Charged Walls Research Articles

Exploring the Reconfigurable Memory Effect in Electroforming-Free YMnO3-Based Resistive Switches: Towards a Tunable Frequency Response.

Memristors, since their inception, have demonstrated remarkable characteristics, notably the exceptional reconfigurability of their memory. This study delves into electroforming-free YMnO3 (YMO)-based resistive switches, emphasizing the reconfigurable memory effect in multiferroic YMO thin films with metallically conducting electrodes and their pivotal role in achieving adaptable frequency responses in impedance circuits consisting of reconfigurable YMO-based resistive switches and no reconfigurable passive elements, e.g., inductors and capacitors. The multiferroic YMO possesses a network of charged domain walls which can be reconfigured by a time-dependent voltage applied between the metallically conducting electrodes. Through experimental demonstrations, this study scrutinizes the impedance response not only for individual switch devices but also for impedance circuitry based on YMO resistive switches in both low- and high-resistance states, interfacing with capacitors and inductors in parallel and series configurations. Scrutinized Nyquist plots visually capture the intricate dynamics of impedance circuitry, revealing the potential of electroforming-free YMO resistive switches in finely tuning frequency responses within impedance circuits. This adaptability, rooted in the unique properties of YMO, signifies a paradigm shift heralding the advent of advanced and flexible electronic technologies.

Diffusiophoresis of a Charged Soft Sphere in a Charged Spherical Cavity

The quasi-steady diffusiophoresis of a soft particle composed of an uncharged hard sphere core and a uniformly charged porous surface layer in a concentric charged spherical cavity full of a symmetric electrolyte solution with a concentration gradient is analyzed. By using a regular perturbation method with small fixed charge densities of the soft particle and cavity wall, the linearized electrokinetic equations relevant to the fluid velocity field, electric potential profile, and ionic concentration distributions are solved. A closed-form formula for the diffusiophoretic (electrophoretic and chemiphoretic) velocity of the soft particle is obtained as a function of the ratios of the core-to-particle radii, particle-to-cavity radii, particle radius to the Debye screening length, and particle radius to the permeation length in the porous layer. In typical cases, the confining charged cavity wall significantly influences the diffusiophoresis of the soft particle. The fluid flow caused by the diffusioosmosis (electroosmosis and chemiosmosis) along the cavity wall can considerably change the diffusiophoretic velocity of the particle and even reverse its direction. In general, the diffusiophoretic velocity decreases with increasing core-to-particle radius ratios, particle-to-cavity radius ratios, and the ratio of the particle radius to the permeation length in the porous layer, but increases with increasing ratios of the particle radius to the Debye length.

Root nutrition of plants: relevance, needs, problem solving

The article theoretically analyzes the nutrient needs of plants and the balanced supply of macro- and microelements for their proper growth and development. The basis of the research methodology is the systematic approach of assessing the periodicity of foliar feeding of plants with complex preparations of various compositions. It has been established that with foliar fertilization there is a part of nutrients after they enter the plant leaf. Smaller molecules or molecules with less positive charge are more easily transported in the vascular system, from where they move to other parts of the plant, including ammonium, potassium, and urea. On the other hand, larger molecules and ions with a large positive charge tend to stay fairly close to their point of entry because they stick to the negatively charged cell walls. They hold immobile nutrients quite tightly, including calcium, iron, manganese, zinc, and copper. The importance of the combination of biotechnological and ecological aspects in the development and application of complex compounds for foliar fertilization is indicated. The use of compounds based on EDTA is potentially dangerous for agricultural products and the environment. In the long term, this leads to increased pollution of agricultural land, soil degradation, reduced yield, and deterioration of product quality. When applying complex foliar fertilizers, elements with a strong positive charge, such as calcium, do not move very actively in the plant. Accordingly, negatively charged elements, such as phosphorus, slowly enter the leaves of plants. Both elements are relatively stationary after entry. Additional studies have shown that different plant species differ significantly in their ability to absorb nutrients through their leaves. Differences in cuticle thickness, number of pores, and resistance, as well as genetic and environmental factors, all affect a species’ ability to assimilate nutrients applied to leaves.

