High External Electric Field Research Articles

Micro-Bubble Phenomenon in Nanoscale Water-based Lubricating Film Induced by External Electric Field

The effect of an external electric field (EEF) on water-based thin films has been investigated. Some micro-bubbles emerging around the edge of the Hertz contact region in the films of deioned water and polyethylene glycols (PEG) aqueous solutions have been observed. A higher EEF intensity is needed at which the micro-bubbles begin to emerge after the EEF is applied on the liquid film, which is defined as the threshold EEF intensity. The threshold EEF intensity increases with the molecular weight of PEG solution at lower molecular weight. There is a maximum value when the molecular weight reaches 10,000 Da, beyond which the threshold EEF intensity tends to decrease. The threshold EEF intensity also increases with the concentration of PEG solution. Micro-bubble emerging at negative EEF is easier than at positive EEF. The micro-bubble emerging in the film of deioned water is sensitive to the variation of EEF intensity, and disappears eventually as time progresses.

Field-assisted oxidation of rhodium

The oxidation of nanosized rhodium facets is investigated in the presence of a high external electric field with field ion microscopy experiments (FIM). Corresponding density functional theory (DFT) calculations were done on Rh(0 0 1), Rh(0 1 1) and Rh(1 1 1). A cross-like granular structure is obtained with FIM when the electric field is increased from 11 to 12.3 V/nm, which strongly indicates that the field promotes the oxidation of the tip. The DFT calculations confirm this scenario with a corresponding reduction of the activation barrier for oxygen incorporation into the surface of an oxide layer.

Surface electric field manipulation of the adsorption kinetics and biocatalytic properties of cytochrome c on a 3D macroporous Au electrode

Upon adsorbing on a solid-state substrate, water-soluble proteins are prone to denaturation and deterioration of their functions due to the conformation change. The surface electric field of a conductive substrate is one of the important factors that influence the character of adsorbed proteins. In this work, a 3D macroporous gold electrode has been prepared and served as the working electrode to study the influence of surface electric field on the adsorption kinetics and conformation of the adsorbed cytochrome c (cyt-c) with the help of electrochemical, in situ electrochemical IR spectroscopic, atomic force microscopic, and contact angle measurements. The external electric field creates excess surface charge which can manipulate the adsorption rate of proteins on the substrate by the enhanced electrostatic interactions between the electrode and protein patches by coupling with complementary charges. The amount of immobilized cyt-c with electrochemical activity on the 3D macroporous gold electrode showed a minimum at potential of zero charge (PZC) and it increased with increasing net excess surface charge. Higher electric field could influence the conformation and the corresponding properties such as direct electrochemistry, bioactivity, and surface character of the adsorbed cyt-c molecules. However, high external electric field leads to damage of the protein secondary structure. This study provides fundamentals for the fabrication of biomolecular devices, biosensors, and biofuel cells through electrostatic interactions. [figure: see text] Two cases are illustrated for the protein immobilized on electrode surfaces: a retention of protein structure under moderate excess surface charge, b denaturation and conformation change of proteins adsorbed at high excess surface charge, e.g., due to the higher external electric field.

Transient electron excitation in laser-induced plasma-assisted ablation of transparent materials

We investigate the mechanism of laser-induced plasma-assisted ablation (LIPAA), by which high-quality and high-efficiency ablation of transparent materials, such as glass, can be performed with a single conventional pulsed laser. The laser-induced plasma induces transient absorption of the laser beam (532nm) by the glass substrate. The origin of the transient absorption is electron excitation by ions with kinetic energy more than approximately 10eV in the plasma, which is observed by measuring transient polarization change in the glass substrate applied with a high external pulsed electric field during the plasma-assisted electron excitation (plasma-conductivity measurement). A possible mechanism of LIPAA is proposed based on the results obtained.

Possible Isostructural Transitions in the Ferroelectric Liquid Crystals in High External Electric Fields

ABSTRACT Two different types of isostructural transitions between two homogeneously tilted ferroelectric liquid crystalline structures are discussed. A strong biquadratic coupling between the tilt and the polarization leads to the discontinuous jump of the tilt magnitude when the electric field is increased. A strong anisotropic quadratic coupling with the electric field leads to the continuous structural transition associated with a change of the direction of the tilt.

