High External Electric Field Research Articles

Polyvinylidene fluoride nanofibers obtained by electrospinning and blowspinning: Electrospinning enhances the piezoelectric β‐phase – myth or reality?

AbstractConsiderable effort has been devoted to improving the properties of PVDF (polyvinylidene fluoride), arguably the most technologically important piezoelectric polymer. Electrospinning has been found to be a particularly effective method of producing PVDF nanofibers with superior piezoelectric properties due to the resulting exceptionally high fraction of the piezoelectrically active crystalline β‐phase. It is typically assumed that the high external electric fields applied during electrospinning enhance the formation of this β‐phase, with the confused literature offering various unsatisfactory mechanistic explanations. However, by comparing PVDF nanofibers produced by two different processes (electrospinning and blowspinning), we show that the electric field is entirely unnecessary; indeed, the crystallization dynamics are principally driven by the applied mechanical stress, as evidenced by structurally identical 200 nm diameter PVDF fibers produced with and without external electric fields.

Enhanced Performance of Perovskite Single-Crystal Photodiodes by Epitaxial Hole Blocking Layer.

Introducing hole/electron transporting and blocking layers is considered to enhance the performance of electronic devices based on organic–inorganic hybrid halide perovskite single crystals (PSCs). In many photodiodes, the hole/electron transporting or blocking materials are spin-coated or thermal-evaporated on PSC to fabricate heterojunctions. However, the heterojunction interfaces due to lattice mismatch between hole/electron, transporting or blocking materials and perovskites easily form traps and cracks, which cause noise and leakage current. Besides, these low-mobility transporting layers increase the difficulty of transporting carriers generated by photons to the electrode; hence, they also increase the response time for photo detection. In the present study, MAPbCl3-MAPbBr2.5Cl0.5 heterojunction interfaces were realized by liquid-phase epitaxy, in which MAPbBr2.5Cl0.5 PSC acts as an active layer and MAPbCl3 PSC acts as a hole blocking layer (HBL). Our PIN photodiodes with epitaxial MAPbCl3 PSC as HBL show better performance in dark current, light responsivity, stability, and response time than the photodiodes with spin-coated organic PCBM as HBL. These results suggest that the heterojunction interface formed between two bulk PSCs with different halide compositions by epitaxy growth is very useful for effectively blocking the injected charges under high external electric field, which could improve the collection of photo-generated carriers and hereby enhance the detection performance of the photodiode. Furthermore, the PIN photodiodes made of PSC with epitaxial HBL show the sensitivities of 7.08 mC Gyair−1 cm−2, 4.04 mC Gyair−1 cm−2, and 2.38 mC Gyair−1 cm−2 for 40-keV, 60-keV, and 80-keV X-ray, respectively.

Effect of external electric field on hydrogen-related defect in amorphous silica

The effect of external electric field on the interaction between interstitial hydrogen atoms and defect-free amorphous silica (a-SiO2) is studied by means of the reactive force field (ReaxFF) molecular dynamics (MD) simulation and density functional theory (DFT) simulation. We investigate the effects of the hydrogen-atom-hopping and the evolution of interstitial hydrogen atom in a-SiO2 on two kinds of hydrogen-related defect, hydroxyl E' center and [SiO4/H]0 center. We find that electric field enhances hydrogen-atom-hopping and the generation of hydroxyl E' center, while does not have significant influence on the formation of [SiO4/H]0 center. Moreover, hydroxyl E' center is more stable under electric field. We note that more unstrained Si-O bonds (shorter than 1.7 Å) become active in the reaction of the interstitial hydrogen atom with a-SiO2 under electric field. These effects of electric field on a-SiO2 lead to an increasing of the hydroxyl E' centers, which gives rise to the degradation in performance of microelectronic devices. These results provide a better understanding of the behaviors of hydrogen atoms and the generation mechanism of hydrogen-related defects in a-SiO2, especially under external high electric field.

Computational Prediction of Novel Ice Phases: A Perspective.

