External Dc Electric Field Research Articles

Influence of DC and AC external electric field on the propagation of “plasma bullets” along DBD helium plasma jet

Plasma jet generated by sinusoidal DBD in a tube blown with He is not uniform along its length because of existence of so called “plasma bullets” (ionization waves) travelling in jet each half-cycle. The bullet velocity and the visual shape of plasma jet will change, if to vary the ambient conditions for plasma jet. This work is devoted to the detailed experimental study on influence of the external DC and AC electric field with different amplitude and polarity on the bullet propagation in plasma jet. It has been established that one can change appreciably the plasma bullet velocity and even wholly suppress the bullets in the plasma jet.

Crystallization under an External Electric Field: A Case Study of Glucose Isomerase

Electric fields have been employed to promote macromolecular crystallization for several decades. Although crystals grown in electric fields seem to present higher diffraction quality, these methods are not widespread. For most configurations, electrodes are in direct contact with the protein solution. Here, we propose a configuration that can be easily extended to standard crystallization methods for which the electrodes are not in direct contact with the protein solution. Furthermore, the proposed electrode configuration supplies an external DC electric field. Glucose Isomerase from Streptomyces rubiginosus crystals were grown at room temperature using the microbatch method in the presence of 1, 2, 4, and 6 kV. Several crystallization trials were carried out for reproducibility and statistical analysis purposes. The comparison with crystals grown in the absence of electric fields showed that crystallization in the presence of electric fields increases the size of crystals, while decreasing the number of nucleations. X-ray diffraction analysis of the crystals showed that those grown in the presence of electric fields are of higher crystal quality.

Quadratic electro-optic Kerr effect in doped graphene

We theoretically investigate one of the third-order nonlinear optical (NLO) effects, namely, the quadratic electro-optic Kerr effect (EOKE), in doped graphene. To avoid the screening of an in-plane external dc electric field by the graphene’s electrons, we propose to use ‘low-amplitude’ ( cm−1) terahertz radiation pulses focused onto the graphene sample collinearly with a normally incident optical beam of frequency ω. Using the Dirac cone approximation for the π-electron energy bands of graphene, we calculate the real part of the effective third-order NLO susceptibility , describing the EOKE in doped graphene under the above conditions. The results obtained show that a large electro-optic modulation of the graphene’s refractive index n (up to ) can be achieved by proper tuning the Fermi level of charge carriers in the graphene sample via electrostatic gating. Furthemore, a change of sign of the electro-optic Kerr coefficient of doped graphene can occur in the spectral range below the photon energy threshold value of , corresponding to the onset of the fundamental (single-photon) interband absorption in the graphene. These theoretical findings open up new opportunities for practical exploitation of the EOKE in graphene-based NLO devices.

Study of Lau fringes generated by a photorefractive volume grating

In this work the Lau fringes generated by using a combination of an amplitude grating and a photorefractive volume phase grating is theoretically and experimentally analyzed. A model based on the path integral formalism to calculate the patterns intensity is employed. We show that the Lau pattern behavior is governed by the output pupil diameter of the imaging recording system, the DC external electric field and the crystal thickness. The introduction of a phase modulation that gathers the previously mentioned parameters allows determining the condition to optimize the fringe visibility. In this case, the visibility maintains a sinusoidal dependence as it happened with planar grating experiments. The experimental results confirm the theoretical model proposed.

Effect of an electric field on friction of silicone rubber against steel in the motor base oil's environment

The paper presents the experimental results of research on the effect of an external DC electric field on the coefficient of friction of silicone rubber (elastomer) during its rubbing against a steel surface in the „pin–on–disc” experimental set-up. In the tests there were used silicone rubber samples, the pure PAG and PAO synthetic base oils and their blends with an antiwear (ZDDP) additive. The coefficient of friction μ was determined under conditions with and without an external DC electric field. A DC electric field was generated between a silicone rubber sample and a rotating steel disc (a friction pair). A sample holder was electrically isolated from other metal parts of a tribometer and was connected to one of the poles of a DC power supply, while the other pole was connected by means of the carbon brushes to a rotating steel disc. The experimental results show that the external DC electric field established between the rotating steel disc and a silicone rubber sample causes the coefficient of friction to decrease. It was also found that the coefficient of friction μ depends on the steel disc's angular velocity n, the contact pressure p, and the type of base oil and its blends with the additive used.