Antiferroelectric Properties Induced by External Electric Field

ABSTRACT A theoretical possibility of the re-entrancy of the antiferroelectric properties in antiferroelectric liquid crystals under the influence of the high external electric field is discussed.

Retention of nativelike conformation by proteins embedded in high external electric fields

In this Communication, we show that proteins embedded in high external electric fields are capable of retaining a nativelike fold pattern. We have tested the metalloprotein azurin, immobilized onto SiO2 substrates in air with proper electrode configuration, by applying static fields up to 10(6)-10(7) Vm. The effects on the conformational properties of protein molecules have been determined by means of intrinsic fluorescence measurements. Experimental results indicate that no significant field-induced conformational alteration occurs. Such results are also discussed and supported by theoretical predictions of the inner protein fields.

Switching fatigue of ferroelectric layered-perovskite thin films: temperature effect

We study the switching fatigue behaviors of ferroelectric layered-perovskite oxide films, including SrBi 2Ta 2O 9, Bi 3.15Nd 0.85Ti 3O 12 and Bi 3.25La 0.75Ti 3O 12 deposited on Pt/TiO 2/SiO 2/Si substrates, at various temperatures. It is found that the damaged ferroelectric polarization and dielectric response in the fatigued films can be easily rejuvenated under a high external electric field, for which the localization of the defect and charge accumulation is argued to be responsible. It is proposed that the probability of fatigue rejuvenation can be characterized by the kinetics of domain wall pinning and depinning which depends on the stability of perovskite-like slabs against defect/charge diffusion and/or the self-regulation of the (Bi 2O 2) 2+ layer to compensate for space charges.

Site-dependent atomic response on an external high electric field in GaPO4: new insights into understanding the inverse piezoelectric effect

Site-dependent atomic response on an external high electric field in GaPO₄: new insights into understanding the inverse piezoelectric effect

Electric Field Effects on Photoconductivity and Electronic Absorption Spectra of Photogeneration Sites in Amorphous Molecular Semiconductors

Field dependences of photogeneration quantum yields of charge carriers in films of amorphous molecular semiconductors at high external electric field strengths cannot be always explained in terms of the Onsager or the Poole–Frenkel model, which do not consider the effect of an electric field on basic parameters of these materials. It is assumed that an external electric field shifts the electron density in molecules from its equilibrium distribution, thus altering the probability of electronic transitions. The assumption has been verified in studying the effect of an external electric field on the absorption spectra of poly(N-epoxypropylcarbazole) films doped with a merocyanine dye. Correlation between the theoretical and experimental results has been obtained.

Coupling effects for counterpropagating light beams in lithium niobate crystals studied by grating translation technique for extremely high external electric fields

The grating translation technique (GTT), which employs a momentary shift of light fringes during holographic recording, is a powerful tool for characterization of nonlinear materials. Earlier, it was used in the transmission geometry. We formulate the main relations of GTT for the reflection case. These allow us to determine in situ the real and imaginary parts of the coupling strength and to detect the formation of refractive-index and absorption gratings. We apply GTT to determine the photorefractive characteristics of two-wave coupling in z-cut iron-doped lithium niobate crystals for an extremely small grating spacing (Λ≃105 nm) and extremely large externally applied electric fields (up to 650 kV/cm). Stabilization of the light fringes, crucially important in the reflection geometry, has been achieved with the use of an electronic feedback loop. We prove that the feedback introduces a frequency detuning between the light beams and modifies strongly the nonlinear response.

Beam fanning reversal in the ferroelectic relaxor Sr0.61Ba0.39Nb2O6 at high external electric fields

Beam fanning has been studied in the cerium-doped ferroelectric relaxor strontium–barium–niobate (Sr0.61Ba0.39Nb2O6:Ce, SBN:Ce) under the application of high external electric fields. Spatial reversal in the distribution of the scattered light is achieved both below and above the phase transition. It is shown that the photorefractive response in SBN strongly depends on the state of the polar structure of the crystal, which can be controlled by external fields. Coherent illumination of the crystal greatly facilitates the repoling process, causes a considerable refinement of the domain order in the ferroelectric phase and assists the stabilization of the polar structure in the relaxor regime. The model of scattering centers associated with refractive index anomalies located on domain walls is applied to receive detailed information about the distribution of initial seed scattering in the crystal bulk and the efficiency of nonlinear amplification of the scattering.

