Local Electric Field Distribution Research Articles

All‐in‐One: Plasmonic Janus Heterostructures for Efficient Cooperative Photoredox Catalysis

Janus heterostructures consisting of multiple jointed components with distinct properties have gained growing interest in the photoredox catalytic field. Herein, we have developed a facile low‐temperature method to gain anisotropic one‐dimensional Au‐tipped CdS (Au‐CdS) nanorods (NRs), followed by assembling Ru molecular co‐catalyst (RuN5) onto the surface of the NRs. The CdS NRs decorated with plasmonic Au nanoparticles (NPs) and RuN5 complex harness the virtues of metal‐semiconductor and inorganic‐organic interface, giving directional charge transfer channels, spatially separated reaction sites, and enhanced local electric field distribution. As a result, the Au‐CdS‐RuN5 can act as an efficient dual‐function photocatalyst for simultaneous H2 evolution and valorization of biomass‐derived alcohols. Benefiting from the interfacial charge decoupling and selective chemical bond activation, the optimal all‐in‐one Au‐CdS‐RuN5 heterostructure shows greatly enhanced photoactivity and selectivity as compared to bare CdS NRs, along with a remarkable apparent quantum yield of 40.2% at 400 nm. The structural evolution and working mechanism of the heterostructures are systematically analyzed based on experimental and computational results.

All-in-One: Plasmonic Janus Heterostructures for Efficient Cooperative Photoredox Catalysis.

Janus heterostructures consisting of multiple jointed components with distinct properties have gained growing interest in the photoredox catalytic field. Herein, we have developed a facile low-temperature method to gain anisotropic one-dimensional Au-tipped CdS (Au-CdS) nanorods (NRs), followed by assembling Ru molecular co-catalyst (RuN5) onto the surface of the NRs. The CdS NRs decorated with plasmonic Au nanoparticles (NPs) and RuN5 complex harness the virtues of metal-semiconductor and inorganic-organic interface, giving directional charge transfer channels, spatially separated reaction sites, and enhanced local electric field distribution. As a result, the Au-CdS-RuN5 can act as an efficient dual-function photocatalyst for simultaneous H2 evolution and valorization of biomass-derived alcohols. Benefiting from the interfacial charge decoupling and selective chemical bond activation, the optimal all-in-one Au-CdS-RuN5 heterostructure shows greatly enhanced photoactivity and selectivity as compared to bare CdS NRs, along with a remarkable apparent quantum yield of 40.2% at 400 nm. The structural evolution and working mechanism of the heterostructures are systematically analyzed based on experimental and computational results.

Statistical field theory of polarizable polymer chains with nonlocal dipolar interactions.

The electromechanical response of polymeric soft matter to applied electric fields is of fundamental scientific interest as well as relevant to technologies for sensing and actuation. Several existing theoretical and numerical approaches for polarizable polymers subject to a combined applied electric field and stretch are based on discrete monomer models. In these models, accounting for the interactions between the induced dipoles on monomers is challenging due to the nonlocality of these interactions. On the other hand, the framework of statistical field theory provides a continuous description of polymer chains that potentially enables a tractable way to account for these interactions. However, prior formulations using this framework have been restricted to the case of weak anisotropy of the monomer polarizability. This paper formulates a general approach based in the framework of statistical field theory to account for the nonlocal nature of the dipolar interactions without any restrictions on the anisotropy or nonlinearity of the polarizability of the monomer. The approach is based on three key elements: (1) the statistical field theory framework, in which the discrete monomers are regularized to a continuous dipole distribution, (2) a replacement of the nonlocal dipole-dipole interactions by the local electrostatics partial differential equationwith the continuous dipole distribution as the forcing, and (3) the use of a completely general relation between the polarization and the local electric field. Rather than treat the dipole-dipole interactions directly, the continuous description in the field theory enables the computationally tractable nonlocal-to-local transformation. Further, it enables the use of a realistic statistical-mechanical ensemble wherein the average far-field applied electric field is prescribed, rather than prescribing the applied field at every point in the polymer domain. The model is applied, using the finite element method, to study the electromechanical response of a polymer chain in the ensemble with fixed far-field applied electric field and fixed chain stretch. The nonlocal dipolar interactions are found to increase, over the case where dipole-dipole interactions are neglected, the magnitudes of the polarization and electric field by orders of magnitude as well as significantly change their spatial distributions. Next, the effect of the relative orientation between the applied field and the chain on the local electric field and polarization is studied. The model predicts that the elastic response of the polymer chain is linear, consistent with the Gaussian approximation, and largely unchanged by the orientation of the applied electric field, though the polarization and local electric field distributions are significantly impacted.

