Presence Of Large Electric Fields Research Articles

Water liquid-vapor interface subjected to various electric fields: A molecular dynamics study.

Investigation of the effects of E-fields on the liquid-vapor interface is essential for the study of floating water bridge and wetting phenomena. The present study employs the molecular dynamics method to investigate the effects of parallel and perpendicular E-fields on the water liquid-vapor interface. For this purpose, density distribution, number of hydrogen bonds, molecular orientation, and surface tension are examined to gain a better understanding of the interface structure. Results indicate enhancements in parallel E-field decrease the interface width and number of hydrogen bonds, while the opposite holds true in the case of perpendicular E-fields. Moreover, perpendicular fields disturb the water structure at the interface. Given that water molecules tend to be parallel to the interface plane, it is observed that perpendicular E-fields fail to realign water molecules in the field direction while the parallel ones easily do so. It is also shown that surface tension rises with increasing strength of parallel E-fields, while it reduces in the case of perpendicular E-fields. Enhancement of surface tension in the parallel field direction demonstrates how the floating water bridge forms between the beakers. Finally, it is found that application of external E-fields to the liquid-vapor interface does not lead to uniform changes in surface tension and that the liquid-vapor interfacial tension term in Young's equation should be calculated near the triple-line of the droplet. This is attributed to the multi-directional nature of the droplet surface, indicating that no constant value can be assigned to a droplet's surface tension in the presence of large electric fields.

Difference equation solutions for hopping transport of ions through membranes

Difference equations provide a more natural representation than do differential equations for the hopping conduction of charged particles in material media. The discreteness of a material medium on an atomistic scale can lead to large physical effects such as nonohmic currents in the presence of large electric fields. A steady-state expression for the current has been obtained by summing the coupled difference equations for transport of a single species in the limit of arbitrarily large values of the space charge density due to the mobile carriers, with a concentration gradient across the membrane included. The transient response has also been worked out, but only in the homogeneous field limit. It is concluded that the combination of high electric fields with the natural microscopic discreteness of the diffusion medium can result in readily observable nonlinear electric field effects which increase approximately exponentially with the separation distances of the discrete energy barriers

Modified electron-beam-induced deposition of metal nanostructure arrays using a parallel electron beam

A modified electron-beam-induced deposition method using a parallel beam of electrons is developed. The method relies on the buildup of surface potential on an insulating surface exposed to an electron beam. Presence of sharp edges on the insulating surface implies presence of large electric fields that lead to site-specific nucleation of metal vapor on those regions. Feature sizes as small as 20nm can be deposited without the need to use fine probes, and thus the limitation of probe size imposed on the resolution is overcome. The use of pure metal vapor also renders the process inherently clean.

Incoherent radar spectra in the auroral ionosphere in the presence of a large electric field: The effect of O+-O+ Coulomb collisions

Abstract We have used Monte Carlo simulations of O+ velocity distributions in the high latitude F- region to improve the calculation of incoherent radar spectra in auroral ionosphere. The Monte Carlo simulation includes ionneutral, O+-O collisions (resonant charge exchange and polarization interaction) as well as O+-O+ Coulomb self-collisions. At high altitudes, atomic oxygen O and atomic oxygen ion O+ dominate the composition of the auroral ionosphere and consequently, the influence of O+-O+ Coulomb collisions becomes significant. In this study we consider the effect of O+-O+ Coulomb collisions on the incoherent radar spectra in the presence of large electric field (100 mVm-1). As altitude increases (i.e. the ion-to-neutral density ratio increases) the role of O+-O+ Coulomb self-collisions becomes significant, therefore, the one-dimensional, 1-D, O+ ion velocity distribution function becomes more Maxwellian and the features of the radar spectrum corresponding to non-Maxwellian ion velocity distribution (e.g. baby bottle and triple hump shapes) evolve to Maxwellian ion velocity distribution (single and double hump shapes). Therefore, O+-O+ Coulomb self-collisions act to isotropize the 1-D O+ velocity distribution by transferring thermal energy from the perpendicular direction to the parallel direction, however the convection electric field acts to drive the O+ ions away from equilibrium and consequently, non-Maxwellian O+ ion velocity distributions appeared. Therefore, neglecting O+-O+ Coulomb self-collisions overestimates the effect of convection electric field.