Effects of electric double layer on nanoscale boiling: Molecular dynamics approach

Electric double layers (EDL) are formed in aqueous solution of electrolytes near electrically charged wall. Such EDLs play a crucial role in many interfacial phenomena, among which a nanoscale boiling process was studied with molecular dynamics simulations. Evaporation and boiling were investigated with aqueous solution of sodium chloride (NaCl), a typical inorganic electrolyte, in contact with an artificially charged platinum substrate. The heating area temperature of the substrate was controlled in a range from 500 to 800K. The results indicate that the surface charge and the formed EDL suppress the bubble nucleation due to strengthened interaction between liquid molecules and the substrate. It was also shown that water molecules in the EDL exhibit orientational ordering even at higher temperatures.

Unit‐Cell‐Thickness Electron Confinement by Geometrically Constrained Antipolar Ordering

AbstractAchieving precise electron or spin confinement is essential for the progress of oxide electronics and emerging quantum information processing. While 2D electron confinement is commonly achieved with bare surfaces, heteroepitaxial interfaces, and charged domain walls, its practical application poses challenges, notably by diverse confinement widths, limited material selection, and the lack of freedom of positioning to a desired location within a given material system. Here, with scrutinizing a novel defect structure, the study suggests a new strategy with compelling evidence to trigger electron confinement down to single unit‐cell‐thickness, through geometrically constrained antipolar ordering facilitated by superlattice‐like periodic planar faults in metallic SrFeO3. Employing atomic resolution electron microscopy and density functional theory, the results demonstrate that electrons are confined two‐dimensionally to screen the positive bound charges on head‐to‐head antipolar state boundary, meanwhile oxygen vacancies segregated in the planar faults compensate the negative bound charges on the tail‐to‐tail one, leading to the stabilization of the antipolar ordering. Additionally, distinguished from traditional methods, this approach offers a potential programing capability for achieving precise charge and spin control by regulating planar fault structure at atomic scale.

Modeling of nanochannels in synthetic membranes

The behavior of a diluted electrolyte in a system of joint microchannel and nanochannel with charged dielectric walls under the action of external potential difference and external pressure is investigated numerically. The surface charge on the nanochannel walls prevents the ions of corresponding polarity from passing through it. Consequently, the system in question acquires ion-selective properties and can, under certain assumptions, be viewed as a fragment of an ion-selective membrane, including one synthesized by creating nanopores in a dielectric material. Such systems are used in experiments to control the movement of charged particles through concentration polarization. The objective of the work is to investigate the influence of a single pore on electrolyte flow and the possibilities to control that flow by changing the geometric and physical properties of the pore. The investigation relies on the specially developed simplified models based on cross-section-averaged Nernst-Planck, Poisson and Stokes equations that are subsequently reduced to a single nonlinear differential equation. The simplified models allow identifying the impact of different physical mechanisms of electrolyte movement: pressure-based (generated by the external mechanical action) and electroosmotic (generated by the electric field). A finite-difference method with semi-implicit time integration is used for the numerical solution of equations. It has been found that the behavior of the system qualitatively matches the behavior of a cell based on a non-ideally-selective ion-exchange membrane. In particular, the model correctly predicts the underlimiting and limiting electric current regimes, as well as vortex formation near the nanochannel inlet due to concurrency between electrolyte movement mechanisms. The proposed models can be extended to describe a channel with arbitrary geometry and an electrolyte with arbitrary number of charged species.

Concomitant Light-Reversible Magnetic Response in Multiferroic Oxide Heterostructures for Multiphysics Applications.