Local electric field enhancement in the vicinity of aggregates of Ag, Au, Rb containing nanoparticles in oxide glasses

Local electric field (LEF) distribution near Ag, Au, AgAu NPs synthesized by UV laser or temperature treatments, and near simulated Rb, AgRb, AuRb NPs in oxide glasses, was studied considering aggregates of 10–15 particles - necessary condition for description of optical extinction spectra. For efficient analysis of LEF spatial distributions under different sizes, components, agglomerations of NPs in these aggregates, approach was proposed that enables to obtain dependence of averaged LEF enhancement upon the distance from the nearest particles in aggregate. This approach reproduced enhancement of Er3+ luminescence intensity in zinc-tellurite glass after formation of Ag NPs and showed that average LEF enhancement per hypothetical Rare Earth ion (REI) is largest for aggregates of Ag, less for Rb, lowest for Au NPs. The optimal Ag NPs aggregate was estimated for best LEF enhancement per hypothetical REI. Simulated aggregates of Rb containing NPs demonstrated strong LEF, shifted in a wide range.

Engineering Phase Separation in Niobate Glass through Ab Initio Molecular Dynamics for Enhanced Energy Storage Performance and Unprecedented Thermal Stability in Niobate-Based Glass Ceramics.

The advancement of lead-free glass ceramics (GCs) possessing appropriate energy storage characteristics is crucial for the renewable energy and electronics industry. In this study, we synthesized lead-free GCs predominantly composed of the tungsten bronze phase, Ba3.3Nb10O28.3. Ab initio molecular dynamics initially reveal nonuniform distribution within the Ba/Nb-O regions in niobite glassy melts, offering valuable insights for the subsequent crystallization process. The proposal of a B-site engineering strategy is suggested, which entails the concurrent reduction of grain size and augmentation of the band gap in tungsten bronze GCs doped with Ta. This approach results in a substantial enhancement of the dielectric breakdown strength (BDS). Phase-field simulations have indicated that the refinement of grain sizes plays a pivotal role in augmenting the local electric field distribution and breakdown path, thereby contributing to the enhancement of BDS. As a consequence of these modifications, a notably high recoverable energy density (Wrec) of 5.23 J/cm3 can be achieved, accompanied by an ultrahigh efficiency (η) of 94%, and superior thermal stability in energy storage. These outcomes are particularly evident in the case of 2 mol % Ta2O5-doped P2O5-K2O-BaO-Bi2O3-TeO2-Nb2O5 (PKBBTN-T) GCs, where the Wrec and η can be determined to be 2.87 ± 3% J/cm3 and 95.46 ± 4%, respectively, over a temperature range spanning from 20 to 150 °C. Additionally, this specimen exhibits an exceptionally high discharge energy density (Wdis) of 4.01 J/cm3. This comprehensive investigation, comprising experimental and theoretical analyses, establishes an effective pathway and paradigm for the development of dielectric materials with ultrahigh energy storage properties.

Microplastic separation and enrichment in microchannels under derivative electric field gradient by bipolar electrode reactions

The decomposed plastic products in the natural environment evolve into tiny plastic particles with characteristics such as small size, lightweight, and difficulty in removal, resulting in a significant pollution issue in aquatic environments. Significant progress has been made in microplastic separation technology benefiting from microfluidic chips in recent years. Based on the mechanisms of microfluidic control technology, this study investigates the enrichment and separation mechanisms of polystyrene particles in an unbuffered solution. The Faraday reaction caused by the bipolar electrodes changes the electric field gradient and improves the separation efficiency. We also propose an evaluation scheme to measure the separation efficiency. Finite element simulations are conducted to parametrically analyze the influence of applied voltages, channel geometry, and size of electrodes on plastic particle separation. The numerical cases indicate that the electrode-installed microfluidic channels separate microplastic particles effectively and precisely. The electrodes play an important role in local electric field distribution and trigger violent chemical reactions. By optimizing the microchannel structure, applied voltages, and separation channel angle, an optimal solution for separating microplastic particles can be found. This study could supply some references to control microplastic pollution in the future.

