Showing papers on "Electric field published in 1989"
TL;DR: In this article, the authors show that trap creation in both the bulk of silicon dioxide films and at its interfaces with silicon and metallic contacting electrodes is dependent on the presence of hot electrons in the oxide.
Abstract: Trap creation in both the bulk of silicon dioxide films and at its interfaces with silicon and metallic contacting electrodes is shown to depend on the presence of hot electrons in the oxide. For thick oxides (≥100 A), little trap creation is observed in the near‐thermal transport regime at electric field magnitudes less than 1.5 MV/cm. At these low fields, electrons travel in a streaming fashion close to the bottom of the oxide conduction band at energies less than that of the dominant optical phonon mode at 0.153 eV. At higher electric fields, the rate of bulk trap creation is proportional to the average energy of the hot electrons, which move in a dispersive manner and can reach energies as large as 4 eV. For thin oxides (<100 A) where electrons can travel ballistically (i.e., without scattering), traps are not produced unless injected electrons acquire more than 2 eV of kinetic energy from the applied electric field, regardless of the magnitude of this field. All data on both thin and thick oxides are shown to give a threshold for trap creation of about 2.3 eV by the hot electrons in the oxide conduction band. Also, trap creation is shown to be suppressed by lowering the lattice temperature below ≊150 K. Our results are discussed in terms of a model involving hydrogen‐related‐species release from defect sites near the anode by the hot electrons and the subsequent motion of these molecules to regions near the cathode where they can interact with the lattice and form the trapping sites which are measured.
576 citations
TL;DR: A sharp transport barrier, accompanied by a bifurcated poloidal rotation and a radial electric field, is formed at the plasma edge by driving a radial current across the outer magnetic surfaces of a tokamak.
Abstract: A sharp transport barrier, accompanied by a bifurcated poloidal rotation and a radial electric field, is formed at the plasma edge by driving a radial current across the outer magnetic surfaces of a tokamak. A decrease in particle transport is observed for negative radial E fields. When the radial current is turned off, the E field and the rotation damp on a time scale comparable with the ion-ion collision time.
527 citations
TL;DR: In this paper, the authors used a differential mobility classifier with a condensation nuclei counter as a detector to measure the electric field strength of a single particle in a time-varying electric field.
435 citations
TL;DR: A new method is developed that takes advantage of the large Coulomb repulsion of the nuclei within molecules rapidly stripped of their electrons to yield geometrical images of individual molecules.
Abstract: Most of our knowledge of the structures of free molecules comes from indirect observations that focus on other properties (for example, energy or mass spectra) that depend on structure. Recently, a new method has been developed that instead yields geometrical images of individual molecules. This method takes advantage of the large Coulomb repulsion of the nuclei within molecules rapidly stripped of their electrons. The first experiments with this new technique have already revealed structural images of several important species, such as positively charged methane ions.
267 citations
TL;DR: In this article, a simulation method is developed to investigate structure formation in electrorheological suspensions, where the suspension is treated as polarizable, spherical particles in a nonconducting medium, with the spheres subject to electric polarization forces due to an applied electric field and to hydrodynamic resistance due to their motion through the continuous phase.
Abstract: A simulation method is developed to investigate structure formation in electrorheological suspensions. The suspension is treated as polarizable, spherical particles in a nonconducting medium, with the spheres subject to electric polarization forces due to an applied electric field and to hydrodynamic resistance due to their motion through the continuous phase. The fibrous structures obtained from these simulations are independent of electric field strength and continuous phase viscosity in agreement with experimental observation. We have also found that the details of the simulated structures are sensitive to the treatment of the short‐range forces preventing particle overlap. When this force is represented by a form that accurately approximates a hard‐sphere interaction, the simulated structures agree well with those obtained experimentally, both with respect to their appearance and the time scale for structure formation.
239 citations
TL;DR: In this paper, a homogeneously aligned nematic liquid crystal cell with a hole-patterned electrode and with an indium-tin oxide (ITO-) coated counter-electrode has been prepared.
