Charge Flow Research Articles

Reversal of nanomagnets by propagating magnons in ferrimagnetic yttrium iron garnet enabling nonvolatile magnon memory

Despite the unprecedented downscaling of CMOS integrated circuits, memory-intensive machine learning and artificial intelligence applications are limited by data conversion between memory and processor. There is a challenging quest for novel approaches to overcome this so-called von Neumann bottleneck. Magnons are the quanta of spin waves. Their angular momentum enables power-efficient computation without charge flow. The conversion problem would be solved if spin wave amplitudes could be stored directly in a magnetic memory. Here, we report the reversal of ferromagnetic nanostripes by spin waves which propagate in an underlying spin-wave bus. Thereby, the charge-free angular momentum flow is stored after transmission over a macroscopic distance. We show that the spin waves can reverse large arrays of ferromagnetic stripes at a strikingly small power level. Combined with the already existing wave logic, our discovery is path-breaking for the new era of magnonics-based in-memory computation and beyond von Neumann computer architectures.

Electrochemical Modelling of Na-MCl2 Battery Cells Based on an Expanded Approximation Method

Battery models are mathematical systems that aim to simulate real battery cell sufficiently accurately. Finding a comprise between complexity, computational effort and accuracy is thereby key. In particular, modelling sodium–nickel–chloride/iron-chloride cells (Na-NiCl2/FeCl2), as a promising alternative for stationary energy storage, bears some challenges. The literature shows a few interesting approaches, but in most of them the second active material (NiCl2 or FeCl2) or the entire discharging/charging cycle is not considered. In this work, an electrochemical and thermal model of Na-NiCl2/FeCl2 battery cells is presented. Based on an equivalent circuit approach combined with electrochemical calculations, the hybrid model provides information on the performance of the cell for charging and discharging with a constant current. By dividing the cathode space into segments, internal material and charge flows are predicted, allowing important insights into the internal cell processes. Besides a low calculation effort, the model also allows a flexible adaption of cathode composition and cell design, which makes it a promising tool for the development of single battery cells as well as battery modules and battery systems.

Prediction of Traffic Flow considering Electric Vehicle Market Share and Random Charging

This paper mainly studies the multiclass stochastic user equilibrium problem considering the market share of battery electric vehicles (BEVs) and random charging behavior (RCB) in a mixed transport network containing electric vehicles and gasoline vehicles (GVs). In order to analyze the random charging and path choice behaviors of BEV users and extract the differences in travel behaviors between BEV and GV users, an improved logit-based model, multilabel algorithm, and queuing theory are applied. The influencing factors of charging possibility mainly include the initial state of charge (SOC), the SOC at the beginning of charging, and the psychologically acceptable safe SOC threshold arriving at the destination. Diversity choices of user paths and charging locations will result in changes in queuing traffic and differences in queuing time. Conversely, different stations have different queuing dwell times, which will also affect the routing and charging locations for BEVs with RCB. The path-based method of successive averages (MSA) is adopted to solve the model. Through the simulation of the test network Sioux Falls, the equilibrium traffic flow and possible charging flow under different market shares and initial SOC are predicted, and the properties of the model and the feasibility of the algorithm are verified.

Thermal energy storage characteristics of finned tubes with different gradients of fin heights

Adding fins is considered to be a promising method to enhance heat transfer. As for the vertical latent thermal storage tube, it can be observed that the phase change materials in the upper part have much shorter charging time than in the lower part. To further enhance the heat transfer to boost the overall energy storage efficiency and reduce the apparent inhomogeneity of melting characteristics, fins with gradient height are packed. In this study, vertical shell-and-tube thermal energy storage tubes with fins of positive and negative gradient height are analyzed. After using experiments to verify the established numerical model, the phenomenological thermal characteristics are revealed and then additional analysis is used to investigate the thermal characteristics of the charging process, including melting, temperature distributions, and flow features. Results show that the negative gradient fins perform better than the positive gradient fins compared to the uniform ones. Furthermore, the complete melting time is reduced by 32.47% with a measured gradient of −0.8. A 42.11% enhancement in the time-integral average proportion of phase change materials (PCMs) in medium-temperature and a 78.74% suppression in the ratio of overheated PCMs at the final moment are achieved by the negative finned tube of −0.8 compared to a case with uniform fins. A tube with a higher bottom fin has a higher transient maximum velocity of the liquid phase transition material during melting, which also has a time-integral Grashof number (Gr) improvement of 31.46% compared to a uniform fin. The average energy storage is improved by using the negative gradient height fins of −0.8, as much as 1.34 times that of uniform height fins.