Although computational prediction of new ice phases is a niche field in water science, the scientific subject itself is representative of two important areas in physical chemistry, namely, statistical thermodynamics and molecular simulations. The prediction of a variety of novel ice phases has also attracted general public interest since the 1980s. In particular, the prediction of low-dimensional ice phases has gained momentum since the confirmation of a number of low-dimensional "computer ice" phases in the laboratory over the past decade. In this Perspective, the research advancements in computational prediction of novel ice phases over the past few years are reviewed. Particular attention is placed on new ice phases whose physical properties or dimensional structures are distinctly different from conventional bulk ices. Specific topics include the (i) formation of superionic ices, (ii) electrofreezing of water under high pressure and in a high external electric field, (iii) prediction of low-density porous ice at strongly negative pressure, (iv) ab initio computational study of two-dimensional (2D) ice under nanoscale confinement, and (v) 2D ices formed on a solid surface near ambient temperature without nanoscale confinement. Clearly, the formation of most of these novel ice phases demands certain extreme conditions. Ongoing challenges and new opportunities for predicting new ice phases from either classical molecular dynamics simulation or high-level ab initio computation are discussed.

A hyperbranched polymer with enhanced photorefractive effect at low and zero applied electric field

Organic photorefractive (PR) materials are widely applied in electro-optical technologies. However, most PR materials require a high external electric field to show PR effect, which would cause materials dielectric fatigue and electrical breakdown. It is significant to explore materials that demonstrate high PR effects under low and even zero applied electric field. In this work, through Suzuki polymerization, a hyperbranched conjugated polymeric PR materials is prepared to show high PR effects with coupling gain coefficients (Г values) of 86.3 cm−1 and 62.5 cm−1 at low applied electric field of 2.5 V μm−1 and even 0 V μm−1, respectively, which are superior to the performance of its linear analogue. These results verify the advantages of branched structure in producing high PR effect, providing a new approach for PR material design.

Synthesis of hollow TiO2 nanobox with enhanced electrorheological activity

TiO2 nanoboxes with a hollow interior space, derived from titanium oxydifluoride (TiOF2) nanocubes, were prepared using a two-step method, in which the TiOF2 nanocubes acting as the precursor were first synthesized using a typical hydrothermal route. Subsequently, a second hydrothermal step was developed to prepare the TiO2 nanoboxes. The clear phase transformation from the TiOF2 precursor to anatase TiO2 was confirmed using X-ray diffraction, Fourier-transform infrared spectroscopy, and X-ray photo-electron spectroscopy analyses. The evolution of the morphology from a nanocube to nanobox was revealed by scanning electron microscopy and transmission electron microscopy observations. The influences of the phase and morphology on the electrorheological (ER) effect were investigated using an ER test. The ER results suggested that the ER efficiency was significantly enhanced after the second hydrothermal treatment, especially under a high external electric field strength. The enhancement in the ER efficiency was further studied using a dielectric spectrum analysis. It demonstrated that the faster response time and large permittivity difference obtained from the dielectric spectrum of TiO2 were responsible for the improvement in the ER effect.

Avalanche charge generation in anhydrous glucosides excited by an external electric field

Glycolipids are components of cellular membranes comprising a hydrophobic lipid tail and one or more hydrophilic sugar heads, and are widely associated with the fields of life science and biochemistry. Due to the hygroscopic nature of sugar, the dry thermotropic phases of glycolipids have fewer studies. We report on the electric charge generation in anhydrous glucosides excited by the external high electric field (∼2 MV/m). This causes a large current in the smectic A phase, but not in the isotropic phase. Its intensity is about 100 times larger than the steady state current. The generation of the current was found to be irreversible by the repetition of the field application. The large electric carrier generation is originated in the smectic A phase, possibly due to an electron avalanche breakdown mechanism caused by the collisions of electrons through the impact ionization.

Crystalline growth under electric field: Toward a new route to design domain modulated-structures. Case of CaTiO3

A single crystal of CaTiO3 was prepared by the floating method (FZ) method in which a high external electric field (≥3 kV·cm−1) is applied. Such an electric field is a new powerful tool, in crystalline growth, able to create new chemical structures and original new materials with new physical properties. By varying crystal growth velocity and electric field strength, we show that we can control the macroscopic shape of CaTiO3 single crystals, and we can alter the crystalline orientation of domains. Applying an in-situ electric field during crystalline growth is a new tool to design domain modulated-structures.