Effect of a DC external electric field on the properties of a nonuniform microwave discharge in hydrogen at reduced pressures

The effect of a dc external electrical field on the properties of a highly nonuniform electrode microwave discharge in hydrogen at a pressure of 1 Torr was studied using optical emission spectroscopy and selfconsistent two-dimensional simulations. It is shown that the negative voltage applied to the antenna electrode with respect to the grounded chamber increases the discharge radiation intensity, while the positive voltage does not affect the discharge properties. The simulation results agree well with the experimental data.

F-centers mechanism of long-term relaxation in lead zirconate-titanate based piezoelectric ceramics. 2. After-field relaxation

The paper presents results of experimental study of the dielectric constant relaxation during aging process in Pb(Zr,Ti)O3based solid solutions (PZT) after action of external DC electric field. The said process is a long-term one and is described by the logarithmic function of time. Reversible and nonreversible relaxation process takes place depending on the field intensity. The relaxation rate depends on the field strength also, and the said dependence has nonlinear and nonmonotonic form, if external field leads to domain disordering. The oxygen vacancies-based model for description of the long-term relaxation processes is suggested. The model takes into account the oxygen vacancies on the sample's surface ends, their conversion into [Formula: see text]- and [Formula: see text]-centers under external effects and subsequent relaxation of these centers into the simple oxygen vacancies after the action termination. [Formula: see text]-centers formation leads to the violation of the original sample's electroneutrality, and generate intrinsic DC electric field into the sample. Relaxation of [Formula: see text]-centers is accompanied by the reduction of the electric field, induced by them, and relaxation of the dielectric constant, as consequent effect.

Detecting depinning of polar nanoregions under dc external electric field in canonical relaxor ferroelectric Pb(Mg1/3Ta2/3)O3 via acoustic emission

Canonical relaxor ferroelectric Pb(Mg1/3Ta2/3)O3 single crystals were studied via acoustic emission in temperature range of 180–250 K covering their dielectric constant temperature maximum at Tm ≈ 202 K, and under dc external electric fields up to 1.2 kV cm−1. The dependence of Tm on dc external electric field exhibits a nonlinear behavior, characteristic of relaxors: it initially decreases, attains a sharp minimum at the threshold field of 0.25 kV cm−1 and then starts to increase, as the field enhances. The count rate of the accompanying acoustic emission exhibits two maxima: at 0.1 and 0.6 kV cm−1. The latter obviously corresponds to the end critical point, also characteristic of relaxors, while the former is attributed to a polar nanoregions depinning field at which the polar nanoregions start to be switched off from the intrinsic random electric fields to the dc external electric field. These data are discussed from the viewpoint of competition between random electric fields and an external electric field when affecting the polar nanoregions.

Generation of terahertz radiation in the interaction of coherent electromagnetic wave with a resonant medium in a constant external electric field

The paper shows that it is sufficient to place a resonance medium in an external dc electric field for the generation of low-frequency radiation at the resonant interaction of the medium and a coherent wave with carrier frequency of the optical range. Under certain conditions the carrier frequency of the generated radiation equals the Rabi frequency of the resonant interaction.

Behavior of the charge accumulation at the pressboard/oil interface under DC external electric field stress [Oct 15 2537-2542

Provides corrections to the above titled paper (ibid., vol. 22, no. 5, pp. 2537-2542, Oct. 2015).

A Two-Dimensional Extremely Short Optical Pulse in a System of Carbon Nanotubes in a Direct Current Electric Field

The effect of an external dc electric field on the two-dimensional extremely short optical pulse propagating in a zigzag carbon nanotube array was investigated. The electromagnetic field evolution in the investigated nanotube system is described by the Maxwell equations. Using numerical simulation, the interaction between the pulse electromagnetic field and the external electric field applied to the carbon nanotube array is analyzed.