A Method for Evaluating and Optimizing Electric Bus Routes’ Efficiency that Uses Multi-perspective Charging and Passenger Flow Management--With Case Analysis in Hangzhou, China

This paper introduces a method and three indexes that could help evaluate the efficiency of city Electric Bus routes from different aspects, including the level of effective carrying capacity and overall operational cost. Most Electric Bus routes may see difficulty managing different vehicles’ charging and dispatching patterns and generate a large amount of wasted energy and human resources. Based on the case route in Hangzhou, China, and simulation conducted through calculation, showing this guidance and the indexes could enable people to spot the problem in operation and provide guidance for altering the charging-dispatching schedule to reduce approximately 20% of the operational inefficiency.

Influence of Geometry on Quasi-Ballistic Behavior in Silicon Nanowire Geometric Diodes

Diodes are a basic component of electrical circuits to control the flow of charge, and geometric diodes (GDs) are a special class that can operate using ballistic or quasi-ballistic transport in conjunction with geometric asymmetry to direct charge carriers preferentially in one direction, enabling an electron ratcheting effect. Nanomaterials present a unique platform for the development of GDs, and silicon nanowire (NW)-based GDs─cylindrically symmetric but translationally asymmetric three-dimensional nanostructures─have recently been demonstrated functioning at room temperature. These devices can theoretically achieve a near zero-bias turn-on voltage and rectify up to THz frequencies. Here, we synthesize silicon NW GDs and fabricate single-NW devices from which significant changes in diode performance are observed from relatively minor changes in geometry. To elucidate the interplay between geometry and ballistic behavior, we develop a Monte Carlo simulation that describes the quasi-ballistic behavior of electrons within a three-dimensional NW GD. We examine the effects of doping level, temperature, and geometry on charge carrier transport, revealing the relationships between charge carrier mean free path (MFP), specular reflection at surfaces, and geometry on GD performance. As expected, geometry strongly influences performance by directing or blocking charge carrier passage through the nanostructure. Interestingly, we find that the blocking effect is at least as important as the directing effect. Moreover, within certain geometric limits, the diode behavior is less sensitive to the MFP than might be initially expected because of the short relevant length scales and importance of the blocking effect. The results provide guidelines for the future design of NW GDs and enable the prediction and interpretation of trends in experimental results. An improved understanding of quasi-ballistic transport is crucial to guiding future experiments toward realizing THz rectification for applications in high-speed data transfer and long-wavelength energy harvesting.

Dynamics of recombination in viscous electron–hole plasma in a mesoscopic GaAs channel

The recombination dynamics are studied in viscous electron–hole plasma, consisting of electrons and photo-generated heavy and light holes, formed in the high-mobility mesoscopic GaAs channel. It is shown that an increase in the pump power reduces the concentration and mobility of background electrons, which, in turn, slows down their recombination with photogenerated holes. At a critical pump power, the recombination time begins to decrease, which is a consequence of the transition of a viscous electron–hole plasma from the hydrodynamic regime to the Drude diffusive regime. The observed transition occurs when the scattering of electrons with disorder begins to dominate over electron–electron scattering, which leads to the transformation of an inhomogeneous Poiseuille charge flow into a homogeneous diffusion flow. As a result, an optical analogue of the Gurzhi effect has been found.

In situ fabrication Ti3C2Fx MXene/CdIn2S4 Schottky junction for photocatalytic oxidation of HMF to DFF under visible light

It is highly demanded to steer the charge flow in semiconductors for efficient photocatalytic selective value-added conversion. In this study, we designed an interfacial contact Ti3C2 MXene/CdIn2S4 Schottky heterostructure which could greatly enhance the photogenerated charge separation of CdIn2S4. The study found that MXene/CdIn2S4 Schottky junction and ultra-thin nanostructures greatly promote the efficiency of photogenerated carriers separation and interface transfer. Compared with pure CIS, this heterostructure showed more excellent and stable HMF value-added conversion performance under natural conditions (DFF yield increased by 2.3 times). This work provides a new idea for MNs-based Schottky junction construction and a promising method for the photocatalytic value-added conversion of biomass under natural conditions.

