Orientation Of Electric Dipoles Research Articles

Spontaneous chiral symmetry breaking in polar fluid–heliconical ferroelectric nematic phase

Spontaneous mirror symmetry breaking by formation of chiral structures from achiral building blocks and emergent polar order are phenomena rarely observed in fluids. Separately, they have both been found in certain nematic liquid crystalline phases; however, they have never been observed simultaneously. Here, we report a heliconical arrangement of achiral molecules in the ferroelectric nematic phase. The phase is thus spontaneously both polar and chiral. Notably, the pitch of the heliconical structure is comparable to the wavelength of visible light, giving selective reflection controllable by temperature or application of a weak electric field. Despite bearing resemblance to the heliconical twist-bend nematic phase, this chiral ferroelectric nematic phase arises from electrical interactions that induce a noncollinear orientation of electric dipoles.

The mechanism of the molecular CISS effect in chiral nano-junctions.

The chirality induced spin selectivity (CISS) effect has been up to now measured in a wide variety of systems but its exact mechanism is still under debate. Whether the spin polarization occurs at an interface layer or builds up in the helical molecule is yet not clear. Here we have investigated the current transmission through helical polyalanine molecules as a part of a tunnel junction realized with a scanning tunneling microscope. Depending on whether the molecules were chemisorbed directly on the magnetic Au/Co/Au substrate or at the STM Au-tip, the magnetizations of the Co layer had been oriented in the opposite direction in order to preserve the symmetry of the IV-curves. This is the first time that the CISS effect is demonstrated for a tunneling junction without a direct interface between the helical molecules and the magnetic substrate. Our results can be explained by a spin-polarized or spin-selective interface effect, induced and defined by the helicity and electric dipole orientation of the molecule at the interface. In this sense, the helical molecule does not act as a simple spin-filter or spin-polarizer and the CISS effect is not limited to spinterfaces.

Structural and dielectric relaxation studies of 1, 4, and 1, 3 -butanediol–1, 4-dioxane mixtures using TDR technique

Time domain reflectometry (TDR) was used to examine the complex dielectric permitivity spectra (CPS) of binary mixtures of 1,4, and 1,3 butanediol (BD) with 1,4 Dioxane (Dx) at high frequencies (10 MHz–50 GHz). Both systems show the Cole–Davidson type of relaxation process. The least squares fit (LSF) method is applied to compute dielectric relaxation parameters from the CPS. The interest of the ongoing research is to understand the molecular associations, orientation of electric dipoles, and change in electric dipole density in the liquid mixture with the help of excess dielectric parameters, Bruggeman factor (fB) and the Kirkwood correlation factor for both systems.

Study of Dielectric Relaxation and Hydrogen Bonding Interaction of 1, 4-Butanediol-1, 4-Dioxane Mixture using TDR Technique

The complex permittivity spectra of 1, 4-butanediol -1, 4-dioxane binary mixtures have been measured in the frequency range from 10MHz to 30GHz using the time domain reflectometry (TDR) technique. The complex permittivity spectra show the Cole-Davidson type relaxation. The static dielectric constant and relaxation time at various temperatures have been obtained from complex permittivity spectra by using the nonlinear least squares fit method. The orientation of electric dipoles and solute-solvent interaction in the liquid mixture was confirmed from the excess, Bruggeman, Kirkwood correlation factor and thermodynamic parameters.

Nonvolatile Ferroelectric Memory with Lateral β/α/β In2Se3 Heterojunctions.

The electric dipole locking effect observed in van der Waals (vdW) ferroelectric α-In2Se3 has resulted in a surge of applied research in electronics with nonvolatile functionality. However, ferroelectric tunnel junctions with advantages of lower power consumption and faster writing/reading operations have not been realized in α-In2Se3. Here, we demonstrate the tunneling electroresistance effect in a lateral β/α/β In2Se3 heterojunction built by local laser irradiation. Switchable in-plane polarizations of the vdW ferroelectric control the tunneling conductance of the heterojunction device by 4000% of magnitude. The electronic logic bit can be represented and stored with different orientations of electric dipoles. This prototype enables a new approach to rewritable nonvolatile memory with in-plane ferroelectricity in vdW 2D materials.