Abstract: A homogeneously aligned nematic liquid crystal cell with a hole-patterned electrode and with an indium-tin oxide (ITO-) coated counter-electrode has been prepared. A non-uniform electric field can be produced by the asymmetrical electrode structure. The liquid crystal director can be reoriented by applying a voltage across the electrodes, and this produces an axially symmetrical profile of the refractive index. This liquid crystal cell is expected to have a lens effect and so its optical properties have been investigated. The profile of the output light intensity was measured by using a detecting system with an optical fibre. Some relationships between the lens properties, the diameter of the hole and the thickness of the liquid crystal layer have been examined. The liquid crystal cell becomes a convex (converging) lens with a relatively low voltage. A focal length of several millimetres can be obtained by applying voltages of 3-4 V. As the applied voltage increases, the focal length becomes long...
201 citations
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TL;DR: In this article, the acceleration electrode is formed so as to have a structure in which a low magnetic permeability material of a certain thickness is stacked on the high magnetic perceptiveness material at a plasma chamber side and openings of ion exit holes are formed in the portion of the low magnetic permutation material.
Abstract: A microwave ion source suitable for an apparatus which requires ions of an element of high reactivity such as oxygen, fluorine, etc., the microwave ion source being arranged to transmit microwaves between outer and inner conductors of a coaxial line. An ion extraction electrode is formed at least partly of a low magnetic permeability material while an acceleration electrode is formed of a high magnetic permeability material. The acceleration electrode is formed so as to have a structure in which a low magnetic permeability material of a certain thickness is stacked on the high magnetic permeability material at a plasma chamber side and openings of ion exit holes are formed in the portion of the low magnetic permeability material. A permanent magnet constituting a magnetic field generating means is provided to surround the microwave lead-in coaxial line. The direction of magnetization of the permanent magnet is made to coincide with the axial direction of the coaxial line. The end surface of the permanent magnet at the microwave lead-in side is coupled with the periphery of the high magnetic permeability material of the acceleration electrode through another high magnetic permeability material to form a magnetic path. The plasma chamber is formed of a dielectric insulator which transmits microwaves well. It is possible to realize an ion source in which ions can be extracted with a high electric field, and in which a high current ion beam can be extracted for a long time.
178 citations
TL;DR: In this article, a two-dimensional axisymmetric model is proposed for the calculation of the electromageetic fields in an inductively coupled, radiofrequency (r.f.) plasma.
Abstract: Based on the electromagnetic vector potential representation, a two-dimensional, axisymmetric model is proposed for the calculation of the electromageetic fields in an inductively coupled, radiofrequency (r.f.) plasma. A comparative analysis made between the flow, temperature, and electromagnetic fields obtained using this model and those given by our earlier one-dimensional electromagnetic fields model show relatively little difference between the temperature fields predicted by the two models. Significant differences are observed, however, between the corresponding flow and electromagnetic fields. The new model offers an effective means of accounting for variations in the coil geometry on the flow and temperature fields in the discharge and for achieving a better representation of the electromagnetic fields under higher frequency conditions (f>10 MHz).
172 citations
TL;DR: In this paper, the electric field is precisely controlled by a molecular beam epitaxy grown on a highly doped layer and the pinned position of the Fermi level at the surface is determined from a measurement of both n and p−doped samples.
Abstract: The Franz–Keldysh oscillations induced by the electric field in the depleted zone below the GaAs surface are studied by photoreflectance spectroscopy. The electric field is precisely controlled by a molecular beam epitaxy grown buried highly doped layer and the pinned position of the Fermi level at the surface. It is shown that the electric field value as derived from theory is in disagreement with the value derived from electrostatic calculations. Consequently a determination of the Fermi level pinning is only possible from a measurement of both n‐ and p‐doped samples.
161 citations
TL;DR: In this article, the principles of ICRF antenna and Faraday screen design which minimize sputtering are discussed, and a theoretical analysis of the effect of the parallel electric field on the power density of the antenna is presented.
