Uniform External Electric Field Research Articles

External uniform electric field removing the flexoelectric effect in epitaxial ferroelectric thin films

Using the modified Landau-Ginzburg-Devonshire thermodynamic theory, it is found that the coupling between stress gradient and polarization, or flexoelectricity, has a significant effect on ferroelectric properties of epitaxial thin films, such as polarization, free-energy profile and hysteresis loop. However, this effect can be completely eliminated by applying an optimized external, uniform electric field. The role of such uniform electric field is shown to be the same as that of an ideal gradient electric field which can suppress the flexoelectricty effect completely based on the present theory. Since the uniform electric field is more convenient to apply and control than the gradient electric field, it can be potentially used to remove the flexoelectric effect induced by the stress gradient in epitaxial thin films and to enhance the ferroelectric properties.

Induced displacive transition in heterogeneous materials

A model of heterogeneous, composite material is introduced, consisting of randomly distributed identical structural micro-domains endowed with electric charges or dipoles. Two cases are presented, one corresponding to a tightly packed (dense) material, another corresponding to highly-dispersed, small domains. The polarizability is computed in both cases, under the action of an external uniform electric field oscillating in time (a quasi-stationary field), and it is related to the displacement of the micro-domains from their positions of local equilibrium (translations or rotations). It is shown that the polarizability (or electric susceptibility) can exhibit characteristic (resonance) frequencies in the radio-frequency range and, even for moderate external fields, the material can undergo a displacive transition (similar to a ferroelectric transition), governed by non-linearities in the interaction energy of the micro-domains. The shift in the characteristic frequencies of the polarizability is estimated, as caused by the displacive modification.

Coupled-channel theory of photoionization microscopy

We develop a quantum-mechanical coupled-channel theory to simulate spatial distributions of electron current densities, produced in photoionization for nonhydrogenic atoms in the presence of a uniform external electric field. The coupled Schr\"odinger equations are numerically solved using the renormalized Numerov method. The expression for the outgoing wave function for photoelectrons ejected from the nonhydrogenic atomic source is derived. The theory is applied to investigations of photoionization for ground-state Li atoms. The distributions of electron current densities are computed and compared to the corresponding experimental images. Excellent agreement is obtained. It is, furthermore, found that the presence of the nonhydrogenic residual ion significantly changes the differential cross sections and/or electron current densities with respect to the hydrogenic case. Finally, the implications of the presence of the atomic core for quantum resonance tunneling are also analyzed.

Electric potential distribution near nanocone arrays on metal substrates

Based on the nanostructured surface model, where conical nanoparticle arrays grow out symmetrically from a plane metal substrate, a theoretical model of the local electric potential near nanocones is built when a uniform external electric field is applied. In terms of this model, the electric potential distribution near the nanocone arrays is obtained and given by a curved surface using a numerical computation method. The computational results show that the electric potential distribution near the nanocone arrays exhibit an obvious geometrical symmetry. These results could serve as a basis for explaining many abnormal phenomena, such as the abnormal infrared effects (AIREs) which are found on nanostructured metal surfaces, as well as a reference for investigating the applications of nanomaterials, such as nanoelectrodes and nanosensors.

Electron Raman scattering in asymmetrical multiple quantum wells system with an external electric field

The differential cross-section for an electron Raman scattering process in a semiconductor multiple GaAs/AlGaAs quantum well with the presence of an external uniform electric field is calculated for T=0K. We assume single parabolic conduction band with one electron. The emission spectra and the effect for different electric field values are discussed. Singularities in the spectra are found and interpreted. The ERS studied here can be used to provide direct information about the electron band structure of these systems.

Partial electrical potential distribution around nanospheres in metallic nanostructured films

In light of the nanostructured surface model, where half-spherical nanoparticles grow out symmetrically from a plane metallic film, the mathematical model for the partial electrical potential around nanospheres is developed when a uniform external electric field is applied. On the basis of these models, the three-dimensional spatial distribution of the partial electrical potential is obtained and given in the form of a curved surface using a numerical computation method. Our results show that the electrical potential distribution around the nanospheres exhibits an obvious geometrical symmetry. These results could serve as a reference for investigating many abnormal phenomena such as abnormal infrared effects, which are found when CO molecules are adsorbed on the surface of nanostructured transition metals.