The concept of multiphysics, where materials respond to diverse external stimuli, such as magnetic fields, electric fields, light irradiation, stress, heat, and chemical reactions, plays a fundamental role in the development of innovative devices. Nanomanufacturing, especially in low-dimensional systems, enhances the synergistic interactions taking place on the nanoscale. Light-matter interaction, rather than electric fields, holds great promise for achieving low-power, wireless control over magnetism, solving two major technological problems: the feasibility of electrical contacts at smaller scales and the undesired heating of the devices. Here, we shed light on the remarkable reversible modulation of magnetism using visible light in epitaxial Fe3O4/BaTiO3 heterostructure. This achievement is underpinned by the convergence of two distinct mechanisms. First, the magnetoelastic effect, triggered by ferroelectric domain switching, induces a proportional change in coercivity and remanence upon laser illumination. Second, light-matter interaction induces charged ferroelectric domain walls' electrostatic decompensations, acting intimately on the magnetization of the epitaxial Fe3O4 film by magnetoelectric coupling. Crucially, our experimental results vividly illustrate the capability to manipulate magnetic properties using visible light. This concomitant mechanism provides a promising avenue for low-intensity visible-light manipulation of magnetism, offering potential applications in multiferroic devices.

Spatial extension of the transient gain drop in a microchannel plate for a single-pulse irradiation

It is widely recognized that a microchannel plate gain drops temporarily after a particle initiates an electron avalanche and that a large amount of charge is extracted from the channel. Electron multiplication is expected to deplete the charges from the microchannel and produce depleted charges (wall charges), and this gain drop is known to persist until charges are replenished. In addition, it was reported that a gain drop occurs not only in the activated channels, where the electrons are multiplied, but also in the surrounding channels. A proposed mechanism for this phenomenon is suggested that the wall charges in the activated channels change the electric field in the surrounding channels, which affects the electron multiplications. In this study, the spatial extent of the gain drop of a chevron microchannel plate detector was evaluated by measuring gains as a function of distance from an activated channel. The experiment used two ultraviolet pulses with different beam sizes, which initially activated one channel and the six neighboring channels with carefully focused laser light, and then applied another light pulse to the surrounding 900 μm × 30 μm area. The gain of each channel was measured using a charge-coupled device camera, and the change in gain as a function of the output charge for the laser pulse was analyzed. A gain drop of 20% was observed at a channel located 110 μm far from the initial activated channel when the output charge was 4 pC. The obtained relationship between the radius of gain drop area and the output charge for the laser pulse was in good agreement with that predicted from the transverse electric field due to the wall charges by computational analysis.

Curvature conservation and conduction modulation for symmetric charged ferroelectric domain walls

Curvature conservation is a common feature for the physical properties with topological constraints, from the macroscopic cosmic string loops to the microscopic quantized vortex rings in the superfluid. Interestingly, ferroelectric domain-wall curvature is important to determine its conduction, which is the key parameter for designing domain-wall nanoelectronic devices. Here, we demonstrate the curvature conservation of the charged domain walls confined in ferroelectric topological structures with specific domain symmetry by combining piezoelectric force microscopy, conducting atomic force microscopy, and phase-field simulations. Significantly, the intrinsic conductivity of the charged domain walls exhibits an inverse functional relationship with the local domain-wall curvature in the ferroelectric BiFeO3 nano-islands, which can also be precisely and continuously modulated by applying an electric field. This work provides us with an insightful understanding of the conduction mechanism of charged domain walls confined in ferroelectric topological structures with a high degree of spatial symmetry, which paves the way for the application of charged domain walls as flexible conducting channels with continuously changing resistance states to be used for ferroelectric domain-wall memristors.