Abstract: In general, Faraday screen elements in an ICRF antenna are not aligned precisely along the combined toroidal and poloidal magnetic fields. When plasma of density n > 20V/eg2 ~ 109cm−3 (V being the voltage across the gap and g the gap spacing) is present in the gap between the elements, the electron response to the parallel electric field shorts out the electric field over most of the gap, leaving a narrow sheath of positive space charge and an intense electric field. This intense electric field accelerates ions up to an appreciable fraction of the gap voltage (~1 kV), sufficient to cause physical sputtering of the screen material. Impurities so generated constitute the principal limitationon power density for ICRF antennas. Principles of ICRF antenna and Faraday screen design which minimize sputtering are discussed.
159 citations
TL;DR: The transmission line model of return-stroke radiation, proposed by Uman and McLain (1970) has been tested on rocket-triggered lightning as mentioned in this paper, which leads to an average apparent velocity (derived from the ratio of peak field to peak current) of (151±017) × 108 m/s for 28 strokes.
Abstract: The “transmission-line model” of return-stroke radiation, proposed by Uman and McLain (1970), has been tested on rocket-triggered lightning Simultaneous measurements are reported of electric radiation field, current at the channel base, and stroke-propagation velocity Agreement between model and measurements is generally good during the first few microseconds, although several anomalies are pointed out Truncation of the sharp initial peak in many of the field waveforms, motivated by the hypothesis that the return stroke begins a short distance above the ground, leads to an average apparent velocity (derived from the ratio of peak field to peak current) of (151±017) × 108 m/s for 28 strokes, in excellent agreement with the average, photographically measured two-dimensional velocity of (152±017) × 108 m/s for 18 of these same strokes Although the correlation between apparent and photographic velocities for these 18 strokes is poor, the uncertainty in the photographic velocity determinations could explain most of the scatter The best formula for estimating peak currents (ip) in subsequent return strokes from remotely measured, truncated peak electric fields (E′p) at range D appears to be ip = −39 × 10−2 DE′p − 27 × 103, where all variables are in MKS units and the electric field polarity of return strokes lowering negative charge is considered negative
TL;DR: In this article, the authors studied the hole mobility in molecularly doped polymers, its electric field dependence, and compared with various functions proposed in the literature, concluding that only the function exp(E)1/2 is consistent with the data.
Abstract: One of the most puzzling aspects of the hole mobility in molecularly doped polymers, its electric field dependence, is studied. New data over the widest electric field range yet reported have been obtained and are compared with various functions proposed in the literature. Comprehensive linear and nonlinear statistical analysis reveals that only the function exp(E)1/2 is consistent with the data. The theoretical implications of this result are discussed.
IBM1
TL;DR: The magnetic-field-induced bifurcation of quantum levels into surface states and bulk-like Landau States was observed in this paper, where a single-particle energy spectrum was calculated.
Abstract: We observe the magnetic-field-induced bifurcation of quantum levels into surface states and bulklike Landau States. The disruption of the electric field quantization by a magnetic field is most dramatic for electrons bound in two dimensions perpendicular to the magnetic field. The interplay between competing spatial and magnetic quantization mechanisms results in a pronounced and complex level splitting. The observed splitting of zero-dimensional energy levels depends critically on the size of the quantum dots, and can be explained with a calculated single-particle energy spectrum.
01 Feb 1989
TL;DR: In this paper, a large-volume germanium detector with a full-depletion capacitance of only approximately 1 pf has been fabricated and the effect of impurity space charge was utilized to obtain an appropriate electric field distribution in the detector so that carriers are collected on a small area electrode.
Abstract: A large-volume (150 cm/sup 3/) germanium detector with a full-depletion capacitance of only approximately=1 pf has been fabricated. The effect of impurity space charge was utilized to obtain an appropriate electric field distribution in the detector so that carriers are collected on a small-area electrode. Detectors based on this principle are capable of very-low-noise operation and have immediate applications in experiments for the direct detection of dark matter. Detector pulse shapes and carrier-trapping effects were also examined for possible applications involving higher energy radiations. >
TL;DR: In this paper, the L-mode to H-mode transition in the DIII-D tokamak is associated with the sudden reduction in anomalous, fluctuation-connected transport across the outer midplane of the plasma.
