Showing papers on "Electric potential published in 1985"

Plasma potentials of 13.56-MHz rf argon glow discharges in a planar system

Abstract: The plasma potential of 13.56‐MHz low‐pressure argon glow discharges has been measured for various modes of applying the rf power in a geometrically asymmetric planar system. The plasma potential is determined from the energy distribution of positive ions incident on the grounded electrode. The voltages on the excitation electrode (target electrode) are carefully measured and the capacitive sheath approximation is used to relate these measured voltages to the measured plasma potential. This approximation is successful in most of the situations encountered in this low‐pressure (20 mTorr) relatively low‐power density regime. The effects of superimposing dc voltages on the excitation electrode are discussed.

Interplanetary magnetic field control of high-latitude electric fields and currents determined from Greenland Magnetometer Data

Abstract: To determine the effects of the interplanetary magnetic field (IMF) on the electric potential as well as on ionospheric and field-aligned currents, a recently available numerical algorithm is applied to an empirical model of high-latitude magnetic perturbations, parameterized in terms of the By and Bz components of the IMF. The empirical model is derived from 20-min average magnetometer data observed during summer at the chain on the west coast of Greenland and the corresponding IMF information from the HEOS 2 satellite. The calculated results reproduce fairly well overall features of the influence of the IMF on high-latitude electric fields which have been reported on the basis of more direct measurements. This confirms the validity of the numerical method and the conductivity distribution models. In addition, our results indicate that the system of ionospheric and Birkeland currents near the polar cusp, which has been shown to depend strongly on By, exists independently of the system of region 1 and region 2 field-aligned currents, which, on the other hand, depends strongly on Bz. The direction of the field-aligned currents in the dayside polar cap is uniquely controlled by the sign of the By component of the IMF, namely upward currents for By > 0 in the northern polar cap and oppositely directed for By 0 and By small the ionospheric and field-aligned currents are localized near the dayside polar cusp, and the electric field has a dusk-dawn component in a narrow region near magnetic local noon in agreement with reported satellite measurements. The associated distribution of field-aligned currents consists of the region 1 current system and an additional pair of oppositely directed currents located poleward of the region 1 currents.

Pyroelectric conversion cycles

Abstract: The effect of the type of power cycle upon the amount of output electrical work for a pyroelectric converter has been measured. Output electrical energy densities are reported for ceramic lead zirconate modified with Sn4+ and Ti4+ in the execution of a variety of thermal‐electrical cycles. The effect upon the energy density due to changes in the voltage cycle limits and changes in the load resistance were also studied. A conversion cycle which is an electric analog of the Ericsson cycle is shown to yield the largest output energy density (100 mJ/cm3 for a 12.6 K temperature excursion and a 28‐kV/cm electric field excursion).

Generation of positive charge in silicon dioxide during avalanche and tunnel electron injection

Abstract: Avalanche and Fowler–Nordheim tunneling electron injections have been performed at constant current on a broad variety of differently processed Al‐gate metal‐oxide‐semiconductor capacitors. It is found that the same type of positive charge (the ‘‘slow states’’) is generated during low‐field and high‐field electron injection. The maximum amount of positive charge which can be generated at a given electric field depends on processing and increases linearly with the average field in the oxide. However, the rate at which the positive charge is generated is controlled uniquely by the anode field, for a given polarity of the gate voltage. It follows that the role of the electron traps in the bulk SiO2—independent of their nature—is that of increasing both the rate and the total number of created defects by enhancing, respectively, the anode field, as a result of the distortion of the potential in SiO2, and the average field which must be increased to maintain a constant injected current. Processes described ear...

Strong ion acceleration by a collisionless magnetosonic shock wave propagating perpendicularly to a magnetic field

Abstract: A 2 1/2 ‐dimension, fully relativistic, fully electromagnetic particle code is used to study the time evolution of a nonlinear magnetosonic pulse propagating in a direction perpendicular to a magnetic field. The pulse is excited by an instantaneous piston acceleration, and evolves in a totally self‐consistent manner. A large amplitude pulse traps some ions and accelerates them parallel to the wave front. They are detrapped when their velocities become of the order of the sum of the E×B drift velocity and the wave phase velocity, where E is the electric field in the direction of the wave propagation. The pulse develops into a quasishock wave in a collisionless plasma because of dissipation caused by the resonant ion acceleration. A simple nonlinear wave theory for a cold plasma describes the shock properties observed in the simulation except for the effects of resonant ions. In particular, the magnitude of an electric potential across the shock region is derived analytically and is found to be in good agreement with our simulations. The potential jump is proportional to B2, and hence the E×B drift velocity of the trapped ions is proportional to B.