Vplyv sta¬tychnoho elektrychnoho polya na histerezys svitloindukovanoho perekhodu Frederiksa v nematychniy komirtsi

The influence of an external dc electric field on the hysteresis of the light-induced Fr´eedericksz transition in a nematic liquid crystal cell in the field of a light beam with a finite diameter has been studied. The external electric field orientations perpendicular to the cell surface and along it, in the direction of the incident light polarization, are considered. The dependences of the Fr´eedericksz transition thresholds for the increasing and decreasing intensities of the incident light on the electric field strength and the transversal light beam size are obtained numerically. The values of transversal light beam size and electric field strength, for which the Fr´eedericksz transition has a hysteretic character, are found. The hysteresis loop width is shown to increase if the dc electric field perpendicular to the cell surface grows. At the same time, the hysteresis loop width decreases, if the electric field is oriented along the cell surface.

Electronic structure and optical properties of triangular GaAs/AlGaAs quantum dots: Exciton and impurity states

Electronic structure and optical properties in equilateral triangular GaAs/Al0.3Ga0.7As quantum dots are studied extensively. The effects of donor and acceptor impurity atoms positioned in the orthocenter of the triangle, as well as of the external DC electric field are taken into account. Binding energies of the impurity, exciton energies, interband photoluminescence peak positions as well as linear and non-linear optical properties in THz range caused by transitions between excitonic states are calculated and discussed.

Melt-crystallizations of poly (l-lactic acid) under external DC electric fields

The melt-crystallization behaviors of poly (l-lactic acid) (PLLA) in the presence of the external DC electric fields are reported. The real-time monitoring of the melt-crystallizations were provided with polarizing optical microscope at the isothermal crystallization temperatures Tc = 120 – 150 °C under the voltages VDC = 0–200 V. The crystal nucleation took place selectively at the edge of the anodes, and the highly oriented crystals grew in the direction perpendicular to the anode. The nucleation rate in the presence of the fields was much faster than that on the spherulite growth in the absence of the fields. The nucleation rate was also faster as the applied voltages were higher. On the other hand, the crystal growth rate was almost independent of the magnitude of the applied voltage value. The present experimental results indicated that the applications of the electric fields were helpful for accelerating the crystal nucleation rate of the PLLA.

Space-and-time current spectroscopy of a β-Ga₂O₃ crystal.

We report the excitation of the non-steady-state photoelectro-motive force in a monoclinic gallium oxide crystal. The crystal grown in an oxygen atmosphere is insulating and highly transparent for a visible light, nevertheless, the formation of dynamic space-charge gratings and observation of the photo-EMF signal is achieved under the laser illumination with wavelength λ = 532 nm. The induced ac current is studied for the cases of zero and non-zero external electric fields, which imply the non-resonant and resonant mechanisms of space-charge recording. The dependencies of the signal amplitude versus the frequency of phase modulation, light intensity, spatial frequency, light polarization and value of the external dc electric field are measured. The material demonstrates the anisotropy along the [100] and [010] directions, namely, there is a weak difference of the transport parameters and a pronounced polarization dependence of the signal. The photoconductivity and diffusion length of electrons are estimated for the chosen light wavelength.

Electric field dependences of Curie and Néel phase transition temperatures in magnetoelectric relaxor multiferroic Pb(Fe0.5 Ta0.5 )O3 crystals seen via acoustic emission