Far-field calculation of an arbitrarily oriented electric dipole in horizontal layered confined space

The far-field calculation of arbitrarily oriented electric dipole in a stratified confined space is of great significance in analyzing electromagnetic properties in the lightning return stroke, submarine communication, over-the-horizon ground-wave radar, etc. Based on the mirror image method and the far-field approximation of an electric dipole in free space, a three-layer horizontal confined space model with an arbitrarily oriented dipole is established in this work. Through novel vector operations, the expression of the far field generated by an arbitrarily oriented electric dipole in the confined space model is derived, where the direct wave from the source point to the observation point and the waves reflected by the upper boundary and the lower boundary are all comprehensively considered. On this basis, the radiation characteristics of the electric dipole with frequencies of 100 kHz, 6 MHz and 10 MHz at different positions in the Earth-ionosphere waveguide are compared and analyzed, which are taken for example. Three different orientations of electric dipoles,i.e. vertical direction, horizontal direction, and 45º tilt are taken into account and the corresponding radiation patterns are presented. The results show that the radiation characteristics of electric dipoles in the Earth-ionosphere waveguide will change greatly with their frequencies, orientations and positions. For the electric dipole source at the same location, the higher the frequency, the more the number of radiation lobes is. In addition, when the source frequency keeps unchanged, the farther the dipole source is from the bottom boundary, the more the radiated lobes are. The proposed expression can conveniently and accurately consider the direct wave of a dipole source and its primary reflection from the upper interface and the lower interface in a confined space, and can also be further extended to solving the contribution of multiple reflections from the interfaces.

Molecular interaction studies of isopropyl acetate-xylene mixture using dielectric relaxation approach

Dielectric relaxation parameters of Isopropyl acetate (IPA)-xylene mixtures with different concentrations and temperatures have been measured in the frequency range of 10 MHz to 30 GHz using time domain reflectometry technique. Static dielectric constant, relaxation time, excess permittivity, excess relaxation time, Bruggeman factor, Kirkwood correlation factor and thermodynamic parameters have been determined to understand molecular association between the IPA and xylene molecules. For entire concentrations of IPA-xylene mixture the Kirkwood correlation factor is less than one which shows the antiparallel nature of electric dipole orientation. The experimental values of dielectric constant obtained from time domain reflectometry are in well agreement with theoretical values of dielectric constant obtained by Luzar model. Positive values of enthalpy and entropy indicating that the system is endothermic and less ordered while Gibbs free energy decreases with increase of IPA in xylene.

Improvement of PVDF nanofiltration membrane potential, separation and anti-fouling performance by electret treatment

Electret treatment was a simple method to enhance the charge-electrode properties of polyvinylidene fluoride (PVDF) materials due to the increase of space charge and polarization charge of PVDF materials. The polarization charge was due to the electric dipole orientation change in loose nanofiltration PVDF membrane, which increased the electric dipole moment and improved the polarity of surface potential. Importantly, electret charges were less affected by ambient humidity. Therefore, the electret treatment could improve the surface negative potential of loose nanofiltration PVDF membrane, so as to improve its anti-fouling performance under certain conditions. Based on the above theoretical analysis, the influence and mechanism of the electret treatment on the surface potential, morphology, structure, hydrophilicity and anti-pollution performance of PVDF membrane were studied in this manuscript. When the electret time was 7.5 min and the electret voltage was 30 kV, the surface negative potential was the highest. The content of β phase crystals was 39.1%, which was 12.18% higher than that of untreated membrane. In addition, the surface morphology of PVDF membrane did not change significantly, but the water contact angle decreased slightly, and the pore size increased by 0.36–0.75 nm. Importantly, the flux and the rejection of dye and BSA increased to some extent, and the maximum rejection rate and water flux were increased by 10.34% and 20.25%, respectively. Through the cyclic filtration test and analysis, the anti-fouling performance of membrane was increased due to electrostatic repulsion.

