Transmission coefficient and energy distribution of electrons emitted from M-I-M thin film structures

A simple model of the electron emission from M-I-M structures with insulator thickness >10 nm has been developed. The electric field distribution inside the insulator is supposed to be inhomogeneous with a region of a high field intensity near the cathode. The dependence of the transmission coefficient and of the parameters of the energy distribution on the applied voltage and on the insulator thickness is calculated. It is shown that features obtained experimentally, which contradict earlier theories, can be explained.     

Cloaking magnetic field and generating electric field with topological insulator and high permeability material

Topological insulator is a new state of quantum matter. When applied magnetic field is applied on a topological insulator, not only the magnetic field is induced, but also the electric field is induced, vice versa. We designed bi-layer magnetic cloak with topological insulator and high permeability material (HPM), derived the electric field and magnetic field inside and outside the bi-layer topological insulator and HPM. Calculation and simulation results show that the applied magnetic field is cloaked by the bi-layer topological insulator and HPM, and the uniform electric field is induced in the cloaked region.     

Experimental observation of negative differential characteristic of corona discharge in ultraviolet spectrum

Corona discharge is a self-sustained discharge which appears at electrodes with a small radius curvature in gas insulation. An almost invisible glow occurs just above the inception voltage. Corona phenomenon is mainly used in electro-technological processes to obtain space charge for electrostatic precipitation, separation of different particles, electrostatic liquid or solid coating, neutralization of space charge, etc. All of these processes rely on a strong nonhomogeneous electric field generated by a point – plate electrode system. When the critical value of the applied voltage is reached, the ionization processes near the point electrode start and give rise to the current between two electrodes. If the pointed electrode is positive, it is possible to observe an anomaly of the current – voltage (I-U) characteristic for the point-plate space. It means that while the voltage is raising the current density decreases in a narrow voltage area (2–3 kV). The anomaly was technically named as negative differential conductivity (dI/dU < 0). Unstable current can have a negative influence on electro-technological processes. The anomaly was detected for different shapes and materials of the electrode as well as for various temperatures and distances between electrodes. An oxidation layer, which appears on the metal electrode, also influences the ionization processes near the pointed electrode and causes a decrease of a current. In this paper measuring of the discharge activity in a point – plate electrode system is presented. Ionization of gas atoms and molecules in a high electric field and the following recombination of electrons and positive ions in the corona region can give rise to high-energy photons which produce new electrons in the field of discharge. Corona discharges are detected by DayCor Corona camera which can register UV emission generated by corona in a day light. The experiment was conducted with various shapes of the pointed electrode and distances between the high voltage and the grounded electrode under applied direct voltage with positive and negative polarity.     

Influence of charge deposition in a field-emission display panel

Field-emission displays (FEDs) have been studied intensively in recent years as a candidate for flat-display panels in the future. In a FED, electrons emit from field emitters. Some electrons may impinge on the insulator surface between cathode and gate electrodes and cause charging of that surface because the yield of secondary electron emission is usually not equal to one. The charging of the insulator walls between cathode and gate electrodes is one of the important factors influencing the performance of a FED. In this paper, a simulation program is used to calculate this charge deposition, electric field distribution and electron trajectories. From the change of the electric field upon charge deposition in the triode region, it is shown that the insulator surface is negatively charged at a low gate voltage, e.g. 20 V. However, positive charge is deposited when the gate voltage is high, e.g. 100 V. The simulations also show that the emission current will increase even further after coating the dielectric with a thin film of a material with a high-secondary emission coefficient such as MgO. If a cone-shaped dielectric aperture is used in a triode, the emission current will decrease after charge deposition. However, the focus performance of the electron beam is improving in this case.     

瞬态光电流对有机薄膜光伏器件中肖特基接触的研究

制备了结构为氧化铟锡(ITO)/有机半导体/金属的有机薄膜光伏器件,电流--电压曲线显示其具有整流特性但有机半导体和电极间肖特基接触的内建电场方向很难判定.为了研究有机半导体和电极的肖特基接触特性,分别制备了结构为ITO/有机绝缘层/有机半导体/金属和ITO/有机半导体/有机绝缘层/金属的器件,通过调制激光照射下器件的瞬态光电流方向可容易判断有机半导体和电极间肖特基接触的内建电场方向,外加偏压下瞬态光电流的强度变化进一步证实了判断的正确性.     

