External Dc Electric Field Research Articles

Linear Impurity Structures in the Ferroelectric Ba5Ti2O7Cl4

In the new ferroelectric Ba5Ti2O7Cl4 one can observe in the microscope under reflected light black lines that are not domain lines. These lines appear in regular crystallographic directions on a given crystallographic plane. It is shown that such lines are formed by atomic impurities that are not close to each other on atomic scale, and hence do not form a separate phase. The impurities occur close to each other on account of strain energy associated with them. These ordered impurities scatter light and give an optical illusion that the lines form a separate phase in the crystal matrix. When an external dc electric field was applied to the crystal the point defects got scattered in the crystal structure. The possible orientations of domain lines and these linear structures are exactly the same. The two can, however, be distinguished by chemical etching.

Collisional activation of ions in RF ion traps and ion guides: The effective ion temperature treatment

Ion transfer and storage using inhomogeneous radio frequency (RF) electric fields in combination with gas-assisted ion cooling and focusing constitutes one of the basic techniques in mass spectrometry today. The RF motion of ions in the bath gas environment involves a large number of ion-neutral collisions that leads to the internal activation of ions and their effective "heating" (when a thermal distribution of internal energies results). The degree of ion activation required in various applications may range from a minimum level (e.g., slightly raising the average internal energy) to an intense level resulting in ion fragmentation. Several research groups proposed using the effective temperature as a measure of ion activation under conditions of multiple ion-neutral collisions. Here we present approximate relationships for the effective ion temperature relevant to typical operation modes of RF multipole devices. We show that RF ion activation results in near-thermal energies for ions occupying an equilibrium position at the center of an RF trap, whereas increased ion activation can be produced by shifting ions off-center, e.g., by means of an external DC electric field. The ion dissociation in the linear quadrupole ion trap using the dipolar DC ion activation has been observed experimentally and interpreted in terms of the effective ion temperature.

Transient electroosmotic flow induced by DC or AC electric fields in a curved microtube.

This study investigates transient electroosmotic flow in a rectangular curved microtube in which the fluid is driven by the application of an external DC or AC electric field. The resultant flow-field evolutions within the microtube are simulated using the backwards-Euler time-stepping numerical method to clarify the relationship between the changes in the axial-flow velocity and the intensity of the applied electric field. When the electric field is initially applied or varies, the fluid within the double layer responds virtually immediately, and the axial velocity within the double layer tends to follow the varying intensity of the applied electric field. The greatest net charge density exists at the corners of the microtube as a result of the overlapping electrical double layers of the two walls. It results in local maximum or minimum axial velocities in the corners during increasing or decreasing applied electric field intensity in either the positive or negative direction. As the fluid within the double layer starts to move, the bulk fluid is gradually dragged into motion through the diffusion of momentum from the double layer. A finite time is required for the full momentum of the double layer to diffuse to the bulk fluid; hence, a certain phase shift between the applied electric field and the flow response is inevitable. The patterns of the axial velocity contours during the transient evolution are investigated in this study. It is found that these patterns are determined by the efficiency of momentum diffusion from the double layer to the central region of the microtube.

Electric current of hot electrons in semiconductor thin films

A theory of nonlinear electric conductivity in a semiconductor film is offered. This nonlinearity is caused by heating of charge carriers in an external dc electric field. For the first time nonequilibrium charge carriers appearing due to the presence of the same heating electric field are taken into account. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Acoustoelectric effects in Sn2P2S6-type ferroelectric semiconductors

Results of ultrasonic and acoustoelectric measurements of Sn2P2(S,Se)6 and CuInP2S6 ferroelectric semiconductor single crystals are presented. We have studied acoustoelectric effects produced by longitudinal ultrasonic waves in single crystals in the vicinity of a phase transition. The experiments revealed in the longitudinal bulk acoustoelectric (AE) effect an anomalously large contribution, invariant upon reversal of the direction of ultrasound propagation, which coexists with ordinary (odd wave vector) effect. It was shown that this even wave vector effect increases near the phase transition and its sign can be changed by an external dc electric field along the ferroelectric axis. In CuInP2S6 crystals the even AE effect dominates. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Biosorption of heavy metals in an aqueous solution by aerobic biofilm subjected to an external dc electric field