Entanglement dynamics for quantum emitters strongly coupled with molybdenum disulfide nanodisks

We study the dynamics of entanglement for a composite two-qubit system, where each qubit is close to a molybdenum disulfide nanodisk, by combining quantum dynamics and classical electromagnetic calculations. We assume that each qubit interacts locally with its own photonic environment and its free-space decay time is in the picosecond regime. We observe non-Markovian entanglement dynamics indicating strong light-matter interaction between the qubits and the photonic reservoirs. We investigate the entanglement dynamics using entanglement of formation as a measure of entanglement by varying the initial state of the composite system, which always remains an extended Werner-like state, the transition frequency and the orientation of the transition dipole moment of each qubit, the radius of the molybdenum disulfide nanodisk, and the distance of a qubit from its corresponding nanodisk. For several values of the above parameters, we observe interesting phenomena during the time evolution of entanglement of formation, such as entanglement sudden death, revival of entanglement and entanglement trapping. • The entanglement dynamics of two initially entangled quantum emitters next to MoS 2 nanodisks is analyzed. • The results are obtained by combining quantum dynamics calculations with electromagnetic calculations. • Non-Markovian entanglement dynamics is obtained. • Entanglement sudden death, revival of entanglement and entanglement trapping are found for different system parameters. • The effects of the electric dipole orientation of the quantum emitter are also analyzed.

Nonvolatile Ferroelectric Memory Effect in Ultrathin α‐In2Se3

AbstractHigh‐density memory is integral in solid‐state electronics. 2D ferroelectrics offer a new platform for developing ultrathin electronic devices with nonvolatile functionality. Recent experiments on layered α‐In2Se3 confirm its room‐temperature out‐of‐plane ferroelectricity under ambient conditions. Here, a nonvolatile memory effect in a hybrid 2D ferroelectric field‐effect transistor (FeFET) made of ultrathin α‐In2Se3 and graphene is demonstrated. The resistance of the graphene channel in the FeFET is effectively controllable and retentive due to the electrostatic doping, which stems from the electric polarization of the ferroelectric α‐In2Se3. The electronic logic bit can be represented and stored with different orientations of electric dipoles in the top‐gate ferroelectric. The 2D FeFET can be randomly rewritten over more than 105 cycles without losing the nonvolatility. The approach demonstrates a prototype of rewritable nonvolatile memory with ferroelectricity in van der Waals 2D materials.

Aligning in-plane polarization multiplies piezoresponse in P(VDF-TrFE) films on graphite

Ferroelectric polymers are promising as piezoelectric sensors and devices for data storage, energy harvesting and fast energy storage. However, efficient electric polarization as well as piezoelectric and dielectric responses of as-deposited films are often much lower than expected in a crystalline model, because the local orientations of electric dipoles show substantial disorder. Here we introduce an approach for in-plane alignment of the polarization based on applying soft mechanical pressure with a force microscopy tip. Micron-sized ferroelectric domains with well-defined in-plane and out-of-plane polarization orientation and low surface roughness have been written in poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) films on graphite. Inside such domains, the piezoelectric response is more than four times that of the untreated film. The achieved polarization alignment can advance the performance of many devices, since it reduces the cancellation of local responses to electric fields or mechanical strains resulting from polarization disorder.

Complex permittivity spectra of binary polar liquids using time domain reflectometry

The study of complex properties in a binary mixture of polar liquids has been carried out in the frequency range of 10[Formula: see text]MHz to 30 GHz at 293[Formula: see text]K and 298[Formula: see text]K temperatures using time domain reflectometry. The complex properties of polar liquids in binary mixture give information about the frequency dispersion in the dielectric permittivity ([Formula: see text]) and dielectric loss ([Formula: see text]). The information regarding the orientation of electric dipoles in a polar liquid mixture is given by Kirkwood parameters. The Bruggeman parameters are used as the indicator of liquid1 and liquid2 interaction. Molar entropy ([Formula: see text]) and molar enthalpy ([Formula: see text]) are also discussed at the end of the paper.