Modulating the bandgaps of graphdiyne nanoribbons by transverse electric fields

The effect of external transverse electric fields on the bandgaps of graphdiyne nanoribbons is investigated from first-principles calculations. The giant Stark effect is observed in the ribbons. When the field is applied, the valence and conduction band edge states are found to be strongly localized at low and high potential edges of the ribbon, respectively. Due to the wavefunction localization, the bandgap decreases with increasing field strength, and a semiconductor-metal transition occurs below a threshold field value. It is also shown that the bandgap decreasing rate depends linearly on the ribbon width. The tunable bandgap of a graphdiyne nanoribbon under an electric field would be helpful for practical applications.     

Study of fast switching processes due to electric and magnetic fields-an NMR approach

Solid state NMR techniques have been developed to investigate dynamic molecular effects (e.g., molecular reorientations) due to simultaneously applied external electric fields on electrically sensitive materials such as liquid crystals (LC), liquid crystalline polymers (LCP) and polymeric electrets. Such effects can be observed only on relatively thin systems (10-200 μm). That means that many scans are necessary to achieve a sufficiently high signal-to-noise-ratio in the spectra (500-1000 scans). If the material is also magnetically sensitive, the electric field can be used to orient molecules in a starting orientational state and by switching-off the voltage to access fast reorientation processes in the magnetic field B₀. Until now, the behaviour of orientable molecular systems under the influence of electric fields has been investigated by means of a more or less quasistatic approach (LCP: 100 V, electrets: 1 kV) in equilibrium states. The achievable time resolution depends on the desired signal-to-noise-ratio. For the case of proton NMR this means a time resolution of about 10 min. However, very often switching processes occur on a much shorter time scale. Using conventional techniques it is impossible to observe fast (ca. 100 μs) electrically or magnetically induced reorientation processes. In this work, we present a concept to overcome the problems outlined above and to extend the area of our current in situ NMR investigations on thin electrically-switched or poled polymeric layers. The basic idea is to include synchronized electric pulses during the NMR experiment using the preparation and/or mixing periods of a 1D or 2D pulse sequence for the application of an orienting field (electric or magnetic) and to use the reversibility of the molecular switching phenomenon to achieve a sufficient signal-to-noise-ratio. The techniques extend the range of possible investigations from about 100 μs to approximately T₁ for correlated spectra (and to longer times of applied fields for uncorrelated spectra). Results are shown for a nematic LC and a nematic polymer having a similar side chain.     

Use of a liquid-metal cathode in high-vacuum studies of electric breakdown

Studies of electric breakdown in a high vacuum involving liquid-metal (mercury and gallium) cathodes, whose surfaces are stabilized by centrifugal forces, have shown that an increase in the angular velocity at which the experimental apparatus rotates causes an increase in the breakdown field; the mechanism for the vacuum breakdown is found to be independent of the voltage across the electrodes. According to the Frenkel theory, vacuum breakdown results from a disruption of the steady state on the liquid-cathode surface in an electric field. Drops of liquid metal on the anode degrade the dielectric properties of the vacuum gap. Under these conditions, the breakdown mechanism becomes dependent on the voltage across the electrodes. Oxide films on the cathode surface also degrade the dielectric properties of the vacuum gap. It is suggested that the dielectric may be charged by positive ions emitted from the cathode.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, Vol. 12, No. 4, pp. 44–49, April, 1969.     

Volume-Charged Cones on a Liquid Interface in an Electric Field

In this study, we explore a novel type of slender conical liquid meniscus arisen in high electric field, which carries surface charge and net bulk charge of opposite sign. Stability of such dissipative structure is ensured by the balance between capillary and electrostatic forces and competition between the surface and bulk electric currents. The bulk charge is governed by the applied voltage being generated by the electric field of the cone due to dissociation/associations reactions at its apex. The effect of the physical parameters of the liquid on the microcone structure is elucidated. It is shown that the cone angle cannot exceed a critical value, which is a function of dielectric permittivity of the liquid. The electric current through the cone is found to be proportional to the square of the applied voltage. The obtained results can be applied for analysis of atomization processes of various liquids.     

