Influence Of High Electric Field Research Articles

Novel Raman Spectroscopy Method for Solutions in Uniform, High-Strength Electric Field.

A novel method of measuring the influence of high electric fields on the Raman scattering of fluids is introduced, which can help understand various interactions of a fluid with the high electric field. The microfluidic chip can impose highly controlled, uniform electric fields across the measurement volume with blocked electrodes, eliminating spurious reactions at the electrode surface. The developed methodology and the experimental setup are utilized to examine the effect of the electric field on three of the stretching vibrations of ethanol in water-ethanol mixtures with varying concentrations of ethanol and effective electric fields up to 1.0MV/m. The increase in the electric field is seen to broadly decrease the intensity of Raman scattering due to a decrease in the polarizability of the ethanol molecules. Although this effect is uniform for all water-ethanol mixtures, it reduces in mixtures with high weight-fractions of water because of the already reduced polarizability of an ethanol molecule due to hydrogen bonding. The combined effect of hydrogen bonding and increase in temperature due to the alternating high electric field even results in an increase in the magnitude of peak intensity for relatively low-weight fractions of ethanol.

Rough FTO electrode interface effect upon ferroelectric switching dynamics in Ag/P(VDF‐HFP)/FTO capacitor structures

AbstractRough FTO electrode interface effect upon the characteristic ferroelectric polarization parameters and switching dynamics in Ag/P(VDF‐HFP)/FTO junctions is systematically evaluated by varying electric field amplitude and frequency. Structural and microstructural studies confirm the ferroelectric phase formation of P(VDF‐HFP) on FTO surface. Tilted rectangular P‐E loops have been recorded in the applied fields ranging over 156.25–468.75 MV/m measured between 250 mHz and 5 Hz frequency ranges. Giant saturation of 21.7 μC/cm2 and remnant polarization of 34.9 μC/cm2 has been noted at low frequencies due to the influence of high electric field induced leakage currents. The coercive field, saturation and remnant polarization response with increase in electric field amplitude and frequency of the applied signal are well fitted with classic domain growth model proposed by Kolmogorov‐Avrami‐Ishibashi. A switching time scales of 32.2–693 ms has been observed for forward switching while for backward switching it is noted as 22.1–618.8 ms, when measured at frequencies from 5 Hz to 250 mHz. Furthermore, the tilted P‐E loops are attributed to the excessive leakage currents due to the high surface roughness of FTO bottom electrode.

The Geometry and Charge of the Streamer Bursts Generated by Lightning Rods under the Influence of High Electric Fields

The streamer bursts generated during the initiation and propagation of leaders play an important role in the creation and maintenance of hot discharge channels in air. The most important parameters related to streamer bursts in this respect are the length of the streamer bursts, their lateral extent and the charge associated with them. The lateral extent of the streamer bursts may play a significant role in deciding the path and the tortuosity of the discharge channels of laboratory discharges and lightning. The charges associated with the streamer bursts are needed in understanding the physical processes associated with the streamer-to-leader transition. In this paper, the length, the lateral extension and the charge of the streamer regions generated by grounded conductors when exposed to external electric fields are estimated. This estimation is based on two assumptions: (i) once a streamer is incepted, the streamer head follows the direction of maximum background electric field at the location of the streamer head and (ii) the streamer continues to extend along this direction until the potential drop along the streamer channel matches the potential drop caused by the background electric field between the initial and end points of the streamer channel. The same technique could be used to estimate the streamer bursts generated in laboratory discharges and lightning stepped leaders. It is shown that in estimating the geometry of the streamer region, it is necessary to include the spread of streamers caused by branching. Moreover, the charge associated with the streamer region increases as the frequency of branching increases. The results obtained confirm that the charge in the streamer region can significantly change the potential ahead of the streamer region from the background potential and this has to be taken into account in any study that simulates the initiation and propagation of lightning leaders. Since the streamer bursts of leaders control the direction and speed of the leaders, the technique we have used here could be implemented in lightning leader progression models.