Measurements of initial potential gradient and particle charges in a Montana summer thunderstorm

Abstract: An Aerocommander aircraft made three passes through a small isolated thunderstorm on July 19, 1981. These passes were made at a temperature of −5°C and were in conjunction with other aircraft at different altitudes. The Aerocommander was equipped to measure the vertical component of the ambient potential gradient, particle charge, particle size and character, cloud liquid water content, temperature, and vertical velocity. Evidence is presented for the association of charge with ice particles. The development of the potential gradient in relation to movement of these ice particles is discussed. In general, the highest charge densities, of order −0.5 C km−3, were coincident with regions of high graupel concentration and the highest potential gradients, of order −15 kV m−1, were measured below regions with the highest radar reflectivities. Only a small fraction ( ±5 pC), but these were found even at the earliest stages of electrification. The results are compared to concepts derived from recent laboratory experiments on the charge produced during ice particle collisions.

Model for a glow discharge in flowing nitrogen

Abstract: A two‐dimensional model of the positive column of a glow discharge in flowing nitrogen is presented. The model is applicable to a cylindrically symmetric and axially nonuniform weakly ionized discharge. Nitrogen ionization mainly results from associative ionization occurring in the collisions of metastable molecules in the a’1Σ−u and A3Σ+u electronic states. Gas heating explains the lowering of the electric field as the current increases or the flow velocity decreases. Under most conditions, vibrational deactivation results from superelastic collisions between excited molecules and electrons. Electric field, discharge voltage, vibrational and electronic populations, and gas temperature, are calculated as a function of pressure, flow velocity, diameter and length of the discharge, and current. Quantitative comparisons with available experimental data are made. Good agreement is observed for discharges at low pressures in gas flows with low Reynolds numbers.A two‐dimensional model of the positive column of a glow discharge in flowing nitrogen is presented. The model is applicable to a cylindrically symmetric and axially nonuniform weakly ionized discharge. Nitrogen ionization mainly results from associative ionization occurring in the collisions of metastable molecules in the a’1Σ−u and A3Σ+u electronic states. Gas heating explains the lowering of the electric field as the current increases or the flow velocity decreases. Under most conditions, vibrational deactivation results from superelastic collisions between excited molecules and electrons. Electric field, discharge voltage, vibrational and electronic populations, and gas temperature, are calculated as a function of pressure, flow velocity, diameter and length of the discharge, and current. Quantitative comparisons with available experimental data are made. Good agreement is observed for discharges at low pressures in gas flows with low Reynolds numbers.

High-Field Distribution and Mobility in Semiconductors

Abstract: A first-principles theory of carrier distribution in the presence of an electric field of arbitrary strength, which takes into account the quantum-mechanical field-broadening, is described under conditions that the acoustic-phonon scattering is the dominant mechanism of scattering. The general expression of the mobility so obtained reduces to its Ohmic value for vanishing small electric fields, is a quadratic function of electric field in the warm-electron regime, and varies inversely with the electric field at sufficiently high electric fields (hot-electron regime). A saturation current is obtained in the high-field limit, when electron mobility is limited solely by the field-broadening effect; the saturation velocity being comparable to the thermal velocity of an electron. The hot-electron temperature, defined in terms of average energy of an electron, is equal to the lattice temperature in the Ohmic regime, rises quadratically with the increasing electric field in the warm-electron regime, and rises linearly in the hot-electron regime. These results are in agreement with those of experiments on n-Germanium.

A microscopic model of metal–semiconductor contacts

Abstract: A one‐dimensional local‐density model of the charge density,electrostatic potential, and energetics of metal–semiconductor contacts is constructed. This model is an extension of analogous models of bimetallic junctions to include the gap in the semiconductor excitation spectrum, space charge effects in the semiconductor, and fabrication‐induced charges near the interface. Self‐consistent analysis of the valence‐electron charge redistribution at the model metal–semiconductor interface relative to the corresponding vacuum surfaces reveals a cancellation which makes the height of the rectifying Schottky barrier directly proportional to the observed vacuum work function of the metal in the absence of additional charges induced by atomic relaxations or chemical reactions which occur during the fabrication of the interface. The experimentally observed stability of the Schottky barrier heights against changes is applied bias and semiconductor doping are predicted correctly. The occurrence of interfacial atomic rearrangements and/or chemical reactions is incorporated into the model via the inclusion of charge centers near the interface. Four types of centers are considered: donors, acceptors, and three‐state centers with both positive (U>0) and negative (U<0) effective electron–electron interactions. Applications of the model to describe measured barrier heights on GaSe(0001) and GaAs(110) require approximately 101 4 negative‐U centers per cm2 except in the case of noble metals and Sn on GaSe(0001).