Electro biosorption is a potential technology for reclamation of wastewater laden with heavy metal ions present in low concentrations. In this study, multi‐species micro‐organisms in aerobic biofilms demonstrated a great capacity to adsorb, and a direct current (DC) electric field with low intensity was able to promote the directional movements of heavy metals in wastewater and strengthen the interactions between heavy metals and microbes in biofilms. A two‐dimensional model was established to describe wastewater flow and the transfer and adsorption of heavy metal ions by biofilms in a weak DC electric field. The simulation results for low concentrations of Cu2 + or Cr3 + ions in outlet water were tested by an electro biosorption experiment, and the influence of the electric field intensity, the inlet concentration of heavy metal ions and the wastewater flow velocity on the equilibrium adsorption amount are discussed in detail. The equilibrium adsorption amount increased rapidly in the initial stage, and became slow afterwards, along with the increase in the electro field intensity. There was a linear relationship between the equilibrium adsorption amount and the inlet concentration of heavy metal ions. Wastewater flow velocity had an obvious effect on the equilibrium adsorption amount; the equilibrium adsorption amount decreased rapidly at first and the decrease subsequently became slow along with an increase in wastewater flow velocity.

Dc electric-field dependence of the dielectric constant in polar dielectrics: Multipolarization mechanism model

The dc electric-field dependence of the relative dielectric constant ${\ensuremath{\varepsilon}}_{r}(E)$ in polar dielectrics is studied. The Landau-Ginzburg-Devonshire (LGD) theory and its approximate treatments in dealing with ${\ensuremath{\varepsilon}}_{r}(E)$ are reviewed. It is found that the LGD theory works well in the case of a single polarization mechanism existing in the dielectrics, and the Johnson relation ${\ensuremath{\varepsilon}}_{r}(E)={\ensuremath{\varepsilon}}_{r}(0)/{1+\ensuremath{\lambda}[{\ensuremath{\varepsilon}}_{0}{\ensuremath{\varepsilon}}_{r}(0){]}^{3}{E}^{2}{}}^{1/3}$ is a reasonable approximate expression describing ${\ensuremath{\varepsilon}}_{r}(E).$ Many polar dielectrics, however, exhibit more than one polarization mechanism contributing to the total dielectric constant. The dielectric response of such polar dielectrics under an external dc electric field cannot be purely described by LGD theory. In this work, we introduce a ``reorientational polarization'' to describe the ``extrinsic'' contribution to the dielectric constant, such as might arise from polar clusters, domain-wall motions, fluctuation of microcluster boundaries, defects, etc. A ``multipolarization-mechanism'' model is proposed, and a combined equation ${\ensuremath{\varepsilon}}_{r}(E)={\ensuremath{\varepsilon}}_{r}(0)/{1+\ensuremath{\lambda}[{\ensuremath{\varepsilon}}_{0}{\ensuremath{\varepsilon}}_{r}(0){]}^{3}{E}^{2}{}}^{1/3}+\ensuremath{\Sigma}{(P}_{0}x/{\ensuremath{\varepsilon}}_{0})[\mathrm{cosh}(\mathrm{Ex}){]}^{\ensuremath{-}2}$ is adopted to describe the total ${\ensuremath{\varepsilon}}_{r}(E)$ response of a polar dielectric, where the first term is Johnson's relation which represents the ``intrinsic'' polarization, and the latter represents the ``extrinsic'' polarization. Agreement between the fitting of this equation to the experimental data is obtained for paraelectrics ${\mathrm{KTaO}}_{3}$ and ${\mathrm{B}\mathrm{i}:\mathrm{S}\mathrm{r}\mathrm{T}\mathrm{i}\mathrm{O}}_{3}.$