Dielectric relaxation studies of aqueous solution of polyethylene glycol 200 (PEG200), using time-domain reflectometry

Using time-domain reflectometry measurement technique, the dielectric complex permittivity spectra over the frequency range 10 MHz to 30 GHz have been studied for series of various compositions, at various temperatures, for the aqueous solution of polyethylene glycol 200 (PEG200). The relaxation in these mixtures can be described by a single relaxation time using the Cole–Cole model.[1] The values of static dielectric constant, dielectric relaxation time, excess dielectric permittivity, Bruggeman factor and Kirkwood correlation factor are determined for the series of various compositions. Using above parameters, intermolecular interaction of molecules at molecular level are predicated. The negative values of excess dielectric permittivity suggest reduction in dipole moment, and the values of Kirkwood correlation factor, which are found to be greater than unity, show the parallel orientation of electric dipoles. The study confirms that the intermolecular homogeneous and heterogeneous hydrogen bonding varies significantly with the increase in the concentration of PEG200 in water.

Modifiers of membrane dipole potentials as tools for investigating ion channel formation and functioning.

Electrostatic fields generated on and within biological membranes play a fundamental role in key processes in cell functions. The role of the membrane dipole potential is of particular interest because of its powerful impact on membrane permeability and lipid-protein interactions, including protein insertion, oligomerization, and function. The membrane dipole potential is defined by the orientation of electric dipoles of lipid headgroups, fatty acid carbonyl groups, and membrane-adsorbed water. As a result, the membrane interior is several hundred millivolts more positive than the external aqueous phase. This potential decrease depends on the lipid, and especially sterol, composition of the membrane. The adsorption of certain electroneutral molecules known as dipole modifiers may also lead to significant changes in the magnitude of the potential decrease. These agents are widely used to study the effects of the dipole potential on membrane transport. This review presents a critical analysis of a variety of data from studies dedicated to ion channel formation and functioning in membranes with different dipole potentials. The types of ion channels found in cellular membranes and pores formed by antimicrobial agents and toxins in artificial lipid membranes are summarized. The mechanisms underlying the influence of the membrane dipole potential on ion channel activity, including dipole-dipole and charge-dipole interactions in the pores and in membranes, are discussed. A hypothesis, in which lipid rafts in both model and cellular membranes also modulate ion channel activity by virtue of an increased or decreased dipole potential, is also considered.

External control of the Drosophila melanogaster egg to imago development period by specific combinations of 3D low-frequency electric and magnetic fields

We report that the duration of the egg-to-imago development period of the Drosophila melanogaster, and the imago longevity, are both controllable by combinations of external 3-dimensional (3D) low-frequency electric and magnetic fields (LFEMFs). Both these periods may be reduced or increased by applying an appropriate configuration of external 3D LFEMFs. We report that the longevity of D. melanogaster imagoes correlates with the duration of the egg-to-imago development period of the respective eggs. We infer that metabolic processes in both eggs and imago are either accelerated (resulting in reduced time periods) or slowed down (resulting in increased time periods). We propose that external 3D LFEMFs induce electric currents in live systems as well as mechanical vibrations on sub-cell, whole-cell and cell-group levels. These external fields induce media polarization due to ionic motion and orientation of electric dipoles that could moderate the observed effects. We found that the longevity of D. melanogaster imagoes is affected by action of 3D LFEMFs on the respective eggs in the embryonic development period (EDP). We interpret this effect as resulting from changes in the regulation mechanism of metabolic processes in D. melanogaster eggs, inherited by the resulting imagoes. We also tested separate effects of either 3D electric or 3D magnetic fields, which were significantly weaker.