P‐N Junction‐Driven Abnormal Electric Field Distribution in the Degraded Multilayer Ceramic Capacitors

Local electric field distribution in the dielectric layer of BaTiO3‐based multilayer ceramic capacitors (MLCCs) is investigated by Kelvin probe force microscopy before and after highly accelerated life test (HALT) degradation combined with the energy band diagram. An unusual electric field concentration phenomenon is directly visualized near the HALT cathode region in the degraded MLCCs while a reverse voltage is applied. Such abnormal behavior is ascribed to the migration of oxygen vacancies within the dielectric layer during the HALT, leading to the formation of a P‐N junction structure and further a heightened barrier under a reverse bias. As a result, a P‐N junctional model is proposed for understanding local failure mechanism of the degraded MLCCs, which enrich the insights into the insulation resistance degradation and the reliability of MLCCs.

Analytical modelling of the transport in analog filamentary conductive-metal-oxide/HfOx ReRAM devices.

The recent co-optimization of memristive technologies and programming algorithms enabled neural networks training with in-memory computing systems. In this context, novel analog filamentary conductive-metal-oxide (CMO)/HfOx redox-based resistive switching memory (ReRAM) represents a key technology. Despite device performance enhancements reported in literature, the underlying mechanism behind resistive switching is not fully understood. This work presents the first physics-based analytical model of the current transport and of the resistive switching in these devices. As a case study, analog TaOx/HfOx ReRAM devices are considered. The current transport is explained by a trap-to-trap tunneling process, and the resistive switching by a modulation of the defect density within the sub-band of the TaOx that behaves as electric field and temperature confinement layer. The local temperature and electric field distributions are derived from the solution of the electric and heat transport equations in a 3D finite element ReRAM model. The intermediate resistive states are described as a gradual modulation of the TaOx defect density, which results in a variation of its electrical conductivity. The drift-dynamics of ions during the resistive switching is analytically described, allowing the estimation of defect migration energies in the TaOx layer. Moreover, the role of the electro-thermal properties of the CMO layer is unveiled. The proposed analytical model accurately describes the experimental switching characteristic of analog TaOx/HfOx ReRAM devices, increasing the physical understanding and providing the equations necessary for circuit simulations incorporating this technology.

Molecular dynamics simulation on electrohydrodynamic atomization: Stable dripping mode by pre-load voltage

Abstract The electrohydrodynamic atomization (EHDA) process is a method of forming liquid droplets or jets in a solution under an electric field. Molecular dynamics simulations were used in this study to reveal the EHDA dripping mode at a microscopic level. In this study, we investigated whether a liquid contains ions under the influence of a 1 V·nm−1 electric field that affects the dipole direction of water molecules to explore the cause of the dripping mode. It was hypothesized that the presence of ions would disrupt the local electric field distribution, causing liquid rupture. Furthermore, we observed the jetting behavior under varying ion concentrations and identified jetting instability. To solve this problem, the pre-load voltage method was used to control the distribution of ions in the solution, thus effectively increasing the ion concentration at the nanotube opening. In this study, we also investigated the movement behavior of ions in solution under different pre-load voltages, leading to a stable dripping mode under different ion concentrations. This study offers microscale mechanism research perspectives for EHDA and can be used in future studies for parameter setting and optimization.