Distribution and amplification of an electric field in ferroelectric-dye heterostructures

The distribution of an electric field has been investigated in Langmuir-Blodgett thin-film heterostructures prepared by sequentially transferring layers of the ferroelectric copolymer poly(vinylidene fluoride-trifluoroethylene) P(70% VDF 70% ?C30% TrFE) and the azo dye. An alternating-current voltage applied to the electrodes is unevenly distributed across layers of the dye and the copolymer in accordance with a constant induction along the normal to the heterostructure. The electric-field-induced shift of the absorption spectrum of the dye serves as a probe of the electric field and reveals a noticeable amplification of the electric field in the dye layers (by a factor of 2?C7). The electric field in the ferroelectric is directed opposite to the direction of the electric field applied to the electrodes of the heterostructure.     

Optical fiber sensor for the measurement of electric field intensity and voltage (OPSEF)

An optical fiber sensor for measuring high electric field intensity and voltage, which utilizes the electro-optic effect of bismuth silicone oxide single crystal, has been developed successfully, and the fundamental characteristics have been evaluated. The electric field intensity distribution inside the coaxial electrodes has been measured with this sensor. The measured results are in agreement with the theoretical values.     

Magnetic field effects on the electric modulus properties of nematic mixture E7

The molecular dynamics of the homogeneously aligned nematic liquid crystal mixture E7 subject to a magnetic field has been studied. The dielectric spectra study has revealed a low bias magnetic field effect on the evolution of dielectric relaxation spectra occurred at lower (∼kHz) (δ-relaxation) and higher (∼MHz) (α-relaxation) frequency regions. The complex electric modulus, which converted from experimental dielectric spectra, has been analyzed with theoretical model of Debye relaxation. The obtained fitting parameters of relaxation time and strength of dielectric components are shown to vary systematically with the strength of applied magnetic field. A microscopic molecular dynamic model has been proposed to describe the two-step variation of E7 molecular under the bias magnetic field. The results provide implication for magneto-modulation of liquid crystal molecular dynamics under the bias magnetic field.     

Dynamic behaviors of ferroelectric liquid crystal molecules under an applied electric field

The dynamic changes in ferroelectric liquid crystal (FLC) molecular alignments under an applied electric field are examined by observing the formation of conoscopic figures with a time resolution of 0.1 ms. Close agreements between observed and simulated conoscopic figures under low voltage (30 V) were obtained. Under high voltage (120 V), however, the observed conoscopic figures became blurred between 0.8 ms and 1.1 ms after reversal of the electric field. The light scattering producing the blurriness occurred due to the development of fast transient molecular alignments during the switching transition above the applied voltage 70 V.     

Electroforming and electric breakdown of a thin-film MIM system

The influence of the voltage polarity and also the thickness and material of the upper electrode on the electroforming and breakdown of a thin-film MIM system has been investigated. It is shown that the processes in the insulator in the breakdown and forming have the same nature. On the basis of the experimental results it is concluded that the main factors which distinguish the forming from the breakdown are the magnitude of the energy deposition on the formation of a discharge channel in the insulator and the nature of the gas release from the discharge channel. These determine the geometrical sizes and morphology of the defects formed in the MIM system under the influence of the voltage and are in the one case formed channels and in the other breakdown channels.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 58–63, January, 1992.     

风沙流对高压绝缘子电位和电场分布的影响

研究风沙流对高压绝缘子电位和电场分布的影响,基于有限体积法建立绝缘子风沙气固两相流模型和风沙天气下绝缘子的风-沙-电耦合场模型,计算不同风沙天气下绝缘子表面沙尘的空间分布和沉积及其对绝缘子沿面电位和电场的影响,结果表明：风沙天气下绝缘子沿面电位和电场畸变受风速和粒径影响显著,电位的畸变幅度随风速和粒径的增加而升高,电场的畸变幅度随风速和粒径的增大而减少;风沙天气下绝缘子表面不同的沙尘空间分布和沉积导致绝缘子不同位置沿面电位和电场畸变不同.     