Elecrohydrodynamical characteristics of liquid film motor driven by a square-wave electrophoresis electric field

Liquid film motor as a novel experimental device will play an important role in basic research and technology applications. In-depth theoretical studies on its electro-hydrodynamics (EHD) motions under various conditions are of great significance. In current paper, the dynamical characteristics of the liquid film motor driven by a square-wave electrophoresis electric field perpendicular to a uniform constant external electric field are investigated. Space-time dependence of the film's rotation linear velocity is derived analytically. The theoretical results indicate that a symmetrical reciprocating rotation in the film gradually converts to a vibration as the frequency of the electrophoresis electric field increases. This not only helps us understand the physical origin of the vibration of the liquid film motor, but also provides a new option to design a liquid film mixer in the application.

Boundary layer velocity distribution of two special ferromagnetic fluid

Poiseuille flow refers to the incompressible viscous laminar flow in a pipe with two fixed plate. Assuming the ferrofluid is flowing along the x axis direction, with external uniform magnetic field B0 along y axis direction and external uniform electric field E0 along z axis direction. The plat plates are fixed in the (x;z) plane and the width between the two plates is 2a. The velocity and magnetic induction of the ferrofluid are given as follows: V=(u(y),0,0), B=Bx(y), By(y),B0+By(y),0). Suppose that ∂p/∂x is irrelevant to y and ∂p/∂y is irrelevant to x, let Fa=a√σ/η(B0+By(y)), then, for poiseuille flow of ferromagnetic fluid we get its boundary layer velocity. Morever, Couette flow of ferromagnetic fluid is also investigated.

Thermo-electric-induced dichroism in ion-exchanged glasses: a candidate mechanism for the alignment of silver nanoparticles

In the present work, the alignment mechanism of silver nanoparticles on the surface of a heated ion-exchanged glass, in presence of an external uniform DC electric field $(\vec{E}_{0})$ parallel to the surface of the sample, is studied. At high temperature, the ionic silver clusters reduce to neutral ones and move toward the surface. Simultaneously, due to the external electric field the clusters interact with other ones as induced electrical dipoles. This leads to alignment of nanoparticles along $\vec{E}_{0}$ and formation of a chain-like conductive structure, which makes the sample dichroic. Taking into account the matrix surface viscosity and using the method of image dipoles to model the influence of the substrate on the dipole interactions, we give an interpretation about the relative equilibrium positions of generated nanoclusters and consequently the formation mechanism of the chain-like structure on the surface of the ion-exchanged glass.

On generation of boost pairs by a constant electric field

The problem of quantization of a complex scalar field in an external constant uniform electric field is considered in the basis of boost modes. The in- and out-regions in the Minkowski space are deter-mined, and the complete sets of in- and out boost modes describing particles and antiparticles are constructed. The number of boost pairs generated by the field from vacuum in each mode, as well as the total number of produced particles, is calculated.

Constant electric field simulations of the membrane potential illustrated with simple systems

Advances in modern computational methods and technology make it possible to carry out extensive molecular dynamics simulations of complex membrane proteins based on detailed atomic models. The ultimate goal of such detailed simulations is to produce trajectories in which the behavior of the system is as realistic as possible. A critical aspect that requires consideration in the case of biological membrane systems is the existence of a net electric potential difference across the membrane. For meaningful computations, it is important to have well validated methodologies for incorporating the latter in molecular dynamics simulations. A widely used treatment of the membrane potential in molecular dynamics consists of applying an external uniform electric field E perpendicular to the membrane. The field acts on all charged particles throughout the simulated system, and the resulting applied membrane potential V is equal to the applied electric field times the length of the periodic cell in the direction perpendicular to the membrane. A series of test simulations based on simple membrane-slab models are carried out to clarify the consequences of the applied field. These illustrative tests demonstrate that the constant-field method is a simple and valid approach for accounting for the membrane potential in molecular dynamics studies of biomolecular systems. This article is part of a Special Issue entitled: Membrane protein structure and function.