Effects of an external electric field applied during the solution heat treatment of the Al–Mg–Si–Cu alloy AA6111

Abstract The application of an external dc electric field during the solution heat treatment (SHT) of AA6111 Al alloy increased the as-quenched resistivity ρ and hardness Hv. The increases represented reductions in SHT of 10–20 K required for a constant ρ or Hv. Analysis of the results gave that the field reduced both the enthalpy and entropy of solution. The resulting reduction in Gibbs free energy gave increases of 0.03–0.04 at.% in solubility of Mg2Si (or Al–Mg–Si–(Cu)-vacancy complexes) at 400–600°C, amounting to a factor of 33 % increase in solubility at 400°C and 6% at 600°C.

Effective dielectric response of nonlinear composites with external ac and dc electric field

The perturbation method is developed to investigate the effective nonlinear dielectric response of Kerr composites when the external ac and dc electric field is applied. Under the external ac and dc electric field Eapp=Ea(1+sin ωt), the effective coupling nonlinear response can be induced by the cubic nonlinearity of Kerr nonlinear materials at the zero frequency, the finite basic frequency ω, the second and the third harmonics, 2ω and 3ω, and so on. As an example, we have investigated the cylindrical inclusions randomly embedded in a host and derived the formulas of the effective nonlinear dielectric response at harmonics in dilute limit. For a higher concentration of inclusions, we have proposed a nonlinear effective-medium approximation by introducing the general effective nonlinear response. With the relationships between the effective nonlinear response at harmonics and the general effective nonlinear response, we have derived a set of formulas of the effective nonlinear dielectric responses at harmonics for a larger volume fraction.

Polysilicon Encapsulation Gettering with Electric-Field-Enhanced Isothermal Annealing for Copper Impurities in Bulk Silicon

A metal gettering strategy for copper in silicon, combining polysilicon encapsulation, isothermal annealing, and an external dc electric field is proposed. Experimental results have shown faster gettering of copper at the polysilicon layer to a higher concentration level above the copper detection limits of total reflection X-ray florescence spectroscopy. The improvement in the observed gettering efficiency is attributed to the directional drift-diffusion of copper interstitials to the effective polysilicon gettering sites, under the influence of the applied potential gradient and the thermally induced gettering concentration gradient, respectively, providing a simple and effective method for minimizing and monitoring of Cu content in bulk silicon wafers. (C) 2004 The Electrochemical Society.

LC Alignment Controlled by Photoordering and Photorefraction in a Command Substrate

As command substrates in liquid crystal (LC) panels, azopolymer films have been widely studied over past decade. These studies were mainly caused by photoordering and photorefraction effects allowing to control LC alignment. Earlier, the mentioned effects were used separately. In the present study, a layer of azopolymer acts both as photoaligning and photorefractive substrate. The photoordering effect is used to align LCs homogeneously, whereas effect of the specific photorefraction is employed to modify boundary conditions. The latter ones were spatially modulated by the sample exposure to interference patterns formed by two coherent laser beams. Multiple orders of diffraction are observed in samples tilted with respect to the beam incidence bisector when the samples are biased by a dc external electric field with the intensity close to the Frederiks threshold. Possible grating recording mechanisms are discussed.

Photoinduced Phenomena in Quantum Paraelectric Oxides by Ultraviolet Laser Irradiation

A photo-induced effect in the quantum dielectric system, such as SrTiO3, KTaO3, and CaTiO3, has been investigated under rather small external DC electric field. The dielectric measurement was performed under ultraviolet (UV) laser excitation combined with DC electric field. The gigantic photo-induced effects of dielectric properties of the quantum paraelectric systems have been firstly observed in the perovskite-type materials. The photoinduced dielectric effect was obtained as a function of DC electric field under constant UV irradiation.