Feedback-controlled two-wave coupling in reflection geometry: application to lithium niobate crystals subjected to extremely high external electric fields

An active stabilization of photorefractive two-wave coupling by means of an electronic feedback loop has been used extensively during recent years in transmission geometry. It leads to 100% diffraction efficiency η and also to periodic states instead of familiar steady states. We investigate the feedback operation in the case of reflection geometry, especially for iron-doped lithium niobate (LiNbO3:Fe) crystals. This includes formulation of the feedback equations, numerical analysis of the operation regimes for LiNbO3 crystals, and comparison between theory and experiment, which is performed in the range of applied electric fields from 0 to 650 kV cm-1. The main findings are as follows: (i) the feedback does not lead to periodic states, (ii) it modifies the photorefractive response by introducing a frequency shift and maximizes η, and (iii) there is a close relation between the enhancement of η and the resonant excitation of space-charge waves predicted earlier in ferroelectric materials.

Electric field induced charge density variations in partially-ionic compounds

Using a modulation technique and synchrotron radiation, we investigated the charge density variations in cubic ZnSe and trigonal SiO 2 induced by an external high-electric field E applied along the [111] and [11.0] direction, respectively. Selecting particularly weak reflections, we observed an almost linear variation of the integrated intensity versus E changing by up to 2% at | E|=3 kV/mm. For both crystals, the displacements of the relative ion positions within the unit cell exceed the piezoelectric induced variation of the unit cell parameters by at least one order of magnitude. The measured intensity variations of ZnSe can be explained by the opposite displacement of the zinc and selenium ions towards the field direction breaking the stiff tetrahedral coordination of the chemical bond. For quartz, the electric field initiates a displacement of those oxygen ions only where the O–Si bond is directed oblique to the field direction. The other oxygen ions and the silicon positions remain nearly unchanged. Thus, the ionic arrangement is described mainly by a change in the O–Si–O bonding angles.

Photorefractive InGaAs/GaAs multiple quantum wells in the Franz–Keldysh geometry

We fabricate semi-insulating InGaAs/GaAs multiple quantum wells and observe the excitonic enhancement of the photorefractivity in the Franz–Keldysh geometry at wavelengths of 0.92–0.94 μm. A maximum two-wave mixing gain of 138 cm−1 and a maximum diffraction efficiency of 1.5×10−4 are obtained. The saturation intensity and the spatial resolution are also measured by four-wave mixing. The diffraction efficiency is saturated at a high external electric field. The dominant cause of this saturation is the deviation of the excitonic electroabsorption from its quadratic law.

New Insights on Persistent Nonphotochemical Hole Burning and Its Application to Photosynthetic Complexes

Nonphotochemical hole burning (NPHB) at low temperatures of the electronic absorption bands of molecular chromophores imbedded in amorphous solids (glasses and polymers) and in proteins is a striking manifestation of configurational tunneling triggered by electronic excitation. The current mechanism of NPHB has it due to a hierarchy of relaxation events that begin in the outer shell and involve the intrinsic two-level systems (TLSint) of the glass and terminate in the inner shell where the rate determining step involving the extrinsic TLS (TLSext) occurs. The TLS correspond to asymmetric intermolecular double well potentials. The TLSext are associated with the chromophore and the inner shell of solvent molecules. The TLSint are intimately associated with the excess free volume of glasses. Their tunneling leads to diffusion of excess free volume. Results for Al-phthalocyanine tetrasulfonate (APT) in hyperquenched glassy water (HGW) and ethanol (HGE) films that provide strong support for the critical role of excess free volume are discussed. Hole spectra of APT/HGW obtained over eight decades of burn fluence reveal that the current mechanism needs to be modified to include multilevel extrinsic systems (MLSext) in order to explain why the antihole (“photoproduct” absorption) lies to the blue of the burn frequency for sufficiently high burn fluences, an intriguing up-conversion process. The spectra also reveal, for the first time, that the zero-phonon hole (ZPH) profile is non-Lorentzian. This is shown to be a natural consequence of the interplay between the three distributions that result in dispersive hole growth kinetics. They are associated with the tunnel parameter λ of the TLSext, the angle α between the laser polarization and transition dipole, and off-resonant absorption of the zero-phonon line (the ω distribution). Theoretical simulations of hole growth data for APT/HGW obtained over six decades of burn fluence show that the λ distribution is of primary importance, describing well the first 80% of the saturated burn. The paper ends with an application of NPHB combined with high pressure and external electric (Stark) fields to the critically important “red” antenna states of photosystem I. The addition of pressure and Stark fields enhances the already impressive selectivity of NPHB. The results show that the linear pressure shift, permanent dipole moment change, and linear electron−phonon coupling are correlated. Of particular importance is that these properties can be used to identify states which involve interacting chlorophyll molecules that possess significant charge transfer character because of electron-exchange coupling. The results also show that the site distribution functions of the antenna states are largely uncorrelated, consistent with the findings for previously studied complexes. This is important because the absence of correlation means that the electronic energy gaps of donor and acceptor states are distributed which, in turn, means that the kinetics can be dispersive under certain conditions.