Enhancement of the electron electric dipole moment in Eu2+

Recently, the ferroelectric Eu${}_{0.5}$Ba${}_{0.5}$TiO${}_{3}$ was suggested for experimental searches of the electron electric dipole moment. To analyze results of the experiment and interpret them in terms of fundamental constants, the effective electric field ${E}_{\mathrm{eff}}$ acting on unpaired electrons of the europium cation should be calculated. In the present paper we consider Eu${}^{2+}$ cation in the uniform external electric field ${E}_{\mathrm{ext}}$ as the first step and important starting point toward the calculation of ${E}_{\mathrm{eff}}$ in the real solid. We have performed high-level electronic structure correlation calculations using the coupled clusters theory compared to other approaches. The calculated value of the field enhancement coefficient is $K={E}_{\mathrm{eff}}/{E}_{\mathrm{ext}}=\ensuremath{-}4.6$.

Molecular dynamics simulations of phase transition of lamellar lipid membrane in water under an electric field

Molecular dynamics simulations were conducted to investigate phase behaviors of lamellar lipid membranes in water under a uniform external electric field. Poration, deformation and fusion of membranes were induced and water/membrane interfaces changed from perpendicular to parallel to the electric field. The hydration level of the lipids determined whether the final phase was the lamellar or inverted columnar structure. The simulations provide insights into phase transitions of amphiphile solutions in electric fields and mechanisms of cell electrofusion.

Dissipative solitons in carbon nanotubes

The possibility of analogs of dissipative solitons occurring in arrays of carbon nanotubes under the action of a high-frequency external uniform electric field on the array has been established theoretically. The electromagnetic field has been considered in terms of the Maxwell equations, and the conduction electrons in carbon nanotubes have been described by the Boltzmann kinetic equation in the relaxation-time approximation. The external ac electric field serves for energy pumping of the electronic subsystem, whereas a finite relaxation time leads to energy dissipation. The generation of a periodic sequence of electromagnetic pulses has been revealed. This sequence can be used for producing terahertz frequencies.

Charges on the surface of a lentil cavity in a two-dimensional homogeneous conductor

The linear charge density on arc segments of a lentil cavity in a two-dimensional homogeneous conductor in a uniform external electric field is determined analytically. A singularity of the current density on the edges of the segments makes the resultant relations a helpful test for numerical computational algorithms.

Shear and flexoelectric deformation effects on the dynamic structure factor of a nematic liquid crystal

We use a fluctuating hydrodynamic description to calculate the orientation (director) correlation function of hydrodynamic fluctuations for a nematic liquid crystal in a non-equilibrium steady state (NESS). This state is produced by both, a planar shear flow and an external uniform electric field, which induces an elastic deformation through the so-called flexoelectric effect. We analyze the effects of these external gradients to estimate the changes on the light scattering spectrum produced by both gradients with respect to its equilibrium shape. We find that these non-equilibrium effects induce long-range effects on the orientation correlation with a k-dependence k − 2 and k − 3 , respectively, giving rise to an asymmetry of the spectrum. This consists of an increment of its maximum and a displacement in the frequency shift space. These changes are proportional to the magnitude of the external gradients and also depend on the relative orientation of the gradients with respect to the wave vector. We find that for MBBA, the shear flow can produce significant increases on the dynamic structure factor of 9.6%, for normalized velocity gradients of the order 0.1–0.5. The flexoelectric effect produces only small changes on the structure factor, which are about two orders of magnitude smaller with respect to those due to the presence of the shear flow. Our analysis suggests that the effects produced on dynamic correlations by the flexoelectric effect would be hard to observe experimentally, while those due to the shear flow might be detectable.

Dynamics of electron wave propagation in photoionization microscopy. II. Quantum-mechanical formulation

Complementary to the semiclassical method developed in the preceding paper, here we develop a quantum-mechanical approach to characterize propagation of electron waves to large distances in photoionization microscopy of hydrogen atoms in uniform external electric fields. A formula for outgoing electron waves from the atomic source produced in photoionization has been derived. Spatial distributions of electron probability densities can be determined using the obtained formula. The electron waves that propagate to a large distance due to photoionization from the $n=2$ initial state of hydrogen atoms in electric fields has been calculated and the resulting probability densities are presented. Comparison with semiclassical results is made, and they are found to be in good agreement. A detailed analysis is given of strong quantum tunneling effects found in our calculations.

