SCLC conduction. The carrier mobility derived from the discharging current became significantly smaller with increase of the charging electric field. The charge accumulation after discharging was derived from the integration of the difference of the charging and discharging current and it showed an increase with the electric field and increased sharply above a certain threshold electric field (the same as the transition electric field in SCLC theory). It was proved that the conduction current and charge accumulation evolution and dependence on the electric field were mainly determined by the balance between the electrode charge injection process and the bulk conduction process.

Temporal Correlation Detection Based on 3D NAND Flash In-Memory Computing

The detection of temporal correlations among event-driven data streams is widely demanded in data-intensive applications such as edge computing. In this work, temporal correlation detection is enabled by the combination of 3D NAND flash and in-memory computing. Different from mathematical scheme by covariance matrix calculation, here the detection is implemented by exploiting the physical process of charge tunneling and accumulation. Thus the intrinsic charge-trapping dynamics in 3D NAND flash can be leveraged to perform in-memory computing. The computing results are stored and imprinted in the threshold voltages of the 3D NAND device array, enabling co-existence of computation and storage in the same devices. On this basis, the validation of temporal correlation detection further paves the way for 3D NAND application in high-level non-von Neumann computing.

Investigation of Charge Accumulation and Decay Processes in Epoxy-Based Composites Using Quantum Chemical Calculations Under the Effect of Electric Field

This work investigates the influence of aluminum nitride (AlN) fillers on the charge dynamics of epoxy resin (EP) and its hybrid composites through space charge measurements and quantum chemical calculations (QCCs). QCCs analyze the energy-level orbitals and trap parameters of the molecules under the electric field. The pure EP exhibits a homo-charge accumulation, whereas fewer charges are accumulated in the EP hybrid composites. The AlN filler addition significantly suppresses the space charge accumulation during polarization and facilitates the charge dissipation during the depolarization due to the lower trap density than the pure EP. It is found that the orbital energy level of the combined reaction of all monomers together is not a simple superposition of individual orbital energy levels of different monomers. The increased charge injection barrier height suppresses space charge injection and accumulation. The electric field significantly influences the hole traps more than the electron traps. The positive charges with low mobility are easily trapped inside hole traps compared with the negative charges with high mobility inside the electron traps. This results in positive charge accumulation during the polarization and slow decay during the depolarization. The increase of the electrostatic potential is more uniform in hybrid composites than in the pure EP, and no visible electron migration is observed. It indicates that hybrid composites remain stable under electric fields. Moreover, it is not easy for the hole to transport due to the deep trap after the charge injection, leading to limited visible space charge accumulation near the anode.