The influence of uniform pressure and electric field on phase transitions of the Sn 2P2S6 ferroelectric

The investigations of the dielectric and dilatometric properties of the Sn 2P2S6 proper ferroelectrics in the vicinity of the Lifshitz point under high pressure and external electric field was carried out. Based on the investigations on dielectric permeability anomalies the E, T-diagrams at different magnitudes of uniform pressure and p, T, E-diagram of this crystal have been constructed. The pressure behaviour of the coefficients of the thermodynamic potential expansion by degrees of the order parameter is derived.

Multivariate Screening Analysis of Water-in-Oil Emulsions in High External Electric Fields as Studied by Means of Dielectric Time Domain Spectroscopy: III. Model Emulsions Containing Asphaltenes and Resins

The effect of crude oil resins with various polar characters on the stability of w/o model emulsions containing asphaltenes is investigated using a mixture design. The resins were extracted using an adsorption–desorption technique. One asphaltene fraction and four different resin fractions from one European crude oil were used. The stabilities are measured using time-domain dielectric spectroscopy in high external electric field. It is found that resins with different polar character have different effects on the emulsion stability. At asphaltene/resin ratios of 1 and 5 : 3 the resins in some cases lead to an emulsion stability higher than that of a similar emulsion stabilized by asphaltenes only, while at low asphaltene/resin ratios (∼1 : 3) the emulsion stability is reduced by the resins. The effect on emulsion stability of combining two different resin fractions depended on the resin types combined as well as the relative amount of resins and asphaltenes. Also, an increase in the stability of some of the emulsions containing resins and asphaltenes for a period of 50–300 min after the emulsification was observed. This time-dependence of emulsion stability is attributed to the mobility of resins at the oil–water interface and the slow buildup of a stabilizing interfacial film consisting of resins and asphaltenes.

An improved model for ultraviolet- and x-ray-induced electron emission from CsI

A microscopic theoretical model is proposed for calculating the characteristics of ultraviolet photoemission and x-ray secondary electron emission induced from CsI photoconverters. This approach is based on a realistic picture of the basic interactions of photons and induced electrons within the material. Both differential and integral emission characteristics, such as energy spectra and quantum efficiencies, are estimated according to the model and are found to agree, in general, with experimental data. The model-calculated photoemission enhancement under high external electric fields is also considered and is fairly compatible with measured values. The applicability of the model in the field of radiation detectors incorporating solid photoconverters is discussed.

Dielectric constant of water at high electric fields: Molecular dynamics study

Molecular dynamics computer simulations have been carried out for water enclosed between Pt(111) surfaces at high external electric fields. The dielectric constant of water as a function of electric fields has been calculated. Two-dimensional Ewald summation technique has been used for the calculation of long-range Coulombic forces. Simulations with a larger distance between walls, different surfaces, and bulk water have been done to confirm the macroscopic nature of the dielectric constant. Calculated dielectric constants have been compared with those obtained by a theoretical prediction and a recent simulation study.