Pb(Fe0.5Ta0.5)O3 magnetic and ferroelectric relaxor multiferroic crystals have been studied under both temperature and dc external electric field conditions by means of acoustic emission technique. All the characteristic relaxor points as Burns Td ≈ 610 K and intermediate T* ≈ 500 K temperatures, as well as both Curie ferroelectric cubic-tetragonal Tc1 ≈ 259 K and tetragonal–monoclinic Tc2 ≈ 201 K structural and Neel antiferromagnetic–paramagnetic TN ≈ 187 K phase transitions have been successfully detected. It is shown that, when an external dc electric field is applied, both Tc1 and Tc2 exhibit a nonlinear or V-shape behavior and attain the sharp minima at threshold temperatures Tth1 ≈ 247 K and Tth2 ≈ 200 K with the threshold field Eth ≈ 0.1 kV cm−1, as the field enhances, while their acoustic emission count rate monotonically increases. It is shown, too, that the TN behaves linearly in dependence on dc electric field with a negative slope of about −20 K cm kV−1, while its acoustic emission count rate monotonically decreases. All these data are discussed from a viewpoint of presence of polar nanoregions and magnetoelectric coupling effect in Pb(Fe0.5Ta0.5)O3 crystals.

Nonequilibrium Dynamical Mean-Field Theory for the Charge-Density-Wave Phase of the Falicov-Kimball Model

Nonequilibrium dynamical mean-field theory (DMFT) is developed for the case of the charge-density-wave ordered phase. We consider the spinless Falicov-Kimball model which can be solved exactly. This strongly correlated system is then placed in an uniform external dc electric field. We present a complete derivation for nonequilibrium dynamical mean-field theory Green’s functions defined on the Keldysh-Schwinger time contour. We also discuss numerical issues involved in solving the coupled equations.

Plasmon-Induced Optical Conductivity of Graphene Driven by an Electric Field

Abstract We theoretically investigate the optoelectronic properties of graphene driven by an external DC electric field caused via in-plane source-drain voltage. It is found that the Drude part dominates the optical conductivity in the low-frequency region, whereas the plasmon effect can give rise to a relatively weak but observable the optical conductivity in the high-frequency region. Both the Drude and plasmon-induced parts of optical conductivity can be observed in the terahertz (THz) bandwidth. Drude part decreases monotonously with increasing of the photon frequency, the plasmon-induced part exhibits a peak at about ω−1 THz due to resonant plasmon-photon interaction in graphene. Moreover, we examined the dependence of plasmon-induced optical conductivity on the driving electric field and electron density and find that it depends sensitively on these parameters. It is indicated that the optical conductivity resulted from Drude and plasmon-induced parts in graphene can be tuned efficiently not only by electric gating but also by source-drain voltage.

Behavior of the charge accumulation at the pressboard/oil interface under DC external electric field stress

Mineral oils are commonly used for cooling and electrical insulation purposes in electrical power transformers. The physicochemical process appearing at the Pressboard/Oil interface, leads to the formation of an Electrical Double Layer (EDL). Therefore the interface is polarized by the EDL, the charge of one sign is generated within the solid medium and the opposite charge remains in the liquid medium. The process of flow electrification is due to the convection of the diffuse layer inside the liquid. The test loop was recently optimized with the addition of an energized wrapped copper electrode in the sensor. This modification allows studying the effect of an external electric field on the charge production and the distribution of the EDL : in the liquid via the streaming current (global charge production) and in the pressboard via the capacitive current. This capacitive current allows quantifying the accumulated charge within the pressboard plate (local charge production). Therefore, the dynamics of the accumulated charge refer to two EDL affected in the same way by the DC electric field. This paper proposes to show the influence of an external DC electric field on the accumulated charge within the pressboard as well as on the streaming current.

Electric-field induced nonlinear optical materials based on a bipolar copper (I) complex embedded in polymer matrices

Second order nonlinear optical properties of Cu(dppb)(pz2Bph2), where dppb = 1,2-bis(diphenylphosphino)benzene and pz2Bph2 = diphenyl-bis(pyrazol-1-yl)borate were investigated. In particular, optical second harmonic was generated with different polymer films containing dc-electric field aligned chromophore molecules. It was shown that in such dc-electric field aligned polymer films, the enhancement of the second order output efficiency may be up to 3 times higher with as compared to the non-aligned poly(methylmethacrylate) (PMMA). After switching off the external dc-electric field the second order susceptibility decreases within 5–7 min by about 40 % with respect to the photoinduced ones. After that time, the second harmonic generation efficiency remains constant for much more than a few hours.