Interface engineering for facile switching of bulk-strong polarization in Si-compatible vertical superlattices

Ferroelectric thin films incorporating different compositional layers have emerged as a promising approach for enhancing properties and performance of electronic devices. In recent years, superlattices utilizing various interactions between their constituent layers have been used to reveal unusual properties, such as improper ferroelectricity, charged domain walls, and negative capacitance in conventional ferroelectrics. Herein, we report a symmetry scheme based on the interface engineering in which the inherent cell-doubling symmetry allowed atomic distortions (phonons) in any vertically aligned superlattice activate novel interface couplings among atomic distortions of different symmetries and fundamentally improve the ferroelectric properties. In a materialized case, the ionic size difference between Hf4+ and Ce4+ in the HfO2/CeO2 (HCO) ferroelectric/paraelectric superlattice leads to these couplings. These couplings mitigate the phase boundary between polar and non-polar phases, and facilitate polarization switching with a remarkably low coercive field (Ec\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${E}_{c}$$\\end{document}) while preserving the original magnitude of the bulk HfO2 polarization and its scale-free ferroelectric characteristics. We show that the cell-doubled distortions present in any vertical superlattice have unique implications for designing low-voltage ferroelectric switching while retaining bulk-strong charge storing capacities in Si-compatible memory candidates.

Phase-field theory study on the modulation mechanism of oxygen vacancy concentration on charged domain wall in ferroelectric thin films

This study analyzes the regulatory mechanism of oxygen vacancy concentration on tail-to-tail charged domain walls (T–T CDWs), along with the writing time, conduction current magnitude, and retention performance of through-type T–T CDWs. The research results show that the highest density and length of T–T CDWs are achieved when the oxygen vacancy concentration is 1 × 1020 cm−3. Moreover, the successful writing of through-type T–T CDWs is limited to a certain electric field range, which is controlled by oxygen vacancy concentration. An increase in the oxygen vacancy concentration leads to a decrease in the maximum and minimum threshold electric fields required for writing through-type charged domain walls. The writing time and conductivity of through-type T–T CDWs determine the information writing speed and signal strength of domain wall memories, and the oxygen vacancy concentration also plays a regulatory role in both aspects. When the oxygen vacancy concentration is 1 × 1020 cm−3, the through-type T–T CDW exhibits the fastest writing speed, requiring only 8 ns. The magnitude of the conduction current of through-type T–T CDWs is directly proportional to the oxygen vacancy concentration. The through-type T–T CDWs formed by the aggregation of oxygen vacancies exhibit excellent retention performance, making them highly promising for applications in ferroelectric domain wall memories. Our research demonstrates that oxygen vacancies have a significant regulatory effect on the morphology and current response of charged domain walls, opening up new avenues for the study of domain wall memories.

Reversible charge injection in artificially created charged domain wall region

The impact of electric field application in the charged domain wall (DW) region on the performance of DW devices remains elusive. Here, we present our observations of substantial charge injection occurring in an artificially created charged DW region. Rapid charge injection coincides with polarization switching, contributing to the transient current collected for the integration of polarization-voltage hysteresis loops. Subsequently, a gradual injection of charges persists under externally applied voltages, diffusing into the thin film from the DW region to screen the space defect dipoles and effectively suppressing the imprint field. The process of charge injection proves reversible and is notably more pronounced in aged ferroelectric thin films, as evidenced in planar BiFeO3 nanodevices where the charge injection amount is five orders of magnitude higher than charges generated from polarization switching. This work constitutes a significant contribution to understanding the intricate process of charge injection and its influence on charged DW.

Intermittent discharge in a complex stripe pattern in dielectric barrier discharge

The intermittent discharge that filament only discharges once in a cycle rather than once every half-cycle is observed in all the three substructures of the (bright spots)–(dark spots)-halo stripe pattern (BDHSP) in dielectric barrier discharge. The discharge characteristics are investigated by a high-speed video camera, an intensified charge-coupled device camera, and two photomultiplier tubes. It is found that the direction of the stripe choose to form in BDHSP is determined by the direction in which the surface discharge is stronger in the square pattern. The spatiotemporal dynamics results of BDHSP suggest that bright spot (B) discharges in this half-cycle, and the dark spot (D) and the halo (H) discharge in the next half-cycle of the applied voltage, which is intermittent discharge. Combined with the analysis in the electric field simulation, it can be concluded that the intermittent discharge is the result of the mutual influence between the directional selective surface discharge induced by bright spots and dark spots. Overall, the BDHSP is formed by the self-organization of the wall charge under the interaction between the plasma physical processes and the spatial distribution. The discovery of the intermittent discharge provides insight and enlightenment for the study of plasma physics.