Impact of Tourist Areas on the Electrical Grid: A Case Study of the Southern Dominican Republic

The growing integration of tourist areas and complexes increases the demand for electrical power systems. This increased demand may represent a vulnerability to voltage and frequency stability in electrical grids, where these parameters are essential for an optimal and continuous supply of electrical energy. The Dominican Republic has begun a tourist expansion process in areas that were previously not commercially exploited. Based on the factors mentioned above, this article’s objective was to analyze the impact caused by the increase in electricity demand due to the tourism sector, using the Enriquillo Region of the Dominican Republic as a case study. The impacts of this expansion on the voltage profiles and the system’s frequency were determined. The methodology consisted of obtaining information on the mathematical model of the system to evaluate the expansion plan for the study period and the projection of the demand of the grid. The complete system was modeled with this information, including expansion and possible renewable generators. Finally, the flow of charges was measured, and dynamic analysis was carried out. The quasi-dynamic and RMS/EMT simulations were carried out in the DIgSILENT software for this investigation. The results showed that the electrical system benefits stability and national standards. This is because the transmission lines reduced their loading by approximately 2.99% in 2032. As the years of study passed and the system load increased, the voltage in the bars of the 138 kV systems and generators did not exceed the range of ±5% established in the technical regulations of the Dominican electricity market.

Mechanistic insights into efficient photocatalytic H2O2 production of 2D/2D g-C3N4/In2S3 photocatalyst by tracking charge flow direction

Understanding the charge flow direction within semiconductor heterojunction is of crucial importance for designing and constructing next generation photocatalysts for fundamental perspective as well as efficient production of fuels such as hydrogen and hydrogen peroxide (H2O2). Here, two-dimensional (2D)/2D g-C3N4/In2S3 heterostructures are explored for photocatalytic H2O2 production in organic electron donor-free condition for the first time. The substantially augmented photocatalytic performance is unveiled by charge flow tracking realized through in situ reduction of Au ions by electron into Au and oxidation of Pb ions by hole into PbO2, revealing that photoinduced electrons of g-C3N4 move to In2S3 and holes remain in g-C3N4, prompting effective separation of charges. The experiments of radical trapping confirm that the photoexcited electrons accumulated on the conduction band of In2S3 in g-C3N4/In2S3 heterostructures generate H2O2 through a two-step one-electron reduction reaction of O2. This work not only identifies In2S3 as a new promising material for the photocatalytic H2O2 production but also provides a new approach for rational design of heterojunction photocatalyst via tracking charge flow direction to boost H2O2 production.

Effect of composition of geopolymer composites containing fly ash and waste glass powder on their durability and resistivity demonstrated in presence of a nanocarbon additive in a form of graphene

The objective of this study was to obtain a geopolymer composite with semi-conductive or conductive properties for self-control of abnormal symptoms caused by damages to its microstructure. For that purpose effects of different content of fly ash, waste glass powder, as well as two types of graphene and hydrophilic and hydrophobic nanosilica on electrical, physical and mechanical properties were tested. Measurements of resistivity showed the capacity for electrical charge flow in composites, which depended on their composition and products of the geopolymer hardening process. Based on results of the electrical charge flow intensity and observations of geopolymer composite microstructure by means of XRD and scanning microscopy, a possible course of the electrical conductivity mechanism in geopolymer materials was indicated. It was found that geopolymer composites containing fly ash, as well as addition of graphene and hydrophobic nanosilica, showed the most favourable electrical charge conductivity parameters and the highest strength gain.

Economic analysis of integrating photovoltaics and battery energy storage system in an office building

The concept of ‘Active Building’ refers to any building, such as factories, offices, homes, and other structures in the built environment, which are equipped to conserve, generate, store, and release energy in the UK. One such Active Building was built at Swansea University in the UK in 2018 and is currently used as a small office including well fare facilities. The objective of this study is to analyse the economic performance of an Active Building, incorporating building-integrated photovoltaics (BIPV) and lithium-ion (Li-ion) batteries with real building operational profiles and metered energy load profiles. The cost covers the capital cost of 22 kWp BIPV and 110 kWh Li-ion battery, and electricity cost from the electric grid with two types of time of use electricity tariffs - South Wales (SW) time of use tariff and Red, Amber, and Green (RAG) rates, and the potential carbon cost of electricity supplied from the Wales electric grid and generated from the Active Building. Four battery operational strategies are designed, and battery status of charge and electricity flow are monitored. The analysis is undertaken on the BIPV units with or without Li-ion batteries under various scenarios. The results show that the investment of BIPV units without Li-ion batteries can make a profit within the lifetime of BIPV in the current electricity market. However, the current Li-ion battery storage does not compensate for its capital cost from the reduced economic value obtained from the BIPV system when the electricity is curtailed. Even though the current economic analysis of the Active Building installing BIPV and battery is not convincing at the current capital price, this combination can enable the Active Building to be independent of the electric grid and to balance electricity demand and generation itself. The analysis will demonstrate the market conditions required to make these operational benefits cost-effective.