Electrical Properties of Nanostructured Magnetic Colloid and Influence of Magnetic Field

We investigate the electrical properties of the nanostructured magnetic colloid without and with magnetic field. The competition between the directional motion of the charged magnetic nanoparticles and other minor nonmagnetic impurities （also small amount of ions） under applied voltage and their random orientation due to thermal activation is implemented to elaborate the electrically conduction mechanism under zero magnetic field. Two equivalent electric circuits are employed for explaining the charging and discharging processes. The tunnelling conduction mechanism upon application of externally magnetic field may exist in the nanostructured magnetic colloid. The alternation of the two conduction mechanisms accounts for the current spikes when the magnetic field is switched on or off. This work presents the peculiar electrical phenomena of the magnetically colloidal system.     

Effect of electric fields on reattachment and propagation speed of tribrachial flames in laminar coflow jets

The effects of electric fields on the reattachment of lifted flames have been investigated experimentally in laminar coflow jets with propane fuel by applying high voltages to the fuel nozzle. In case of AC, the frequency has also been varied. Results showed that reattachment occurred at higher jet velocity when applying the AC voltages, thus the stabilization limit of attached flames was extended by the AC electric field. Higher voltage and lower frequency of the AC were found to be more effective. On the contrary, the effect of DC was found to be minimal. To understand the early onset of the reattachment with the AC, occurring at higher jet velocity, the influence of AC electric fields on the propagation speed of tribrachial flame edge was investigated during the transient reattachment processes. The propagation speed increased reasonably linearly with the applied AC voltage and decreased inversely to the distance between the flame edge and the nozzle electrode. Consequently, the enhancement in the propagation speed of tribrachial flame edge was correlated well with the electric field intensity, defined as the applied AC voltage divided by the distance.     

The effect of uni/bipolar charge injection on EHD conduction pumping

Electrohydrodynamics (EHD) conduction pumping takes advantage of Coulomb force generated by externally applied electric field and dissociated charges from electrolytes present in the working fluid. With the electric field maintained below the DC breakdown limit (i.e voltage required for charge injection), EHD conduction generated flow relies primarily upon the asymmetry of the electrodes where the flow is always generated toward the specific direction regardless of the electrodes polarity. The charge distribution induced by the process of dissociation may be altered by charge injection, potentially present at the electrodes' surfaces. The charge injection could occur, for example, because of the electrode surface roughness.This paper is a numerical investigation to quantify the impact of the charge injection on the performance of EHD conduction pump. The numerical domain comprises a coplanar asymmetric electrode pair embedded against a 2-D channel wall where the EHD conduction induced liquid flow is expected to be generated from the narrower electrode toward the wider electrode in the absence of charge injection. The electric field, net charge density, and electric body force distributions are presented in the absence and presence of charge injection. In addition, the electrically generated net flow is calculated for several operating conditions.     

Peculiarities of light propagation in chiral liquid crystal cells in an external electric field

We investigate the propagation of the extraordinary ray in a cell with a chiral liquid crystal at oblique incidence. For a 180° twist cell, we study the dependence of the minimum incidence angle at which the light does not yet pass through the cell on the applied voltage. The orientational structure of a liquid crystal in an external electric field has been calculated by directly minimizing the free energy. This has allowed the ray trajectories and the limiting refraction angles to be determined. The results of our calculations are consistent with the experiment. We show that allowance for the electric field nonuniformity in a chiral system is important for agreement between theory and experiment.     

具有L型源极场板的双槽绝缘体上硅高压器件新结构

为了提高小尺寸绝缘体上硅(SOI)器件的击穿电压,同时降低器件比导通电阻,提出了一种具有L型源极场板的双槽SOI高压器件新结构.该结构具有如下特征:首先,采用了槽栅结构,使电流纵向传导面积加宽,降低了器件的比导通电阻;其次,在漂移区引入了Si O2槽型介质层,该介质层的高电场使器件的击穿电压显著提高;第三,在槽型介质层中引入了L型源极场板,该场板调制了漂移区电场,使优化漂移区掺杂浓度大幅增加,降低了器件的比导通电阻.二维数值仿真结果表明:与传统SOI结构相比,在相同器件尺寸时,新结构的击穿电压提高了151%,比导通电阻降低了20%;在相同击穿电压时,比导通电阻降低了80%.与相同器件尺寸的双槽SOI结构相比,新结构保持了双槽SOI结构的高击穿电压特性,同时,比导通电阻降低了26%.