Ultrathin Hydrophobic Uhmwpe Membrane for Moisture Sensing and Removal through Water Confinement Effect

Water confinement within the hydrophobic nanopores has attracted intensive research interest recently. Extensive research has been conducted to elucidate the water confinement mechanisms. However, direct measurements of water confinement has been extremely challenging except when high external pressure or electric field were applied. Here we report the unique water confinement effect in a hydrophobic ultrathin and nanoporous ultrahigh molecular weight polyethylene (UHMWPE) membrane. The UHMWPE membrane with thicknesses about 50 nm, consisting of highly aligned interpenetrating fibrous nanoribbons, can rapidly adsorb and confine water molecules when exposed to moist atmosphere of different relative humidity levels. The water confinement effects were characterized systematically using FTIR, TGA-MS and electrochemical impedance spectroscopy (EIS), respectively. The maximum water uptake can reach upto 13 wt%，and conductivity of the film is as high as 50% of that of pure water, which is more than one billion times of that of dry UHMWPE. Molecular dynamics simulation shows that water molecules specifically adsorb to the steps of the aligned PE films around the nanopores, and the adsorbed water clusters form conductive water chains when subjected to external electrical field strengths greater than 0.2 V/nm. The high moisture sensitivity and water confinement property of the film will be of broad applications particularly in moisture sensitive electrocatalysts where the presence of minute amount of moisture might be detrimental to the stability of the electrocatalyst.

Room temperature electrofreezing of water yields a missing dense ice phase in the phase diagram

Water can freeze into diverse ice polymorphs depending on the external conditions such as temperature (T) and pressure (P). Herein, molecular dynamics simulations show evidence of a high-density orthorhombic phase, termed ice χ, forming spontaneously from liquid water at room temperature under high-pressure and high external electric field. Using free-energy computations based on the Einstein molecule approach, we show that ice χ is an additional phase introduced to the state-of-the-art T–P phase diagram. The χ phase is the most stable structure in the high-pressure/low-temperature region, located between ice II and ice VI, and next to ice V exhibiting two triple points at 6.06 kbar/131.23 K and 9.45 kbar/144.24 K, respectively. A possible explanation for the missing ice phase in the T–P phase diagram is that ice χ is a rare polarized ferroelectric phase, whose nucleation/growth occurs only under very high electric fields.

Stable and optoelectronic dipeptide assemblies for power harvesting.

Low biocompatibility or engineerability of conventional inorganic materials limits their extensive application for power harvesting in biological systems or at bio-machine interfaces. In contrast, intrinsically biocompatible peptide self-assemblies have shown promising potential as a new type of ideal components for eco-friendly optoelectronic energy-harvesting devices. However, the structural instability, weak mechanical strength, and inefficient optical or electrical properties severely impede their extensive application. Here, we demonstrate tryptophan-based aromatic dipeptide supramolecular structures to be direct wide-gap semiconductors. The molecular packings can be effectively modulated by changing the peptide sequence. The extensive and directional hydrogen bonding and aromatic interactions endow the structures with unique rigidity and thermal stability, as well as a wide-spectrum photoluminescence covering nearly the entire visible region, optical waveguiding, temperature/irradiation-dependent conductivity, and the ability to sustain quite high external electric fields. Furthermore, the assemblies display high piezoelectric properties, with a measured open-circuit voltage of up to 1.4 V. Our work provides insights into using aromatic short peptide self-assemblies for the fabrication of biocompatible, miniaturized electronics for power generation with tailored semiconducting optoelectronic properties and improved structural stability.