Abstract: The authors' data indicate that the L-mode to H-mode transition in the DIII-D tokamak is associated with the sudden reduction in anomalous, fluctuation-connected transport across the outer midplane of the plasma. In addition to the reduction in edge density and magnetic fluctuations observed at the transition, the edge radial electric field becomes more negative after the transition. They have determined the scaling of the H-mode power threshold with various plasma parameters; the roughly linear increase with plasma density and toroidal field are particularly significant. Control of the ELM frequency and duration by adjusting neutral beam input power has allowed us to produce H-mode plasmas with constant impurity levels and durations up to 5 s. Energy confinement time in ohmic H-mode plasmas and in deuterium H-mode plasmas with deuterium beam injection can exceed saturated ohmic confinement times by at least a factor of two. Energy confinement times above 0.3 s have been achieved in these beam-heated plasmas with plasma currents in the range of 2.0 to 2.5 MA. Local transport studies have shown that electron and ion thermal diffusivities and angular momentum diffusivity are comparable in magnitude and all decrease with increasing plasma current.
Journal Article•
TL;DR: In this paper, the authors considered a thin-film n-i-n diode with impenetrable barriers and showed that the current density in a thin diode can be an order of magnitude larger than in a bulk diode.
Abstract: Space-charge-limited current is considered in a thin-film n-i-n diode. It is assumed that impenetrable barriers limit the current flow to a film of thickness D. Because the electric field of injected electrons spreads out of the film, the level of injection is substantially higher than in the bulk case described by the classical Mott-Gurney law. As a consequence, the current density in a thin diode can be an order of magnitude larger than in a bulk diode of the same length. It is shown that, in the limit of small D, the total current is independent of D because the decreasing film thickness is exactly compensated by increasing injection. In this limit analytic expressions of the current-voltage characteristics are obtained for several model electrode configurations. The analytic results are confirmed by a numerical simulation of the diode within a drift-diffusion model assuming a field-independent mobility. The numerical results also describe a transition with decreasing D from the Mott-Gurney law to the new law governing space-charge-limited current in a film. >
TL;DR: In this article, a parametric model of the ion transport through the cathode sheath is presented showing that the position of the peaks in the ion energy distribution depends only on a discharge scaling parameter and the spatial variation of the electric field across the sheath region.
Abstract: The energy distribution of ions incident on the cathode (smaller electrode) in a capacitively coupled asymmetric rf discharge was measured for different process parameters. It was found that the ion energy distribution exhibits a characteristic series of peaks, which are explained by the high‐frequency modulation of the sheath potential combined with charge exchange in the cathode sheath. A parametric model of the ion transport through the sheath is presented showing that the position of the peaks in the ion energy distribution depends only on a discharge scaling parameter and the spatial variation of the electric field e(x) across the sheath region. Good agreement between theoretical and experimental ion energy distributions in an argon discharge is obtained for an electric field variation e(x)∼xν with ν in the range 0.55–0.7.
Patent•
14 Sep 1989
TL;DR: A plasma process and an apparatus therefor are described in this paper, where a number of substrates are disposed between a pair of electrodes, to which a high frequency electric power is applied in order to generate glow discharge and induce a plasma.
Abstract: A plasma process and an apparatus therefor are described A number of substrates are disposed between a pair of electrodes, to which a high frequency electric power is applied in order to generate glow discharge and induce a plasma The substrates in the plasma are applied with an alternating electric field By virtue of the alternating electric field, the substrates are subjected to sputtering action
TL;DR: A theoretical model of the H-mode in tokamaks is presented in this article, which is based on the bifurcation of the radial electric field at the plasma edge.
Abstract: The paper presents a theoretical model of the H-mode in tokamaks which is based on the bifurcation of the radial electric field at the plasma edge. The electric field is determined by the balance of the non-ambipolar fluxes of ions and electrons at the edge. It is found that bifurcations of the radial electric field, the particle flux and the convective energy loss occur when the edge gradient reaches a critical value. This is attributed to L-H or H-L transition. The critical conditions are examined and the role of neutral particles as well as the effect of impurities are incorporated in the model. Combining the confinement scaling laws for both the core plasma and the scrape-off layer plasma, the threshold power for the transition is derived. The temporal evolution associated with the transition is studied.