Influence of temperature on the electromechanical and fatigue behavior of piezoelectric ceramics

This paper presents research results on the electro–thermomechanical behavior of piezoelectric ceramics for use in actuator applications with an emphasis on ferroelectric fatigue. The material being investigated is a lead zirconate titanate piezoelectric ceramic with the composition PbZr0.53Ti0.47O3 (PZT-5H). Results presented in this paper include an augmented constitutive model that accounts for the temperature-dependent piezoelectric properties. Using this model, nonlinear effects measured at one temperature can be extrapolated to other temperatures with good accuracy. Experimental studies into 180° and 90° polarization switching of PZT-5H indicate that the dielectric flux to dipole the material appears to be an adequate criterion for predicting this nonlinear switching behavior. Fatigue studies show that material degradation is strongly influenced by temperature and by the magnitude of the applied electric field. Above a critical temperature, PZT-5H no longer fatigues in the presence of large electric fields due to changes in the electromechanical properties such as the depolarization strain. Using a finite element model incorporating the proposed constitutive relations along with a domain switching criterion, this paper suggests that fatigue degradation is primarily caused by mechanical stresses in the material resulting from spatially variant electric fields causing preferential domain wall motion. The large stress mismatches induce mechanical damage in the form of cracks.

Cosmic radio noise absorption related to structures in auroral luminosity

Digitized all‐sky white light images of auroral optical emissions, recorded by a low‐light level TV system at Sanae (70.3°S, 2.4°W, L = 4.0), have been mapped onto the angular sensitivity functions of the inner four beams of a 16‐element imaging riometer. Cosmic radio waves of 5–10 m wavelengths appeared to be absorbed more strongly in directions through regions adjacent to discrete auroral arcs than through the arc regions themselves. These stronger absorptions may be due either to enhanced electron temperatures, caused by the Farley‐Buneman two‐stream instability in the presence of large electric fields around auroral arcs in the E region, or to D region absorption caused by energetic electrons precipitating along magnetic field lines passing through regions adjacent to auroral arcs. The two auroral events before local magnetic midnight reported in this paper started with high luminosity and small ionospheric absorption. The absorption increased as the event developed. Auroral luminosities and structures were changing in all four viewing directions during the event on May 10, 1992, with variations in absorptions following variations in luminosity after a delay of 30 s. The event on June 8, 1992, involved a pulsating arc structure. Changes in absorption appeared to be delayed relative to changes in luminosity that varied from 0 to 60 s in a particular viewing direction. The auroral event after local magnetic midnight on April 14, 1993, differed from the former two events in the appearance of pulsating auroral patches and in slower temporal variations, but, occasionally, changes in absorption of cosmic radio noise in the four beam directions were still delayed relative to changes in luminosity. The observed spatial and temporal differences in regions of optical emissions and ionospheric absorption should be of magnetospheric origin rather than ionospheric origin on account of the long delay times.

Field‐aligned Poynting Flux observations in the high‐latitude ionosphere

We have used data from Dynamics Explorer 2 to investigate the rate of conversion of electromagnetic energy into both thermal and bulk flow particle kinetic energy in the high‐latitude ionosphere. The flux tube integrated conversion rate E·J can be determined from spacecraft measurements of the electric and magnetic field vectors by deriving the field‐aligned Poynting flux, S , where is in the direction of the geomagnetic field. Determination of the Poynting flux from satellite observations is critically dependent upon the establishment of accurate values of the fields and is especially sensitive to errors in the baseline (unperturbed) geomagnetic field. We discuss our treatment of the data in some detail, particularly in regard to systematically correcting the measured magnetic field to account for attitude changes and model deficiencies. S∥ can be used to identify the relative strengths of the magnetosphere and thermospheric winds as energy drivers and we present observations demonstrating the dominance of each of these. Dominance of the magnetospheric driver is indicated by S∥ directed into the ionosphere. Electromagnetic energy is delivered to and dissipated within the region. Dominance of the neutral wind requires that the conductivity weighted neutral wind speed in the direction of the ion drift be larger than the ion drift, resulting in observations of an upward directed Poynting flux. Electromagnetic energy is generated within the ionospheric region in this case. We also present observations of a case where the neutral atmosphere motion may be reaching a state of sustained bulk flow velocity as evidenced by very small Poynting flux in the presence of large electric fields.

Effect of the charge-density-wave transition on the thermal expansion of 2H-TaSe2, NbSe3, and o-TaS3.

With the help of a tunneling capacitance dilatometer we have measured the thermal expansion near the Peierls temperature (${\mathit{T}}_{\mathit{C}}$) in three charge-density-wave materials. For the layered compound 2H-${\mathrm{TaSe}}_{2}$, the expansion was measured along the basal plane, while in the trichalcogenides ${\mathrm{NbSe}}_{3}$ and o-${\mathrm{TaS}}_{3}$ the expansion was measured along the molecular chains. For 2H-${\mathrm{TaSe}}_{2}$ the thermal-expansion coefficient showed a peak with a shape very similar to that reported for the specific heat. In ${\mathrm{NbSe}}_{3}$ the expansion coefficient showed a discontinuity at ${\mathit{T}}_{\mathit{C}}$, consistent with a mean-field interpretation of the phase transition. For o-${\mathrm{TaS}}_{3}$ the expansion coefficient was measured in the presence of large electric fields. The results suggest a mean-field jump in the expansion coefficient which is of opposite sign to that observed in ${\mathrm{NbSe}}_{3}$.