A valence bond study of the activation of methyl halides bonds by electric fields

In the present work, the activation of methyl halides bonds under experience of an external electric field (EEF) is explained from the Valence Bond theory perspective. The dissociation mechanism of C–X bonds (X [Formula: see text] Cl, Br, I) influenced by a homogeneous and a heterogeneous field placed parallel to the bond axis is presented. For all examples, an increase in the electric field strength have similar consequences: (i) the decrease of the energy depth along the dissociation path, (ii) an increase of the equilibrium interatomic distance (at high EEFs), and (iii) the transition from a homolytic to a heterolytic dissociation after some field magnitude. These general behaviors are explained through the curve crossing between the ionic and the covalent structure at some field strength.

Flow characteristics of a microjet arising in an electro-conjugate fluid under a high electric field

ABSTRACTA strong microjet is generated in an electro-conjugate fluid between a positive and a ground electrode in a high external electric field. We here elucidate the mechanism and characteristics of this strong microjet by means of lattice Boltzmann simulations. In this analysis, we assume that charges are injected from the surface of a positive electrode at the position of a locally high concentrated electric field. When the effect of the Coulomb force is much more dominant than the viscous force, a strovnng microjet between the positive and the ground electrode is generated. This microjet attains a maximum velocity, collides with the ground electrode and disperses in oblique directions. The flow rate resulting from the appearance of a microjet increases with increasing electric field strength in a proportional manner. The present numerical results in respect to the visualisation of a microjet are in good agreement with a corresponding experiment.

Перестройка дефектной структуры тетрабората лития (Li-=SUB=-2-=/SUB=-B-=SUB=-4-=/SUB=-O-=SUB=-7-=/SUB=-) во внешнем электрическом поле

The process of the defect structure rearrangement in a lithium tetraborate single crystal under the influence of high voltage external electric field applied along the polar direction [001] is studied with use of X-ray diffractometry. The results are supplemented by measurements of the conductivity kinetics. Under conditions of electric field of 300-500 V/mm strength, a sharp broadening of the 004 reflection diffraction peak and its integral intensity increasing by several times are observed, however its position and shape practically do not change. Under the influence of DC field with a strength in range of 500 to 1500 V/mm, the broadening process slows down, but the rocking curve asymmetry appears as well as its sharp shift to the smaller angles associated with an increase in the lattice parameter along the c-axis. This process is quasi-reversible, since the distorted structure is partially restored at a very slow rate (for several months). Two types of the diffraction peak parameters variation dependencies on the external field are interpreted as the manifestation of two ionic conductivity mechanisms: mobile lithium ions (Li+) at low-intensity electric field and oxygen vacancies (VO2+) at stronger fields. The process of charge carriers’ migration causes the increase of defects concentration and structure changes in the near-surface region of the crystal.

Performance evaluation of an energy meter for low-voltage system monitoring

The paper presents the design, realization and performance evaluation of an energy meter to be installed in LV power networks with specific features to be live-installable, with high accuracy and with high immunity vs. external electric and magnetic fields. The device can be controlled both through Bluetooth and Power Line Communications (PLC) protocols. Such an instrument has been commissioned by some main European utilities for online periodic comparison of energies and powers measured by smart energy meters installed in houses for billing purposes.

Highly durable piezo-electric energy harvester by a super toughened and flexible nanocomposite: effect of laponite nano-clay in poly(vinylidene fluoride)

A highly durable piezoelectric energy harvester is introduced by integrating the toughness and flexibility of a non-electrically poled, laponite nano-clay mineral-induced γ-phase (up to 98%) in a poly(vinylidene-fluoride) (PVDF) matrix by a simple solvent evaporation technique. Owing to a superior electromechanical coupling effect, PVDF/laponite nanocomposites retain excellent biomechanical energy harvesting capabilities under external vibration (as high as 6 V output voltage and 70 nA output current under a compressive force of 300 N) and charge storage properties under an external high electric field (maximum of discharged energy density at a breakdown strength of 302 MV m−1). As a proof of concept, the fabricated nanogenerator (NG) possesses a high output power density (~6.3 mW m−2) that directly drives several consumer electronics without using any storage system or batteries. It paves the way for potential applicability in next generation electronics, particularly as a self-powered device and to configure sustainable internet of things (IoT) sensor networks.

Plasma anisotropy around a dust particle placed in an external electric field.