Accurate Computation of Electric Field Enhancement Factors for Metallic Nanoparticles Using the Discrete Dipole Approximation

We model the response of nanoscale Ag prolate spheroids to an external uniform static electric field using simulations based on the discrete dipole approximation, in which the spheroid is represented as a collection of polarizable subunits. We compare the results of simulations that employ subunit polarizabilities derived from the Clausius–Mossotti relation with those of simulations that employ polarizabilities that include a local environmental correction for subunits near the spheroid’s surface [Rahmani et al. Opt Lett 27: 2118 (2002)]. The simulations that employ corrected polarizabilities give predictions in very good agreement with exact results obtained by solving Laplace’s equation. In contrast, simulations that employ uncorrected Clausius–Mossotti polarizabilities substantially underestimate the extent of the electric field “hot spot” near the spheroid’s sharp tip, and give predictions for the field enhancement factor near the tip that are 30 to 50% too small.

Symmetry breaking in cationic polymethine dyes, part 1: Ground state potential energy surfaces and solvent effects on electronic spectra of streptocyanines

AbstractCharge localization and dynamics in conjugated organic molecules, as well as their spectral signatures are of great importance for photonic and photovoltaic applications. Intramolecular charge delocalization in polymethine dyes occurs through π‐conjugated bridges and contributes to the appearance of low‐energy excited states that strongly influence their linear and nonlinear optical (NLO) properties. When the chain length in symmetrical cations exceeds the characteristic size of the soliton, the positive charge may localize at one of the terminal groups of the molecule and induce symmetry breaking of both the electron density distribution and molecular geometry. This charge localization is coupled with molecular vibrations and solvent effects. We investigated the mechanism of symmetry breaking in a series of cationic streptocyanines with different conjugated chain length and qualitatively predicted their electronic absorption spectra. This class of organic molecules is chosen as a model system to develop methodology which can subsequently be used to evaluate more complicated compounds for NLO applications. Our calculations show that the minimum number of vinylene groups in the conjugated chain necessary to break the symmetry of streptocyanines is eight in the gas phase and six in cyclohexane. We constructed the ground state potential energy surface (PES) in two dimensions using symmetry breaking and symmetry adapted coordinates. These were defined as the difference and the sum of the two central carbon–carbon bonds, respectively. This PES was found to have two equivalent minima for systems with symmetry breaking. The energy barrier between these two minima was estimated in the gas phase and in solution, which was taken into account by the polarizable continuum model. Charge localization in each minimum was found to be asymmetric. It is additionally stabilized by the solvent reaction field, which increases the energy barrier. The electronic absorption spectrum in solution is red shifted as compared to the gas phase. As the symmetry breaks, additional excited states with large oscillator strengths appear in the electronic spectrum. Geometry optimization and spectral predictions were also performed in a uniform external electric field in order to simulate nonequilibrium solvation effects due to the finite relaxation time of solvent molecules. Two asymmetric minima with different depths appear on the resulting PES. The lower minimum has charge localized at one of the two molecular terminal groups which is additionally stabilized by the solvent field, while the higher one has charge localized on another terminal group. This finding demonstrates the possibility that two forms with different charge distributions coexist in polar solvents. Our results suggest that nonequilibrium solvation may be a cause of absorption band broadening and splitting. This work is a first step in a larger study aimed at the analysis of the linear and nonlinear properties of long π‐conjugated systems of interest for NLO applications and plastic photovoltaics. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Electrostatic response of a half-disk

This article studies the response of a half-disk exposed to an external uniform static electric field. A semianalytical method is presented for computing the potential for a geometry consisting of two conjoined half-disks with different permittivities. The method is based on analytical series expansions with coefficients obtained as a numerical solution of a matrix equation. We consider the polarizability of a single dielectric half-disk and discuss a duality relation observed in 2D polarizability. We also study the surface plasmons supported by a negative-permittivity half-disk.