Influence of High Electric Field on Operation of AlGaN/AlN/GaN High Electron Mobility Transistor

Influence of High Electric Field on Operation of AlGaN/AlN/GaN High Electron Mobility Transistor

Study on Charge and Discharge Phenomenon of Lithium Ion Battery under High Electric Field

It aims to clarify the influence of high electric field on lithium ion battery and to contribute to the establishment of appropriate use of it. In this study, a lithium ion battery is installed in the vicinity of a spherical electrode (diameter 100 mm) kept at a direct current ±10 kV and the presence or absence of a voltage change of the lithium ion battery. (1) A gap (20 mm) is provided between a needle electrode (tip radius of curvature 51 μm) attached to the positive electrode of a lithium ion battery and a spherical electrode, and the negative electrode is grounded. When applying +10 kV, the voltage rose by about 15 mV in 300 s, and the lithium ion battery was charged. When −10 kV was applied, the voltage dropped by about 10 mV in 300 s, and it was discharged. (2) A gap (10 mm) is provided between the needle electrode attached to the positive electrode of the lithium ion battery, and the spherical electrode, and the needle electrode attached to the negative electrode, and the grounded spherical electrode (diameter 100 mm). In this case, the lithium ion battery voltage has changed. Therefore, Lithium ion battery was found to be affected by high electric fields. It is presumed that the voltage of the battery changes because corona discharge causes charge transfer in the gap and a chemical reaction of the lithium ion battery occurs.

Effects of high temperature and high electric field on the space charge behavior in epoxy resin for power modules

In this paper, space charge behavior over a large range of electric field and temperature, of two kinds of epoxy resins are investigated using an improved pulsed electro-acoustic method. Significant influence of high electric field and high temperature on the space charge accumulation in epoxy are found. Hetero charge accumulation starts to build up at 80 °C under 120 kV/mm for amine-type hardener cured epoxy (EP-AM), while at 140 °C under 60 kV/mm for anhydride-type hardener cured epoxy (EP-AH). The accumulated charge increases with the increasing of electric field and temperature. The maximum enhancement of local electric field of is 135 and 123 % at 140 °C for EP-AM and EP-AH, respectively. Quantum chemical calculation is performed to clarify the mechanism of space charge characteristics in the two types of epoxy. It is indicated that ionization of remnant unreacted hardener and electrode injection may be the main sources of space charge. The interaction between molecular chains of EP-AH is stronger than that of EP-AM, which makes it have better space charge characteristics even under high temperature.

Anisotropic hole drift velocity in 4H-SiC

A theoretical study on the nonlinear transport of holes in the transient and steady state of p-doped 4H-SiC under the influence of high electric fields is presented. It is based on a nonlinear quantum kinetic theory which provides a clear description of the dissipative phenomena that are evolving in the system. The hole drift velocity and the nonequilibrium temperature are obtained, and their dependence on the electric field strength is derived and analyzed.

Study of Electron Transport in 4H-SiC by Using Nonequilibrium Statistical Ensemble Formalism

A theoretical study, by using Nonequilibrium Statistical Ensemble Formalism (NESEF), on the nonlinear transport of electrons in the transient and steady state of n-doped 4H-SiC under the influence of high electric fields is presented. The electron drift velocity and the nonequilibrium temperature are obtained, and their dependence on the electric field applied in the orientation parallel or perpendicular to the c-axis is derived and analyzed.

Liposomal membrane disruption by means of miniaturized dielectric-barrier discharge in air: liposome characterization

The increasing interest of the plasma community in the application of atmospheric-pressure cold plasmas to bio-specimen treatment has led to the creation of the emerging field of plasma biomedicine. Accordingly, plasma setups based on dielectric-barrier discharges have already been widely tested for the inactivation of various cells. Most of these systems refer to the plasma jet concept where noble gases penetrate atmospheric air and are subjected to the influence of high electric fields, thus forming guided streamers. Following the original works of our group where liposomal membranes were proposed as models for studying the interaction between plasma jets and cells, we present herein a study on liposomal membrane disruption by means of miniaturized dielectric-barrier discharge running in atmospheric air. Liposomal membranes of various lipid compositions, lamellarities, and sizes are treated at different times. It is shown that the dielectric-barrier discharge of low mean power leads to efficient liposomal membrane disruption. The latter is achieved in a controllable manner and depends on liposome properties. Additionally, it is clearly demonstrated that liposomal membrane disruption takes place even after plasma extinction, i.e. during post-treatment, resembling thus an ‘apoptosis’ effect, which is well known today mainly for cell membranes. Thus, the adoption of the present concept would be beneficial for tailoring studies on plasma-treated cell-mimics. Finally, the liposome treatment is discussed with respect to possible physicochemical mechanisms and potential discharge modification due to the various compositions of the liquid electrode.