Ultrafast magnetization and energy flow in the laser-induced dynamics of transition metal compounds

An electronic theory of the laser-induced ultrafast magnetization dynamics in transition-metal alloys is presented. A many-body model Hamiltonian is considered that incorporates the fundamental electronic hopping, local Coulomb interaction, and spin-orbit coupling (SOC) on the same footing. Exact time propagations are performed on a tetrahedral cluster, from which the time dependencies of the local spin moments, orbital occupations, and single-particle energies of homogeneous systems and binary alloys are obtained. The consequences of inhomogeneities in the laser absorption and in the SOC strengths are investigated giving emphasis to the nature of spin-density transfers between the alloy components. A local perspective on the optically induced spin transfer is proposed in terms of which two main steps emerge: a dominantly local optical excitation followed by hopping-driven spin-density transfers among the different alloy components. The conjoint action of the spin-orbit interactions at the origin of local spin flips and spin-to-orbital angular-momentum transfer and the interatomic hoppings responsible for charge, spin, and energy flows between different sublattices is demonstrated. Transient and steady-state dynamical regimes are identified that result in delays in the onset of the local demagnetizations and in ultrafast redistributions of the spin. The central role of electron delocalization and electronic hopping in the spin-density redistribution and demagnetization of the different alloy components is demonstrated.

The disposition of bridge hydrogen bond in the homopolar-diborane and its derivatives

Compounds that comprehend less valence electrons are designated as electron deficient and atoms involved in such compounds occasionally form three-center-two-electron (3c-2e-) bonds to engross all of their available valence orbitals in bonding. Hence, in this study, calculations using M06-2X, MP2, and CCSD(T) method with the inclusion of def2-TZVP basis sets are exploited to reconnoiter the authentic bonding portrayal in diborane (DB) and its derivatives. Molecular electrostatic potential (MEP) analysis on the basis of vSmax and vSmin values indicates that there is a charge transfer between a π-hole that encompasses one monomer and the most negative region of another monomer that results in the formation of bridge bonds between two monomers. QTAIM investigation directed towards the charge depletion at bridging fragment in all the complexes and disclosed the polar covalent nature of bridge hydrogen bond. Additionally, ETS-NOCV examination suggests that charge flow from bridge to boron atom of all the complexes. Additionally, the bonding found to be more through orbital interactions compared to electrostatic interactions.

Origin of the anomalous Hall effect at the magnetic insulator/heavy metals interface

Ferrimagnetic insulators (FIMIs) are considered to be promising candidates in spin–orbit torque (SOT) devices due to their ability to propagate a spin current by magnons without Ohmic losses owing to the absence of electronic scattering. Moreover, any electrical current shunt is avoided in magnetic insulating materials. On the other hand, SOT-induced magnetization switching is generally measured through the anomalous Hall effect (AHE) in FIMI/heavy metal (HM) systems. However, the origin of AHE in FIMI/HM remains elusive since charges flow only in the HM. Here, we experimentally demonstrate that the AHE has the same origin as the spin Hall magnetoresistance (SMR). To this end, we have studied two bilayer heterostructures, Tm3Fe5O12(TmIG)/W and TmIG/Pt, where we ensure opposite spin Hall effect (SHE) signs for two heavy metals (W and Pt). The magnitudes of AHE and SMR are found to be larger for TmIG/W than TmIG/Pt. We have also evidenced the identical polarity of AHE hysteresis in both systems revealing a square dependency on the spin Hall angle whereas the current-induced magnetization switching polarity in TmIG/W is opposite to that of TmIG/Pt as expected for opposite spin Hall angle signs. Our results establish that the AHE and the spin-Hall magnetoresistance in TmIG insulating ferromagnets and heavy metal bilayers originate from the same mechanism.