Electrical conduction and polarization in PbWO4 crystals

The regularities of ion-electron processes in an undoped PbWO4 single crystal upon transition to a quasi-equilibrium state in an external dc electric field with a linear variation in the temperature in the range 290–600 K are investigated using different methods. The total conductivity, thermally stimulated polarization current, and thermally stimulated depolarization current are measured. It is assumed that the temperature dependence of the conductivity can be described within the theory of small-radius polarons. The thermally stimulated polarization (depolarization) currents are interpreted in terms of the space-charge (peaks of the current in the range 400–550 K) and dipole (peaks of the current in the range 290–370 K) mechanisms of generation of a polarization charge in the sample. The inference is drawn that the dominant contribution to the dipole polarization is made by dipolons, namely, doubly charged (cation-anion) vacancy pairs coupled through electrostatic interaction. The basic parameters of relaxation phenomena and charge transfer are calculated.

Electric-Field-Induced Reorientation of a Ferroelectric Liquid Crystal Molecule without a Carboxylate Group near the Stereocenter Studied by Time-Resolved Infrared Spectroscopy Combined with Normalized Sample−Sample Two-Dimensional Correlation Spectroscopy

The orientation dynamics of a ferroelectric liquid crystal (FLC) with a naphthalene ring and without a carboxylate group near the stereocenter (FLC-2) during the electric-field-induced switching has been investigated by time-resolved infrared (IR) spectroscopy combined with normalized sample−sample two-dimensional (2D) correlation spectroscopy. To reveal the orientation dynamics, we have proposed a normalized sample−sample 2D correlation spectroscopy that is calculated by normalizing a sample−sample 2D correlation spectrum over every column or row. An important advantage of the normalized sample−sample 2D correlation spectroscopy over sample−sample 2D correlation spectroscopy is that the excessive information is deleted and more precise information therefore can be extracted even from spectra with a rather low signal-to-noise ratio. The normalized sample−sample 2D correlation spectroscopy allows us to explore the differences in the dynamics of each segment more clearly than the usual sample−sample 2D correlation spectroscopy. Time-resolved IR spectra of FLC-2 in a planar-aligned cell were measured over two delay time ranges from 0 to 150 μs and from 200 to 350 μs at an interval of 10 μs with the polarization angle of 45.0° under a rectangular electric field of ±3 V with a 2.5 kHz repetition rate in the smectic-C* (Sm-C*) phase at 115 °C. The normalized sample−sample correlation spectroscopy was applied to these time-resolved spectra. We explored the reorientation process of the alkyl chains, the core, and the carboxylate group of FLC-2 in the positive and negative half-periods of the electric-field-induced switching. It has been found from the present study that the reorientation track of the core in the positive half-period is different from that in the negative half-period, while the reorientation tracks of the CO dipole moment and alkyl chains are very similar between the positive and negative half-periods. The present study has also revealed that the orientation profile of the core moiety is different from those of the alkyl chains and the CO dipole moment, and the difference in the profile depends on the change of dc electric field from −3 to +3 V and from +3 to −3 V at an interval of 0.25V . It seems that the core moiety functions in the presence of memory properties. Furthermore, a tilt angle for FLC-2 with a naphthalene ring and without a carboxylate group near the stereocenter is smaller than other similar FLCs with a naphthalene ring and a carboxylate group near the stereocenter. It has been suggested from the analysis of the polarization-angle dependent spectra under the external dc electric field of two polarities that the carboxylate group near the stereocenter plays an important role in forming a large tilt angle and that the carboxylate group in the core moiety is responsible for the emergence of ferroelectricity.

Optical activity of electrorheological fluids under external electric field

The optical activity of electrorheological (ER) fluids under an external dc electric field was investigated. According to the nonhomogeneous structure model of ER fluids, we propose an expression of rotation angle from Maxwell’s equations and Fresnel reflection. The optical activity of several kinds of ER fluids was measured by varying an applied electric field, the angle θ, and weight concentrations. The experiments show that the rotation angle increases with the concentration and electric field, and it first increases, passes through a maximum at an optimum θ, then monotonically decreases with θ. The experimental results are in qualitative agreement with our theoretical simulations. It is thought that the structure symmetry breaking of ER fluids under an external electric field may be the origin of the optical activity.