Neutron diffraction on functional materials under electric field or mech. load

In this contribution neutron diffraction studies on functional materials under special environmenal conditions will be presented. In particular, studies of ferroelectric ceramics under high electric fields as well as shape memory alloys under mechanical load will be highlighted. The investigations were carried out at the high-resolution neutron powder diffractometer SPODI (FRM II / Garching n. Munich) which offers special sample environmenal tools for electric fields, mechanical load etc. In-situ studies on ferroelectrics under the influence of high electric fields enable to establish correlations between the macroscopic poling behaviour and corresponding structural changes. The investigations were carried out on technologically applied lead zirconate titanate based samples and on a bismuth sodium titanate based system. A self-designed device allows the investigation of large bulk samples under different orientations of the electric field. This method allows to analyze the poling mechanisms in technical ferroelectrics, such as piezoelectric effect, domain reorientation and phase transformations. In the system Bi0.5Na0.5TiO3 - BaTiO3 – K0.5Na0.5NbO3 the large recoverable field-induced strain could be attributed to a reversible field-induced phase transition from an almost non-polar, pseudocubic tetragonal phase to a distorted, ferroelectric active phase [1]. Polycristalline monoclinic nickel-titanium shape memory alloys have been investigated under mechanical load to analyze their stress-strain behaviour and to derive the elastic constants. A novel tensile rig allows to orient the load axis in a Eulerian cradle like manner. The elastic constants tensor could be calculated based on a series of diffraction patterns under different sample orientations in the initial state and under 0.6 % strain. Furthermore the contributions of elastic deformation (lattice dilatation) and inelastic deformation (orentation of twins) to the total strain could be separated.

Oxygen vacancy redistribution in PbZrxTi1−xO3 (PZT) under the influence of an electric field

Abstract Oxygen isotope exchange experiments are performed in donor doped PbZr x Ti 1 − x O 3 (PZT) under field load. A detailed mapping of the oxygen tracer ions and thus indirectly of the oxygen vacancy distribution is enabled by spatially resolved time-of-flight secondary ion mass spectrometry (ToF-SIMS). Hence, knowledge can be gained on the oxygen vacancy redistribution under the influence of high electric fields applied to Cu inner electrodes of a PZT multilayer stack. Upon field load an enhanced oxygen tracer concentration is measured near to the cathode and interpreted in terms of a field-driven oxygen vacancy accumulation at an oxide ion blocking Cu cathode. Oxygen tracer depth profiles in near-anode and near-cathode diffusion zones give quantitative information on local grain and grain boundary diffusion coefficients and their dependence on applied voltages.

Numerical Simulation of Formation and Distortion of Taylor Cones

Taylor cones are integral parts in many important applications like electrospinning and electrospray mass spectroscopy. A better understanding of this complex phenomenon of Taylor cone is critical for better control of these processes. As an example, if it is possible to identify and prioritize the roles of fluid characteristics and externally applied electric field, it might be easier to target and control the diameters of nanofibers in an electrospinning process. Under the influence of high electric fields, Taylor cones are formed by a number of liquids including many polymeric solutions. Because of small spatial (microns and below) and temporal (microseconds and below) scales, it is difficult to experimentally study the transient formation of Taylor cones. A number of theoretical analyses have been done under simplifying assumptions like uniform electric field, constant electrohydrodynamic behaviors of the fluid, stationary droplet, etc. Initial Taylor formulation included the introduction of “leaky dielectric” that accumulated charges only on the surface for certain dielectric fluids. Yarin et al. later developed analysis for stationary droplets assuming them to be “perfectly conducting”. To simulate the electrospinning process, the formulation needs the ability to analyze moving boundary conditions, complex fluid properties, three dimensional geometry, and nonlinear coupling between air and liquid, among others. To overcome some of the assumptions of theoretical analyses and as another complementary tool, a computer simulation method was proposed using a commercially available software. In this investigation, much studied aqueous polyethylene oxide (PEO) solution was used to study formation and distortion of Taylor cones. An initial velocity was given to the fluid from the tip of a nozzle and an appropriate electric field was applied to form the Taylor cones. Literature values were used for flow, fluid, and electrical characteristics of the solution. By appropriately manipulating fluid velocities and electric fields, simulations were successful to both replicate the classical cone and distort it to various degrees. These formation and distortion of Taylor cones were similar to reported experimental results. While the numerical and experimental Taylor cones were significantly different in sizes, nondimensional shapes, and sizes of both the results were strikingly similar. Velocities of the fluid in the jet jumped almost 50 times to meters/second as was experimentally observed. Unlike theoretical solutions, the simulation results showed the interaction of the electric fields between the air and advancing fluid tip.