Electric field distributions in strongly coupled plasmas

Abstract: Corrections to the adjustable-parameter exponential (APEX) model recently proposed by Iglesias, Lebowitz, and MacGowan for electric field distributions in a strongly coupled plasma are defined and discussed. The results for a neutral point are compared with those from Monte Carlo calculations for two values of the plasma parameter, and good agreement is obtained.

Charging Dynamics of Dielectrics Irradiated by Low Energy Electrons

Abstract: A recent study by Gross et al. showed the possibility of positive charging of dielectric materials by low energy electron irradiation. In this paper we model the charging process allowing us to predict the voltage builtup or decay and the corresponding charging currents under various initial potential conditions of the dielectric. The model incorporates the secondary electron emission (SEE) yield curve and the energy distribution of the secondaries. The energy distribution is essential to obtain the correct charging behavior for beam energies smaller than the second crossover energy of the SEE yield curve. The results agree, in general, with experimental data Further it is shown theoretically that knowledge of the charging current and the corresponding voltage behavior of an irradiated sample can be utilized to determine the secondary electron yield curve for dielectrics and conductors.

The effect of a resonant electric field on a one-dimensional classical hydrogen atom

Abstract: The authors study the classical motion of an electron moving in a Coulomb potential and a resonant and near-resonant electric field, but constrain the electron to move only in the direction of the field. This simple model of an excited hydrogen atom in a microwave field is simpler to understand than the three-dimensional system, yet retains some essential dynamical features. They show how the Coulomb singularity can be removed by regularisation in order to produce a Hamiltonian suited to efficient numerical computations. They obtain accurate estimates of the field strengths at which ionisation occurs and show that for resonant fields this is well estimated by the second-order resonance-overlap criterion. They show that the frequency dependence of the ionisation probability is similar to that of the classical three-dimensional system and show how its behaviour depends upon particular stable periodic orbits which persist for quite strong fields. They discuss the relevance of this model to the three-dimensional case and to quantal calculations.

Direct indication technique of plasma potential with differential emissive probe

Abstract: We present a new method of plasma potential measurement with a differential emissive probe. The dc heated probes are combined with a feedback loop control circuit to measure plasma potential automatically. In addition, it is shown that connecting to the central point of the filaments reduces the effect on the emissive currents of voltage drops across the filaments. The decay time constant of half‐cycle heated emissive probe current during the off heating cycle is shown to depend on the initial emission current and on the bias voltage.

The electrical potential and the magnetic field of an axon in a nerve bundle

Abstract: A volume conductor model is used to determine the electric potential and the magnetic field associated with a propagating action potential in a single axon which lies off center in a sheathed, anisotropic nerve bundle. The results of the model are interpreted in terms of simple electrical circuits.

Water content and electric potential distributions in gelatinous bentonite sludge with electroosmotic dewatering.

Abstract: To analyze the electroosmotic dewatering process precisely, the variations of water content and electric potential distributions in the sludge are made clear. The distributions of water content and electric potential in gelatinous bentonite sludge with electroosmotic dewatering were studied experimentally under the conditions of both constant voltage and constant electric current. It is proved that the water content distribution is generally related to the electric potential distribution throughout the dewatering process. Electroosmotic dewatering under constant voltage is compared with that under constant electric current. Electroosmotic dewatering combined with vacuum dewatering is also discussed from the viewpoint of these distributions.

Double layer formation caused by contact between different temperature plasmas

Abstract: The formation of an electrical potential difference between hot and cold plasmas is studied by means of a particle simulation. It is found that a double layer structure is formed on the hot‐plasma side of the contact surface between the cold and hot plasmas. The potential difference is given approximately by φDL∼Teh/2e, where Teh and e are the hot‐electron temperature and the electronic charge, respectively. The double layer is accompanied by a negative potential dip on the low potential side (cold plasma) of the double layer, the depth of which is φdip∼2Tec/e, where Tec is the cold‐electron temperature. Interestingly, however, the positive potential difference and the negative potential dip are created independently.

The electric potential distribution profile in a naturally charged fluidized bed and its effects

Abstract: The electric potential profile on fluidized particles in acrylic and iron columns was measured with a spherical probe. The order of magnitude of the measurements is reasonable. The potential is strongly affected by the column material, the particle size, the type of particles, the gas velocity and humidity, and probably the diameter of the column. The dependence of the specific charge of the particles on the operating parameters is not clear. The calculated potential distributions show a maximum radial electric intensity near the column wall, with the resulting coalescence of particles leading to dead space and channeling.