Ion transport through short nanopores modulated by charged exterior surfaces.

Short nanopores find extensive applications, capitalizing on their high throughput and detection resolution. Ionic behaviors through long nanopores are mainly determined by charged inner-pore walls. When pore lengths decrease to sub-200nm, charged exterior surfaces provide considerable modulation to ion current. We find that the charge status of inner-pore walls affects the modulation of ion current from charged exterior surfaces. For 50-nm-long nanopores with neutral inner-pore walls, the charged exterior surfaces on the voltage (surfaceV) and ground (surfaceG) sides enhance and inhibit the ion transport by forming ion enrichment and depletion zones inside nanopores, respectively. For nanopores with both charged inner-pore and exterior surfaces, continuous electric double layers enhance the ion transport through nanopores significantly. The charged surfaceV results in higher ion current by simultaneously weakening the ion depletion at pore entrances and enhancing the intra-pore ion enrichment. The charged surfaceG expedites the exit of ions from nanopores, resulting in a decrease in ion enrichment at pore exits. Through adjustment in the width of charged-ring regions near pore boundaries, the effective charged width of the charged exterior is explored at ∼20nm. Our results may provide a theoretical guide for further optimizing the performance of nanopore-based applications, such as seawater desalination, biosensing, and osmotic energy conversion.

In-bulk polarization reversal in lithium tantalate with single charged domain wall

This paper presents the results of the first experimental observation of polarization reversal in the bulk of ferroelectric with a charged domain wall (CDW) under the action of an electric field on the example of a single crystal LiTaO3 plate. A CDW was obtained in the sample bulk at the locus of points with a sign change of the composition gradient which results from sample annealing in lithium rich atmosphere. Imaging of the domain structure in the bulk and its evolution on the surface made it possible to detect anomalous domain kinetics, which represents the growth of ledges on the CDW toward the polar surface. The main stages of the domain structure evolution on the polar surface, including the growth of isolated domains, as well as the formation and decay of the maze domain structure, were revealed. An analysis is made for the time dependence of the area fraction occupied by growing domains. We used a kinetic approach based on the analogy between the growth of domains and crystals to explain the obtained results.

Theory of cuprate pseudogap as antiferromagnetic order with charged domain walls

Theory of cuprate pseudogap as antiferromagnetic order with charged domain walls

Biotrapping Ureolytic Bacteria on Sand to Improve the Efficiency of Biocementation.

Microbially induced calcium carbonate precipitation (MICP) has emerged as a novel technology with the potential to produce building materials through lower-temperature processes. The formation of calcium carbonate bridges in MICP allows the biocementation of aggregate particles to produce biobricks. Current approaches require several pulses of microbes and mineralization media to increase the quantity of calcium carbonate minerals and improve the strength of the material, thus leading to a reduction in sustainability. One potential technique to improve the efficiency of strength development involves trapping the bacteria on the aggregate surfaces using silane coupling agents such as positively charged 3-aminopropyl-methyl-diethoxysilane (APMDES). This treatment traps bacteria on sand through electrostatic interactions that attract negatively charged walls of bacteria to positively charged amine groups. The APMDES treatment promoted an abundant and immediate association of bacteria with sand, increasing the spatial density of ureolytic microbes on sand and promoting efficient initial calcium carbonate precipitation. Though microbial viability was compromised by treatment, urea hydrolysis was minimally affected. Strength was gained much more rapidly for the APMDES-treated sand than for the untreated sand. Three injections of bacteria and biomineralization media using APMDES-treated sand led to the same strength gain as seven injections using untreated sand. The higher strength with APMDES treatment was not explained by increased calcium carbonate accrual in the structure and may be influenced by additional factors such as differences in the microstructure of calcium carbonate bridges between sand particles. Overall, incorporating pretreatment methods, such as amine silane coupling agents, opens a new avenue in biomineralization research by producing materials with an improved efficiency and sustainability.