A self-consistent model of plasma polarization around an isolated micron-sized dust particle under the action of an external electric field is presented. It is shown that the quasineutral condition is fulfilled and the formed volume charge totally screens the dust particle. The ion focusing and wake formation behind the dust particle are demonstrated for different ion mean free paths and the external electric fields. It is obtained that at low values of the external electric field the trapped ions play the main role in the screening of the dust particle charge. For high external electric fields, the density of trapped ions decreases and the dust particle is screened mainly by the free ions.

Unsteady viscous flow driven by the combined effects of peristalsis and electro-osmosis

Electrokinetic transport of fluids through microchannels by micro-pumping and micro- peristaltic pumping has stimulated considerable interest in biomedical engineering and other areas of medical technology. Deeper elucidation of the fluid dynamics of such transport requires the continuous need for more elegant mathematical models and numerical simulations, in parallel with laboratory investigations. In this article we therefore investigate analytically the unsteady viscous flow driven by the combined effects of peristalsis and electro-osmosis through microchannel. An integral number of waves propagating in the microchannel are considered as a model for transportation of fluid bolus along the channel length. Debye-Hückel linearization is employed to evaluate the potential function. Low Reynolds number and large wavelength approximations are employed. Closed-form solutions are derived for the non-dimensional boundary value problem. The computations demonstrate that magnitude of electric potential function is increased with a decrease in the thickness of the electrical double layer (EDL). Stronger electric field also decelerates the flow and decreases local wall shear stress. Hydrodynamic pressure is increased with EDL thickness whereas it is suppressed with electric field. Streamline visualization reveals that the quantity of trapped bolus is decreased with increase in EDL thickness and also with higher external electric field.

Operation of a Three-Electrode Reactor With Different Electrode Bias Potential Configurations

The three-electrode plasma reactor for the treatment of polluted gases combines a dielectric-barrier discharge with a remote third electrode, designed to enhance streamer propagation in a relatively large region. In this paper, experimental studies of the electrical magnitudes of the discharge for different electrode bias voltage configurations are presented. Also, the Laplacian electric field distribution in the interelectrode gap is calculated for each configuration. The degradation efficiency of NO in an N2 atmosphere for the different configurations is also reported. It is found that the discharge is generated only for that electrode bias configuration for which the external electric field promotes the streamer propagation across the electrode gap. Also, for a triggered discharge, the reactor efficiency for the removal of NO changes with the different electrode bias configurations. This result can be explained in terms of the electric field intensity. The configuration with higher external electric field improves the number of streamers propagating in the interelectrode gap so that more reactive species generated in the streamers are effectively entrained in the gas flow to be treated.

A DFT study on the elastic and plastic properties of MoS2 nanosheet subjected to external electric field

Molybdenum disulfide (MoS2) may be synthesized in a large variety of forms such as particles, monolayer and multilayers nanosheets/nanotubes, ropes and ribbons. Due to such diversity, several applications can be found for MoS2. In this paper, on the basis of density functional theory (DFT) calculations using the generalized gradient approximation (GGA) with the Perdew− Burke−Ernzerhof (PBE) exchange correlation, the elastic properties including Young's and bulk moduli together with plastic properties of MoS2 nanosheet under external electric field with magnitudes within the range of 0 V/ang–1.5 V/ang are determined. It is demonstrated that up to the magnitude of 1 V/ang, the external electric field has a negligible influence on the bulk modulus of MoS2 nanosheet. However, by applying an external electric field equal to 1.3 V/ang, a significant increase in the value of bulk modulus occurs. Additionally, by applying an external electric field equal to 1.5 V/ang, the bulk modulus decreases suddenly, showing the considerable influence of high external electric field on the bulk modulus of MoS2 nanosheet. Also, it is observed that the first and second critical strains of the MoS2 nanosheet subjected to biaxial strain are smaller than those of the MoS2 nanosheet under uniaxial strain. Furthermore, it is revealed that for the both uniaxial and biaxial loading cases, by increasing the magnitude of external electric field, the stability of MoS2 nanosheet decreases.