Dielectric Enhancement in Quantum Paraelectric SrTiO 3 by UV Laser Irradiation under DC Electric Field

The gigantic photo-induced effect of dielectric property in the quantum dielectric material SrTiO 3 has been observed under rather small external DC electric field. The dielectric measurement was performed under UV laser excitation with energy above the band gap combined with a DC electric field. The photo-induced effect without a DC electric field has been enhanced with increasing of the AC electric field.

Reduction of the space-charge field in photorefractive crystals

The space-charge-field amplitude inside photorefractive crystals was evaluated using three different experimental techniques: (i) two-wave mixing gain measurements, (ii) direct phase demodulation under external dc-electric field, and (iii) phase demodulation under ac-field with proper polarization filtering. The experimental data could be simultaneously fitted with the theory in the frame of the traditional one-level photorefractive model only if an additional reduction of the space-charge field is assumed. The traditional model fails to explain appearance of this reduction factor. Measurements were carried out with Bi 12TiO 20 and GaP photorefractive crystals.

Electrorheological properties of poly(lithium‐2‐acrylamido‐2‐methyl propane sulfonic acid) suspensions

AbstractIn this study, poly(2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid) (PAMPS) was synthesized using potassium persulfate (K2S2O8) as initiator. PAMPS (Mn = 36,000 g/mol) was partially converted to a lithium salt (PAMPS–Li), and particle size was determined to be 40 μm. Suspensions of PAMPS–Li at various concentrations were prepared in silicone oil, mineral oil, dioctylphthalate (DOP), and trioctyltrimellitate (TOTM) insulating oils. Colloidal stabilities of these suspensions were determined at 20 and 80°C. The PAMPS–Li suspensions were observed to provide an electrorheological (ER) response upon the application of an external dc electric field. ER properties of these suspensions were investigated at various shear rates (γ˙) and electric field strengths (E). Further, effects of polar promoters and high temperature on ER activity were determined, and excess shear stresses (Δτ) were calculated. A shear‐thinning non‐Newtonian viscoelastic behavior was observed for the PAMPS–Li suspensions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1106–1112, 2002

Transient and steady linear response of dielectric particles in a high bias fieldsubject to a weak AC probe field

A dilute suspension of spherical particles with permanent electric dipole momentand additional polarizability is subject to a strong DC external electric field. Inaddition, a weak AC probe field is suddenly switched on at time t = 0. Thelinear response of the polarization is described by solving the first-orderSmoluchowski equation for the orientational distribution function. Both thetransient and the steady response are obtained. The transient is given explicitly asa sum of exponentially decaying functions of time characterized by a set of decayrates and associated amplitudes. A fast numerical method is used to calculate thespectrum of decay rates and the amplitudes of the decaying modes from theLaplace transform of the perturbed distribution function. The steady response ischaracterized by a complex susceptibility which is given explicitly in terms of thedecay rates and amplitudes that characterize the transient. The transient solution,its mean decay time and the susceptibility are all given as explicit functions of thefrequency of the probe field. The results for simple permanent dipoles arecompared with the much richer results for dipoles with polarizability as well.

Phonon amplification in a quasi-one-dimensional GaAs quantum channel

We propose a calculation for the amplification coefficient γqof acoustical phonons interacting with electrons in a quasi-one-dimensional GaAs channel subjected to an external dc electric field. Two regimes of temperatures have been investigated and it has been found, by considering only intrasubband transitions, that the amplification coefficient for a particular frequency, and for phonons propagating along the channel length ( z -axis), is a step-like function of the applied field at low temperatures. For high temperatures the amplification coefficient shows an exponential behavior as a function of the applied electric field. Furthermore, provided the one-dimensional quantum channel has high electron mobility values, coherent acoustic-phonons can be amplified in modest electric fields.