Atomic and molecular ion temperatures and ion temperature anisotropy in the auroral F region in the presence of large electric fields

The atomic O+ ion oxygen and molecular NO+ ion nitrogen temperatures and temperature anisotropy throughout a realistic auroral F region in the presence of large electric fields are studied. The O+ ion temperature is smaller than the NO+ ion temperature in the lower part of the F region, and this effect increases with the increasing of the neutral temperature as well as of the ion‐neutral drift velocity. The ion temperature anisotropy is defined as the ratio of the ion perpendicular temperature to the ion parallel temperature with respect to the magnetic field. For the O+ ions this ratio is maximum around 290 km in altitude for a constant ion‐neutral drift velocity throughout the F region. For similar conditions the NO+ ion temperature anisotropy is constant between 175 km and 250 km in altitude and decreases for higher altitudes. Application to mixed species non‐Maxwellian radar spectra analysis is discussed.

The three‐dimensional raman's distribution as a non‐Maxwellian model and the ionospheric ion outflows into the magnetosphere revisited

The three‐dimensional Raman's distribution as a model for fitting non‐Maxwellian distributions, and the consequences for the hydrodynamic mirror force due to coupling between pressure anisotropy and the inhomogeneous geomagnetic field are revisited. We demonstrate that the three‐dimensional Raman's model is unable to quantitatively predict the Post‐Rosenbluth or ion cyclotron instability threshold. The application of this model to deduce ion temperature anisotropy from only one radar spectra measurement is shown to be restricted to specific aspect angles and small electric field intensities. This model provides the line‐of‐sight temperature and then the thermodynamical temperature for aspect angle equal to 54.7°. The hydrodynamic upwelling force is shown to be greatly affected by the ion‐neutral interaction process. This additional force represents an important amount of the gravity in the presence of large electric fields. The upwelling force is overestimated to a great extent, when using the three‐dimensional Raman's model to fit non‐Maxwellian distribution functions observed in the auroral ionosphere.

High-field transport phenomenology: Hot-electron generation at semiconductor interfaces.

The transport of electrons in large, inhomogeneous electric fields is described using a phenomenological approach. The competing effects of acceleration and deceleration of the carriers due to the electric field and the scattering by phonons, respectively, are described by a drift-diffusion equation (Fokker-Planck equation) in energy space. In the Fokker-Planck equation, the scattering processes are treated in an averaged manner: First, inelastic scattering gives rise to an average friction force, which opposes the acceleration by the electric field. Second, the random character of the scattering introduces an energy dispersion. The combination of electric field and friction force determines the drift of the particle flow in energy space, whereas the energy-dispersion term determines its diffusion. The formalism is applied to the problem of hot-electron and minority-carrier generation in the depletion region of charged semiconductor interfaces. The friction force and the energy dispersion are determined for the case of polar-optic-phonon scattering. Acoustic-phonon scattering and pair creation are taken into account. We find that the isotropic character of the polar-optic-phonon scattering at very low carrier energies greatly enhances the friction force experienced by the electrons. The resulting peak in the friction force found at low energies is suppressed in the presence of large electric fields. As a result, we find that the yields for hot-electron and minority-carrier generation depend critically on the field strength via the donor concentration in the semiconductor. These results have implications for the breakdown behavior of a varistor.

Generalization of Fröhlich's thermodynamic model of the living state phase transition

Based on some experimental evidence for the existence of metastable ferroelectric phases in living substances Fröhlich proposed a simple thermodynamic description of the living state. The free energy of a cell is written as a polynomial in the total electric polarization and the macroscopic deformation. The two variables are coupled which allows for piezoelectric effects. Haken argued that the transition to the living state is a field-induced phase transition and Fröhlich included the presence of large electric fields as a prerequisite for the biological coherence. Therefore, the thermodynamic formulation requires an additional term representing interactions with an external electric field. We analyze a generalized model free energy and arrive at results which confirm earlier predictions. Above a threshold field a ferroelectric phase can be established which remains stable even after the field has been removed. In conclusion, a possible further generalization of the model to embrace time dependence and spatial inhomogeneities is sketched. It appears that a link with Prigogine's theory of dissipative structure can be traced.

Scattering of Electrons in Crystals in the Presence of Large Electric Fields

By the calculation of transitions between states appropriate to electrons moving in a large uniform electric field superimposed on a periodic crystal field, it is shown the probabilities of scattering by lattice vibrations or imperfections are independent of the uniform field and are given by the usual expressions derived for zero field. This justifies the procedure of treating acceleration by the field and scattering as independent processes.