Oxygen vacancies stabilized 180° charged domain walls in ferroelectric hafnium oxide

Ferroelectric domain walls (DWs) are spatial interfaces separating domains with distinct polarization orientations. Among these DWs, some can carry bound charges and display metallic-like conductivity. The feature is highly of interest for future nanoelectronics. However, the inherent instability of charged domain walls (CDWs) has posed a critical challenge for their experimental exploration. This Letter reports the head-to-head (HH) and tail-to-tail (TT) 180° CDWs within the context of ferroelectric hafnium oxide. We proposed that oxygen vacancy is a crucial factor stabilizing the periodic CDWs. Through meticulous first-principles calculations, we elaborated on the intricate properties of these CDWs, including their polarization profiles, and potential and charge distributions. Furthermore, we calculated the energy barrier for layer-by-layer propagation of a HH wall and carefully discussed the migration of a TT wall with oxygen vacancy. Our study can shed more light onto the characteristics of CDWs and their implications to hafnia-based ferroelectric devices.

Study of restricted diffusion of lithium salts in diglyme confined in mesoporous carbons as a model for cathodes in lithium-air batteries.

The Li+ ion mobility through the porous cathode is a critical aspect in the development of commercial Li-air batteries. The bulk transport properties of lithium salts in organic solvents are not reliable parameters for the design of this type of battery since confinement could significantly modify the transport properties, especially when pore diameters are below 10 nm. In this work, we studied the effect of the carbon mesostructure and surface charge on the diffusion of LiTf and LiTFSI salts dissolved in diglyme, typical electrolytes for lithium-air batteries. Interdiffusion coefficients of the salts were determined using a conductimetric method. NMR spectroscopy and relaxometry were used to explore the effect of the carbon structure and the surface charge density on the interaction between the electrolytes and the pore wall. We showed that carbon micro/mesoporous structure plays a critical role in the transport properties of the electrolyte, producing a decrease of up to 2-3 orders of magnitude in the salt interdiffusion coefficients when going from bulk solutions to pores below 4 nm in diameter. It was observed that for pores 25 nm in diameter, the reduction in the diffusion coefficient can be mainly ascribed to the porosity of the sample, giving tortuosity factors around 1. However, for smaller pore sizes (1-10 nm diameter) bigger tortuosity coefficients were observed and were related to strong ion-pore wall interactions. Moreover, it was noticed that the ratio between the diffusion coefficients of the two studied salts dissolved in diglyme, is different in bulk and under confinement, demonstrating that the interactions of the ions with the charged pore wall probably compete with the cation-anion interactions, affecting salt association under confinement.

Polyaniline nanofiber: an excellent anode material for microbial fuel cells.

Sluggish electron transfer from the bacterial metabolic system to the electrode is a critical issue in microbial fuel cell (MFC) research. However, a number of strategies have already been demonstrated for the improved performance of MFCs through the chemical or electrochemical manipulation of the anode. In this study, a new anode fabrication technique was introduced with polyaniline nanofibers (PANInf) to increase the surface area of the anode in a three-dimensional pattern. A large number of bacteria were anchored to the high surface area anode through the electrostatic interaction between positively charged anode surface and negatively charged bacteria cell wall. An improved conductive nature also plays an important role in accelerating the electron transfer process, yielding a current density of 0.87 mA cm-2, which is almost a 73% increase from that of the PANI anode (0.503 mA cm-2). The maximum power density with a PANInf-modified anode was 1091 ± 5% mW m-2, which is 40% higher than that of the PANI-modified anode (777 ± 5% mW m-2). Impedance spectroscopic study shows that PANInf modification reasonably reduces the charge transfer resistance, leading to faster electron transfer kinetics.