Threshold switching via electric field induced crystallization in phase-change memory devices

Phase-change devices exhibit characteristic threshold switching from the reset (off) to the set (on) state. Mainstream understanding of this electrical switching phenomenon is that it is initiated electronically via the influence of high electric fields on inter-band trap states in the amorphous phase. However, recent work has suggested that field induced (crystal) nucleation could instead be responsible. We compare and contrast these alternative switching “theories” via realistic simulations of device switching both with and without electric field dependent contributions to the system free energy. Results show that although threshold switching can indeed be obtained purely by electric field induced nucleation, the fields required are significantly larger than experimentally measured values.

Electric field induced anomalies in ferroelectricK2SeO4

The lock-in transition of K2SeO4 at 93.2 K was studied using high-resolutionγ-ray diffraction, in situ dielectric measurements and neutron scattering. The phasetransition shows a coexistence regime of 1.0 K with clearly resolved incommensurate andcommensurate satellite reflections. Within a temperature interval of several K above thelock-in transition, strong third order satellites are observed, indicating a pronouncedsquaring of the modulation wave. Under the influence of high electric fields an intermediatephase is observed, which is characterized by a diffuse intensity distribution. Inaddition, the dielectric permittivity exhibits two maxima, indicating the existence oftwo separate phase transitions. This behaviour is attributed to distortions of thediscommensuration lattice and pinning of the discommensurations by accumulatedcharged defects. It seems to be characteristic for modulated ferroelectrics of theA2BX4 group, since a similar behaviour is also found in isostructuralRb2ZnCl4 andK2ZnCl4. The soft-modedynamics close to Tc is found to be essentially independent of the electric field and not affected by thediscommensuration lattice.

Robust charge stripe order under high electric fields inNd1.67Sr0.33NiO4

The influence of high electric fields on the charge stripe order in Nd1.67Sr0.33NiO4 was studied by means of simultaneous hard x-ray diffraction and electrical transport experiments. Direct measurements of the charge stripe satellite peaks in zero and high electric fields provide no evidence for a deformation or a sliding of the stripe lattice, which contradicts previous indications from non-linear conductance effects. By using the order parameter of a structural phase transition for instant sample temperature measurements, non-linear transport effects can be attributed to resistive heating. Implications for the pinning of stripes in the nickelates are discussed.

On the interpretation of some electrical aging and relaxation phenomena in solid dielectrics

Electrical aging and relaxation in solid dielectrics are phenomena studied for decades but still largely poorly understood. The lack of understanding, or sometimes the misunderstanding, are partly due to inadequate or deficient theories and partly due to wrong interpretation of theories or concepts developed for other materials than dielectrics. In addition, a serious analysis of some of the empirical and approximate relationships often used to interpret polymer relaxations reveals that they are not only limited and restrictive but also that they are based on very dubious assumptions. Dry or wet electrical aging is much more complex and often includes many phenomena with synergetic effects such as thermal aging, electrochemical reactions, space charge effects, etc. In this lecture, we intend to show that some of the theories often cited in the literature are wrong or inappropriate. We show why they cannot describe the phenomena at play and we present some alternatives for future work in the domains of relaxation and electrical aging. The relations between aging, space charges and polarization of polyethylene (PE) under the influence of high electrical fields (above 20 kV/mm) are discussed in light of our electrical aging model. It is our contention that strong charge injection occurs only after nanocavity formation, i.e. above the critical field. The amorphous phase is then significantly deformed and weak van der Waals attraction bonds are broken, leading to another faster aging regime. The possible relation between the nanocavity formation at moderate fields and bonds breaking at higher fields proposed in our aging model and various polarization measurements is discussed. One objective of this paper is to encourage the development of more complex and complete theories specific to dielectrics. Some experimental work needed to achieve this goal is pointed out.