Charge transport and trapping in silicon nitride-silicon dioxide dielectric double layers

Abstract: Time, electric field, and temperature dependence of the flat‐band voltage shift in polysilicon‐silicon nitride‐(thick) silicon dioxide‐silicon capacitors subjected to high field stress has been studied in this paper. A ‘‘turn around’’ effect in the behavior of the flat‐band voltage shift versus time is observed, both in the accumulation and in the strong inversion mode, in the full range of temperatures investigated (77 K≤T≤453 K). Early time charge trapping seems to be dominated by transport of carriers, holes or electrons injected at the gate electrode, in the nitride layer. A Poole–Frenkel‐active trap for holes is determined to be located at 1.0 eV above the nitride valence‐band edge and a Poole‐Frenkel‐active trap for electrons 1.3 eV below the nitride conduction‐band edge. The dark contact current‐contact field characteristics at the silicon‐silicon dioxide interface are obtained at room temperature for both gate bias conditions. The contact current for positive gate voltage J+ox appears to be domina...

Self-consistent calculation of the electron distribution at a jellium surface in a strong static electric field.

Abstract: The Hohenberg-Kohn-Sham formalism in local-density approximation is used to calculate self-consistently the effective potential and electron density profile at the surface of a jellium slab in a strong static electric field. In the wide range of induced surface-charge densities accessible to experiments in electrolytic cells, the shape of the calculated electron density profiles is characterized by suitable moments, and the induced charge density by its center of mass and by its width, which are related to static and to optical response properties, respectively. Comparison with previous work reveals the importance of self-consistency.

The Role of Unneutralized Surface Ions in Negative Potential Arcing

Abstract: The observed arcing on negatively biased solar arrays exposed to plasma environments is shown to be due to an effective charge layer on the interconnect formed by ion collection from the plasma. Time scales to form this layer are shown to be in agreement with experimental observations. A quantitative theory is presented which predicts arcing threshold dependence on plasma density and external potentials. After breakdown, the discharge process is modeled as space charge limited transport to nearby coverslips. Peak currents and decay times predicted by this model are compared with experimental observations.

Computed response of the space charge layer created by corona at ground level to external electric field variations beneath a thundercloud

Abstract: The present numerical simulation deals with ion creation by corona at ground level and their evolution between the ground and the thundercloud. The study starts from a previous model in which the external electric field was constant in time. As an extension, the new model includes several types of variation of the external electric field responsible for ion creation. The following phenomena are taken into account: (1) ion creation of both polarities (bipolar medium), (2) capture of small ions by neutral aerosol particles as well as by other ions of opposite polarity, and (3) influence of turbulent diffusion. The model provides the transient response of the space charge to two types of variation of the electric field created by a thundercloud: the rapid variation due to a lightning stroke and the slow recovery which occurs during regeneration. Time and space evolution of the various parameters are deduced from the computation: small and large ion concentrations, space charge density, and electric field. The different results reveal the tremendous influence of the space charge on the electric field variation at ground level, especially after a lightning stroke. Pulses of corona current higher than 20 nA m−2 following 20 kV m−1 field steps can create such a high ion concentration that the surface electric field can be rapidly reduced to a value close to the corona threshold regardless of the intensity aloft. Electric field profiles plotted after a lightning stroke often show opposite polarities of the electric field at ground level and aloft.

Magnetic generalization of the Kerr–Newman metric

Abstract: The exact expression of the magnetized Kerr–Newman metric is presented The obtained solution possesses five continuous arbitrary parameters; mass, angular momentum, electric charge, and electric and magnetic field parameters

Experimental Evidence of Charge Separation (Double Layer) in Laser-Produced Plasmas

Abstract: Simultaneous measurements of the plasma target potential and plasma charged particle currents have been made for Nd laser irradiances between 4 × 1012 and 1015 W/cm2. The results appear to give the first direct indication of double layers in laser-produced plasmas.

Interaction potential between a helium atom and metal surfaces.

Abstract: By employing an S-matrix theory for evanescent waves, the repulsive potential between a helium atom and corrugated metal surfaces has been calculated. P-wave interactions and intra-atomic correlation effects were found to be very important. The corrugation part of the interaction potential is much weaker than predicted by the effective-medium theory. Application to Cu, Ni, and Ag (110) surfaces gives good agreement with experiment without any adjustable parameters.