TL;DR: In this article, the Intercosmos-Bulgaria-1300 satellite in the nearequatorial ionosphere over an earthquake center (φ ∗ = 3.39° S and λ ∗= 177.43° E, M = 4.8) on 21 January 1982
TL;DR: On met en evidence des ecarts par rapport a la loi d'Einstein lorsque le desordre et le champ augmentent, que l'on attribue a un phenomene de diffusion anormal induit par le champ alors that the mobilite reste constante.
Abstract: Employing Monte Carlo techniques, the diffusion and drift of charge carriers within an array of hopping states subject to a Gaussian distribution of site energies of width \ensuremath{\sigma} has been studied as a function of \ensuremath{\sigma}/kT and electric field. With increasing disorder and field, significant deviations from Einstein's law are noted. They are shown to be the consequence of anomalous, field-assisted diffusion while the mobility remains constant. The effect can account for anomalous transit-time dispersion observed in polymeric photoconductors exhibiting time independent transport.
TL;DR: In this article, the authors studied the effect of DC charge accumulation on the surface of a solid insulating support (spacer) in compressed SF/sub 6/ gas using various cylindrical model spacers.
Abstract: Mechanism and effect of DC charge accumulation on the surface of a solid insulating support (spacer) have been studied in compressed SF/sub 6/ gas using various cylindrical model spacers. The distribution of surface charged is closely related to the normal component (gas side) E/sub n/ of electric field on the spacer surface. The ,maximum charge density can be estimated from the condition of E/sub n/=0. When voltage is applied in a polarity opposite to prestressed DC, surface charge increases the maximum field strength in the arrangement, resulting in the reduction of the insulating ability. It is possible to estimate the lowest flashover voltage due to surface charges only from numerical fields calculations. An anticharging spacer shaped along electric lines of force is proposed and studied. >
TL;DR: In this article, the relationship between the morphology of energetic particle substorm injections and the change in the magnetic field magnitude over the course of the event is examined using the statistical relationships between the magnetic fields during the growth phase and the changes in the field magnitude during substorms calculated by Lopez et al.
Abstract: The relationship between the morphology of energetic particle substorm injections and the change in the magnetic field magnitude over the course of the event is examined. Using the statistical relationships between the magnetic field during the growth phase and the change in the field magnitude during substorms calculated by Lopez et al. (1988), a limited number of dispersionless ion injections observed by AMPTE CCE are selected. It is argued that this limited set is representative of a large set of events and that the conclusions drawn from examining those events are valid for substorms in general in the inner magnetosphere. It is demonstrated that in an event when CCE directly observed the disruption of the current sheet, the particle and field data show that the region of particle acceleration was highly turbulent and was temporally, and perhaps spatially, limited and that the high fluxes of energetic particles are qualitatively associated with intense inductive electric fields.
TL;DR: In this article, the air conductivity and the vertical electric field were measured over thunderstorms from a high-altitude U-2 airplane during the summer of 1986, and the results indicated that the relative efficiency of a thunderstorm to supply current to the global electric circuit has an inverse relationship to the strength of the cloud electrical generator.
Abstract: During the summer of 1986, the air conductivity and the vertical electric field were measured over thunderstorms from a high-altitude U-2 airplane. The conductivity near 20 km was found to be relatively steady above storms with variations less than ±15%. In addition, the positive and negative conductivities were at all times approximately equal and displayed a very similar temporal/spatial behavior. While traversing thunderstorms, sustained upward directed electric fields were maintained along the flight path over distances of 20 to 40 km, and electric fields in excess of 5 kV/m were often observed while passing over very intense storm centers. Estimates of the storm generator current and the Wilson conduction current were obtained for 15 storm over-flights using the current densities derived from the conductivity and field measurements and integrated over area. Area-integrated Maxwell currents of 0.09 to 5.9 A were observed with an average of 2.2 A. The U-2 data show that this measure of storm current varies linearly with flash rate, which suggest that the average charge transfer per discharge is independent of storm development or activity. The Wilson conduction current, which contributes to the global circuit, varied between 0.09 and 3.7 A above storms with an average of 1.7 A. The conduction current was not found to be linearly related to the total flash rate but, instead, leveled off with increasing flash rate. This result may indicate that the relative efficiency of a thunderstorm to supply current to the global electric circuit has an inverse relationship to the strength of the cloud electrical generator.