Superbright quantum dots with inorganic caps

Inorganic semiconductor nanocrystals, or quantum dots, are widely used in commercial displays and imaging technology. They could be used in additional optoelectronic applications if their charge-transport properties could be improved without dimming their intense luminescence. A new study reports a way to do that by treating the crystals with metal salts to customize the quantum dots’ surface chemistry ( Nat. Commun. 2023, DOI: 10.1038/s41467-022-35702-7 ). Quantum dots are typically capped with long-chain hydrocarbon ligands to control crystal growth and stabilize the particles in colloidal suspensions. They also form electrically insulating barriers that impede charge flow between particles, a property needed for electronic applications. Replacing the organic ligands with inorganic ones can boost charge transport, but that approach can reduce luminescence by over 75%. Yuanyuan Wang of Nanjing University, Dmitri V. Talapin of the University of Chicago, and coworkers treated organically capped quantum dots with salts of cadmium, zinc, and other

Review of bubble dynamics on charged liquid–gas flow

When a fluid is subject to an electric field, it usually processes unique features compared to the conventional fluid that arises from coupling between charged particles and fluid interface. Based on this commonality, we defined the concept of “charged multiphase flow” and constructed a generalized charged multiphase flow system using the “Tai Chi Diagram” to analyze the properties and features of different study objects, with an emphasis on the bubble dynamics on the charged liquid–gas flow object, covering the processes of bubble generation, motion, and interaction, as well as the important dynamic behaviors, involved such as bubble deformation, coalescence, and breakup. Furthermore, in light of the special plasma–liquid interface phenomenon formed by the ionization of the gas/vapor phase in the liquid phase in strong electric fields, the traditional gas–liquid–solid three-phase flow system is expanded into a broader range of multiphase flow systems involving plasma, which enriches the theoretical and frontier scientific problems of the multiphase flow. In addition, technical innovations, remaining work, and future trends in the development of the charged liquid–gas flow, and their potential applications are discussed.

Interface-Dependent Selectivity in Plasmon-Driven Chemical Reactions

Plasmonic nanoparticles can drive chemical reactions powered by sunlight. These processes involve the excitation of surface plasmon resonances (SPR) and the subsequent charge transfer to adsorbed molecular orbitals. Nonetheless, controlling the flow of energy and charge from SPR to adsorbed molecules is still difficult to predict or tune. Here, we show the crucial role of halide ions in modifying the energy landscape of a plasmon-driven chemical reaction by carefully engineering the nanoparticle-molecule interface. By doing so, the selectivity of plasmon-driven chemical reactions can be controlled, either enhancing or inhibiting the metal-molecule charge and energy transfer or by regulating the vibrational pumping rate. These results provide an elegant method for controlling the energy flow from plasmonic nanoparticles to adsorbed molecules, in situ, and selectively targeting chemical bonds by changing the chemical nature of the metal-molecule interface.

Growth dominated crystallization of GeTe mushroom cells during partial SET operation

Phase change memory devices are a leading candidate for non-volatile memory arrays, as artificial synapses in neuromorphic circuits, and for in-memory computing. These applications are hampered by a large cycle-to-cycle variation of resistance that is likely associated with the crystallization mechanism of phase change materials. This work presents a direct observation by transmission electron microscopy of the crystallization process during the SET operation of the GeTe 100 nm mushroom cell. The process proceeded purely by growth from the periphery of the amorphous dome without nucleation. It is invariably associated with partial melting of the GeTe layer. The growth-dominated SET operation can completely crystallize the GeTe functional layer only by a gradual sweep down of the voltage across the device. The experimental results were correlated with a finite element model of heat and charge flow and the crystallization dynamics.

Regulating Nonlinear Ion Transport through a Solid-State Pore by Partial Surface Coatings

Using functional nanofluidic devices to manipulate ion transport allows us to explore the nanoscale development of blue energy harvesters and iontronic building blocks. Herein, we report on a method to alter the nonlinear ionic current through a pore by partial dielectric coatings. A variety of dielectric materials are examined on both the inner and outer surfaces of the channel with four different patterns of coated or uncoated surfaces. Through controlling the specific part of the surface charge, the pore can behave like a resistor, diode, and bipolar junction transistor. We use numerical simulations to find out the reason for the asymmetric ion transport in the pore and illustrate the relationship between specifically charged surfaces and electroosmotic flow. These findings help understand the role of the corresponding surface composition in ion transport, which provides a direct approach to modify the electroosmotic-flow-driven ionic current rectification in the channel-based device via dielectric coatings.