Tuning defect chemistry of vertical graphene arrays toward highly stable and dendrite-free sodium metal anodes

Vertical graphene (VG) arrays, characteristic of particularly porous microscopic structures, are one promising host to accommodate Na deposition, relieve the formidable volume change and eliminate uncontrolled dendrite growth, by decreasing the local current density. However, in practice, the prepared VG arrays possess superabundant defect sites in the local tip positions, which would guide the accumulation of rampant Na-ion flux concentration on these tip defect sites, and thus result in strong local electric field distribution and the divisional dendritic growth. Herein, a novel reconstruction strategy is proposed to re-build the edges and stacking of VG, by removing some unstable carbon defects and changing turbostratic stacking structure of VG to a Bernal stacking mode of the graphited VG, which enables to guide the comparatively smaller and stable interface with Na. Benefiting from the synergistic effect of microscopic structure and defect chemistry design, the re-build VG achieves a long-term reversible Na plating/stripping over 6400 h at an areal capacity of 8 mAh cm−2 in half cell, as well as a long cycle life of up to 3300 h at 1 mA cm−2 with a plating capacity of 4 mAh cm−2 in symmetric cells. Concomitantly, the density functional theory calculations demonstrate that Na atoms tend to nucleate and grow into lateral Na plating on the re-build VG arrays at an atomic level. As a result, the full cell coupled with a P2-Na2/3Ni1/3Mn1/3Ti1/3O2 cathode has a predominant improved cycling stability. This microscopic structure/defect chemistry engineering strategy provides new insight into guiding the uniform deposition of Na metal for high-performance sodium metal battery.

Boosting energy storage performance in negative temperature coefficient linear-like dielectrics via composite modulation in the superparaelectric state

Developing dielectric ceramics with both negative temperature coefficient of capacitance (NTCC) and excellent energy storage performance is beneficial to obtain multifunctional dielectric ceramic capacitors. An effective strategy of composite modulation in the superparaelectric (SPE) state is proposed in BaTiO3-BaZrO3-CaTiO3 (BT-BZ-CT) system to achieve the above two points. The simultaneous addition of BZ and CT to BT ferroelectrics can move the SPE state to the normal use temperature zone and the NTCC characteristic with enhanced energy storage performance can be obtained; and the intentional precipitation of CT at grain boundaries can refine the grain size, increase the bandgap, and strengthen the local electric field distribution as well, thus enhancing the breakdown electric field (Eb). Benefiting from these features, EIA class I-R3L code NTCC together with a high Wrec (∼3.46 J/cm3) and η (90.8%) were achieved in 20BT-40BZ-40CT system, providing a paradigm for building NTCC dielectric materials with high energy-storage performance.

Analysis of local vs. macroscopic properties of porous BaTiO3 ceramics based on 3D reconstructed ceramic microstructures

In the present work, ferroelectric BaTiO3 ceramics with variable porosity level (96%, 89%, 81%, and 74% relative densities) and anisotropy derived from the deformation of sacrificial soft polymeric additives during the pressing step, are investigated by an experimental-numerical approach. 3D micro X-ray computed tomography experimental data with specific numerical procedures are firstly used to reconstruct the 3D microstructures of the porous ceramics and to extract geometrical information concerning the samples. These 3D microstructures are then employed as input in FEM models, in order to determine the local electric field and potential distributions inside the ceramic, with the final aim of evaluating low field effective dielectric permittivity and high field ferroelectric switching P(E) features as a function of porosity and field direction. The dielectric and ferroelectric properties derived by using this procedure are discussed in comparison with experimentally determined ones. The paper demonstrates the usefulness of analyzes and simulations of properties at different lenghtscales based on real 3D microstructures, in such ceramic systems, in completing the understanding of the complex relationship between composition – microstructure – local/macroscopic properties.

Composition-Driven Polarization Distribution in Poly(vinylidene fluoride)-Based Copolymer Blends for High Power Density Capacitors

High power density capacitors have been highly demanded in modern electronics and pulsed power systems. Yet the long-standing challenge that restricts achieving high power in capacitors lies in the inverse relationship between the breakdown strength and permittivity of dielectric materials. Here, we introduce poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) into the host poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to produce PVDF-based copolymer blends, resulting in composition-driven 0-3 type microstructures, featuring nanospheres of P(VDF-TrFE) lamellar crystals dispersed homogeneously in a P(VDF-HFP) matrix together with crystalline phase evolution from the γ-phase to the α-phase. At the critical composition, the TrFE/HFP mole ratio is equal to 1, and the blend film achieves maximum energy storage performance with discharged energy density (Udis) ∼ 24.3 J/cm3 at 607 MV/m. Finite element analyses reveal the relationship between microstructures, compositions, and the distribution of local electric field and polarization, which provide an in-depth understanding of the microscopic mechanism of the enhancement in energy storage capability of the blend films. More importantly, in a practical charge/discharge circuit, the blend film could deliver an ultrahigh energy density of 20.4 J/cm3, i.e., 88.3% of the total stored energy to 20 kΩ load in 2.8 μs (τ0.9), resulting a high power density of 7.29 MW/cm3, outperforming the reported dielectric polymer-based composites and copolymer films in both energy and power densities. The study thus demonstrates a promising strategy to develop high-performance dielectrics for high power capacitors.