TL;DR: The dependence of structural resonance behavior on focal point positioning for a spherical particle illuminated by a tightly focused (beam diameter less than sphere diameter), linearly polarized, Gaussian-profiled laser beam was investigated in this article.
Abstract: The spherical particle/arbitrary beam interaction theory developed in an earlier paper is used to investigate the dependence of structural resonance behavior on focal point positioning for a spherical particle illuminated by a tightly focused (beam diameter less than sphere diameter), linearly polarized, Gaussian‐profiled laser beam. Calculations of absorption efficiency and distributions of normalized source function (electric field magnitude) are presented as a function of focal point positioning for a particle with a complex relative index of refraction of n=1.33+5.0×10−6i and a size parameter of α≊29.5 at both nonresonance and resonance conditions. The results of the calculations indicate that structural resonances are not excited during the on‐center focal point positioning of such a tightly focused beam but structural resonances can be excited by proper on‐edge focal point positioning. Electric wave resonances were found to be excited by moving the focal point from on‐center towards the edge of the sphere parallel to the direction of the incident beam electric field polarization. Magnetic wave resonances were found to be excited by moving the focal point from on‐center towards the edge of the sphere perpendicular to the direction of the incident beam electric field polarization.
TL;DR: The evolution of the measured cluster size distribution exhibits significant departures from theory at large times due to the formation of long linear clusters which effectively partition space into isolated one-dimensional strips.
Abstract: Dilute suspensions of micron diameter dielectric spheres confined to two dimensions are induced to aggregate linearly by application of an electric field. The growth of the average cluster size agrees well with the Smoluchowski equation, but the evolution of the measured cluster size distribution exhibits significant departures from theory at large times due to the formation of long linear clusters which effectively partition space into isolated one-dimensional strips.
TL;DR: In this article, the nonlinear response of a two-state chemical transition to an oscillating electric field is examined and Fourier coefficients are calculated for the enzyme state probability in the ac field, exactly for infinite frequency, and in powers of the field for finite frequency.
Abstract: The nonlinear response of a two‐state chemical transition to an oscillating electric field is examined. A reaction for which this analysis is particularly relevant is a conformational transition of a membrane protein exposed to an ac electric field. Even a modest externally applied field leads to a very large local field within the membrane. This gives rise to nonlinear behavior. The applied ac field causes harmonics in the polarization and can cause a dc shift in the state occupancy, both of which can be observed and used to determine kinetic parameters. Fourier coefficients are calculated for the enzyme state probability in the ac field, exactly for infinite frequency, and in powers of the field for finite frequency. Kramers–Kronig relations are proved and response functions are given for the leading terms of the harmonics. The results are extended to the spherical symmetry relevant to suspensions of spherical cells, vesicles, or colloidal particles. If the protein catalyzes a reaction, free energy is t...
TL;DR: In this paper, an interpretation of current-time transients describing anodic oxide film growth on metals is presented, which can be linearized by using an integrated form of Cabrera and Mott's equation.
Abstract: An interpretation of current-time transients describing anodic oxide film growth on metals is presented. When the rate of oxide film growth is controlled by ion conduction under high electric field, the classical theory of Cabrera and Mott leads to shallow curvature in plots of log i vs. log t. Such data can be linearized by using an integrated form of Cabrera and Mott's equation. The predicted form of the current transient shows log i decaying linearly as (i-t)/sup -1/2/ from which film growth parameters may be calculated. The equations distinguish sensitively between Cabrera-Mott film growth kinetics and direct logarithmic film growth kinetics. The effects of the presence of an ohmic potential drop in the electrolyte are shown. The equations are tested in terms of anodic oxide film growth on iron and titanium.