Influence of electro-mechanical stress on electrical properties of dielectric polymers

The influence of high electrical fields on water treeing, electrical treeing, relaxation, conductivity and charge mobility in various polymers is reviewed within the context of a molecular model. The real value of the AC field acting on water trees is questioned and it is shown that the strain induced by very large fields may affect the water tree growth in solutions with large dielectric constant. A model based on simple electrostatic and molecular parameters describes most water treeing results. Light emitted during electrical tree growth could be associated with the field-induced strain at the tip of the electrode. The strain in PET is also related to the Maxwell stress due to high DC field. The log of the charge stored in some polymers varies with the square of the field suggesting that there same phenomenon might influence charge formation under high fields. The significance of a constant mobility value is discussed in light of experiments showing that it is not constant at moderate fields in various polymers. It is shown that the only constant parameter under varying high fields is the activation volume typical of a given sample. Future work is pointed out, especially regarding the nature of the trapping sites and the influence of sample size on the activation volume.

Effect of field dependent trap occupancy on organic thin film transistor characteristics

A model to calculate the current voltage characteristics of organic thin film transistors is presented. The model takes into account the influence of high electric field on trap occupancy. The case of the traps at a single energy level is considered in detail. Relevant equations are solved numerically using an iteration method. The field dependent trap occupancy model is found to change free surface charge Qsf and drain saturation current Id significantly. The model is compared with the experimental data published by two different groups. There is good agreement between experimental data and our model.

Influence of high electrical fields on ageing and polarization properties of polyethylene

AbstractThe influence of high electrical fields (above 20 kV mm−1) on ageing, polarization and morphology of polyethylene (PE) is discussed. Infrared and positron annihilation spectroscopy measurements together with capacitance measurements tend to indicate that polymer morphology is modified by high fields. We show that accelerated electrical ageing characteristics of PE are directly linked to morphology changes induced by the field. Below a so‐called critical field, the activation volume of the ageing process is dependent on field‐induced strain. Above the critical field, the amorphous phase is significantly deformed and weak van der Waals bonds are broken, leading to another faster ageing regime. There is excellent agreement between the proposed model and experimental data obtained with PE‐insulated high voltage cables. The possible relation between the submicrocavity formation proposed in our ageing model and various polarization measurements is discussed. It is our contention that strong charge injection occurs only after submicrocavity formation, ie after weak bonds are broken. As is well known, polarization currents obtained under high fields are controlled by space charges. It seems that wave packets and the negative resistance observed above 100 kV mm−1 in PE are associated with a steady state in field‐induced defect formation. This suggests that space charges are related to the formation of submicrocavities and, therefore, are a consequence and not a cause of high field ageing.© 2002 Society of Chemical Industry

Effect of electric fields on the structure of phosphatidyl choline in a multibilayer system

Polarized attenuated total reflection (ATR)-FTIR measurements were carried out on aligned multibilayers of dipalmitoyl phosphatidyl choline (DPPC) under the influence of high electric fields. The electric fields varied from 0 up to 5.5×10 6 V/cm in the hydrocarbon layer and up to 1.1×10 6 V/cm in the polar layer of the aligned multibilayer, when the applied potential across the 1-μm-thick multibilayer plus the 0.5-μm-thick air gap reached the value of 1000 V. At relatively low applied potentials of less than 100 V, when the electric fields in the hydrocarbon and in the polar layer were below 5.5×10 5 and 1.1×10 5 V/cm, respectively, the inhomogeneous field between the two layers is adequate to start driving the polar groups into the hydrocarbon layer, exerting a pressure and penetrating them. This results in distortion of the orientation of the hydrocarbon chains. Only at much higher potentials above 600 and 700 V starts the direct reorientation of the dipoles of the different polar residues by the electric field.