Ion thruster accelerator grid erosion mechanism under extreme conditions of cylindrical erosion and chamfer erosion

In this paper, the abnormal experimental phenomenon on barrel erosion under extreme working conditions in the ultra-long life experiment (>10000 h) of ion thruster ion optics is studied by the Immersed-Finite-Element Particle-In-Cell Monte-Carlo-Collision (IFE-PIC-MCC) method and the grid erosion evaluation model. The transport process of beam ions and Charge Exchange (CEX) ions in the grid system, and the characteristics and mechanisms of the aperture barrel erosion under extreme erosion conditions (i.e. the cylindrical erosion and chamfer erosion) were systematically studied. Thanks to the advantage of the IFE method for dealing with complex boundaries in structured mesh, the aperture barrel erosion morphology of the accelerator grid is reconstructed accurately based on the experimental results. The results show that, with the evolution of working conditions, the mechanism of the aperture barrel erosion changes significantly, which relies heavily on the accelerator grid morphology. The change of the accelerator grid aperture barrel morphology has a significant effect on the behavior of CEX ions, and only affects the local electric field distribution, but has no effect on the upstream plasma sheath. As the erosion progresses, the erosion position moves downstream along the grid aperture axis direction, and the erosion range becomes narrower. Regardless of the erosion phase, the erosion rate of the CEX ions located downstream of the decelerator grid is the largest. The erosion rate is related to the mean incident energy and angle, and their variation is closely related to the position and trajectory of CEX ions.

A Stable Solid Polymer Electrolyte for Lithium Metal Battery with Electronically Conductive Fillers.

Electronic conduction in solid-polymer electrolytes is generally not desired, which causes leakage of electrons or energy loss, and the electronically conductive domains at electrode-electrolyte interfaces can lead to continuous decomposition of electrolytes and shorting issues. However, it is noticed in this work that in an insulating matrix, the conductive domains at certain aspects could also have positive effects on the electrolyte performance with proper control. This work evaluates the limitation and benefits of electronically conductive domains in a solid-polymer electrolyte system and discusses the approach to improve the electrolyte physicochemical properties with densified local electric field distribution, enhanced bulk dielectric property, and charge transfer. By deliberately introducing the conductive domains in a regular solid-polymer electrolyte, stable cycle life, low overpotential, and promising full cell performance could be achieved.

A Stable Solid Polymer Electrolyte for Lithium Metal Battery with Electronically Conductive Fillers

AbstractElectronic conduction in solid‐polymer electrolytes is generally not desired, which causes leakage of electrons or energy loss, and the electronically conductive domains at electrode‐electrolyte interfaces can lead to continuous decomposition of electrolytes and shorting issues. However, it is noticed in this work that in an insulating matrix, the conductive domains at certain aspects could also have positive effects on the electrolyte performance with proper control. This work evaluates the limitation and benefits of electronically conductive domains in a solid‐polymer electrolyte system and discusses the approach to improve the electrolyte physicochemical properties with densified local electric field distribution, enhanced bulk dielectric property, and charge transfer. By deliberately introducing the conductive domains in a regular solid‐polymer electrolyte, stable cycle life, low overpotential, and promising full cell performance could be achieved.

Optical Enhancement by Gold Nanoring-Nanodisk Plasmonic Structures for Light Sensing Applications

We design and numerically model a 3D nanoring-nanodisk structure and evaluate the effect of the ring and the disk radii size within the presented structure on optical enhancement. Nanoring-nanodisk is a powerful structure for enhancing the local electric field for photo-sensing applications. We present an enhanced local electric field from the UV to IR wavelength range using the proposed structure with a fixed nanogap. It shows a strong dependence on the disk radius of the structure. In addition, two distinct peaks have different plasmonic vibrational modes appearing in the spectrum. These modes are revealed by 3D surface charge and local electric field distributions. Moreover, our calculations reveal that a smaller disk radius with a larger ring radius can generate more optical enhancement.

Electrodeposited 3D lithiophilic Ni microvia host for long cycling Li metal anode at high current density

The uneven deposition of Li metal is the main reason leading to Li dendrite growth, dead Li formation and infinite volume change, shortening the Li metal battery lifetime and causing catastrophic safety hazards. The widely studied 3D micro-nanostructured lithiophilic Li metal anode hosts can suppress the Li dendrite growth, however, it could barely endure high-rate cycling due to the exacerbated uneven deposition of Li metal at a high current density. Herein, we report an electrodeposited 3D microvia structured lithiophilic Ni skeleton on planar Cu with a nanoscale surface roughness as Li metal anode current collector. The high specific surface area and nanoscale rough surface can achieve both low local current density and uniform electric field distribution, which contribute to the even deposition of Li metal at a high current density. Additionally, the in-situ formed Ni(OH)2 thin layer during electrodeposition is lithiophilic, which could induce the uniform Li nucleation. This 3D lithiophilic Ni microvia (3D NMV) host endow the Li metal anode with long cycling performance for over 830 cycles at an ultra-high current density of 10 mA cm−2. Our work illustrates the synergic effect of 3D structure and surface flatness in achieving high-rate cycling performance.

Effects of Nanofibers Orientation and Aspect Ratio on Dielectric Properties of Nanocomposites: A Phase-Field Simulation.

Polymer-based dielectrics with high energy storage density are attracting increasing attention due to their wide applications in pulsed-discharge and power conditioning electronic fields. Despite some numerical simulation about effects of horizontally arranged and vertically arranged fibers on dielectric properties of composites already studied, the influence mechanism of the specific orientation and aspect ratio still remains to be studied. In this work, the effects of orientation angles and aspect ratios of nanofiber fillers on breakdown behavior and dielectric properties of composites are theoretically analyzed by the finite element and phase-field method. The results show that the more inclined the nanofiber fillers is, the higher the nominal breakdown strength is, which benefits from the obstruction of the conductive channels by the nanofibers. However, the dielectric constant shows the opposite law, which is the result of the decreased polarization along the electric field direction of the nanofiber fillers. Besides this, by modulating the distribution of local electric field, a higher aspect ratio of nanofiber fillers helps to achieve a much higher breakdown strength with a slight sacrifice of dielectric constant. The present work provides a comprehensive and quantitative understanding of the orientation and aspect ratio of nanofiber fillers on the dielectric and breakdown properties of composites, providing important guidance on optimizing the energy storage performance.

Greatly enhanced discharged energy density and efficiency of BiFeO3-Based ceramics by regulating insulation performance

BiFeO3 (BFO) with excellent intrinsic polarization (Ps > 100 μC/cm2) receives a great deal of attention for advanced lead-free ferroelectric materials. However, the low resistance and high leakage current density in its naturally seriously hinder the improvement of energy storage performances. Herein, we demonstrate that superb comprehensive performances of large discharged energy density (Wrec ∼ 6 J/cm3) along with superior discharged efficiency (η ∼ 90%), impressive frequency stability (1–500 Hz), fatigue resistance testing (1-105 cycles) and ultrafast discharged time (t0.9–0.08 μs) could be attained in 0.3BiFeO3-0.7(0.88BaTiO3-0.12Bi(Li1/3Hf2/3)O3 [BFO-(BT-BLH)] relaxor ferroelectric ceramics. Remarkably improved breakdown strength (Eb) of BFO-based solid solutions could be primarily contributed to the substitution of BT-BLH, which provides refined grain sizes, as well as increased bandgap, resistivity, and activation energy. The phase-field simulations further indicate that the refined grain sizes are beneficial to improving local electric field distribution and breakdown path, resulting in enhanced Eb. The uncovered BFO-based ceramics design method provides a platform for high-performance capacitors development for extreme conditions.