An orbital-overlap model for minimal work functions of cesiated metal surfaces

We introduce a model for the effect of cesium adsorbates on the work function of transition metal surfaces. The model builds on the classical point-dipole equation by adding exponential terms that characterize the degree of orbital overlap between the 6s states of neighboring cesium adsorbates and its effect on the strength and orientation of electric dipoles along the adsorbate–substrate interface. The new model improves upon earlier models in terms of agreement with the work function–coverage curves obtained via first-principles calculations based on density functional theory. All the cesiated metal surfaces have optimal coverages between 0.6 and 0.8 monolayers, in accordance with experimental data. Of all the cesiated metal surfaces that we have considered, tungsten has the lowest minimum work function, also in accordance with experiments.

Orientation of the HAARP ELF ionospheric dipole and the auroral electrojet

The HF heating facility of the High Frequency Active Auroral Research Program (HAARP), located near Gakona, Alaska, generates ELF (300 Hz ‐ 3 kHz) waves via modulated HF (2.7–10 MHz) heating of the auroral electrojet. Using two ELF/VLF receivers at ∼700 km from HAARP, the orientation of the equivalent ELF radiating ionospheric dipole is inferred from the relative strength and Earth‐ionosphere waveguide modal content of signals received. In several cases analyzed the effective HAARP electric dipole orientation is generally along magnetic east‐west direction. A new metric is introduced to evaluate the validity of the determination of source characteristics with medium and long‐range ELF/VLF measurements. Results are put into context of the auroral electrojet, indicating the possibility of studying small‐scale electrojet structure not observable with magnetometers.

Mixed systems of ferroelectric relaxors

The random field based model for calculation of mixed systems of ferroelectric relaxors is proposed. Different orientations of electric dipoles related to different solid solution components and contribution of random field nonlinear and correlation effects were taken into account. Calculations of transition temperature Tc and order parameters concentrational and temperature dependence were performed. The integral equations for these quantities calculation were derived. The theory was applied for description of mixed (PSN)1−x (PST)x with different degree of order and (PMN)1−x(PST)x systems. The higher Tc value for more disordered (PSN)1−X(PST)x system in the region 0 ≤ x < 0,5 was shown to be related to larger nonlinearity coefficient of PSN in comparison with PST. Temperature dependent concentration of morphotropic region existence was obtained in (PMN)1−x(PT)x. Numerical calculations with the fitting parameters derived mainly from Tc values of solid solution components describes pretty good observed phase diagram of both aforementioned mixed systems of ferroelectric relaxors.

Dielectric Relaxation of H-Bonded Liquids. Mixtures of Ethanol and n-Hexanol at Different Compositions and Temperatures

At different temperatures T (0 °C ≤ T ≤ 60 °C) and mole fractions x of ethanol (0 ≤ x ≤ 1) the complex (electric) permittivity of ethanol/n-hexanol mixtures has been measured as a function of frequency ν between 1 MHz and 18 GHz. Within this frequency range of measurement the dielectric spectra reveal two relaxation regions. The relaxation time of the dominating relaxation process varies between τ1 = 63 ps (x = 1; 60 °C) and τ1 = 2.8 ns (x = 0; 0 °C). The relaxation time τ2 of the second process is smaller (5 ps ≤ τ2 ≤ 109 ps). The extrapolated static permittivity ε(0) of the alcohol systems is evaluated to show that there is a noticeable effect of permanent electric dipole orientation correlation. The relaxation terms are discussed in the light of hydrogen bond fluctuations and modes of reorientational motions of alcohol molecules. A remarkable result is the finding that the activation enthalpy associated with the dominating relaxation process can be represented by a sum of contributions from interactions between the hydrogen bonding OH-groups and between the methylene as well as methyl groups of the alcohol molecules. This finding suggests intermolecular interactions between the aliphatic groups to play a siginificant role in the dynamics of the molecular reorientations.

Effect of poling temperature on optical second harmonic intensity of sodium zinc tellurite glasses

Poling temperature dependence of optical second harmonic intensity has been examined for Na2O–ZnO–TeO2 glasses. All the glasses exhibit such a tendency that the second harmonic intensity increases, experiences a maximum, and decreases as the poling temperature increases. The poling temperature giving rise to the maximum second harmonic intensity, which we call an optimum poling temperature, correlates with glass transition temperature; there exists a linear relation between them. This phenomenon indicates that the structural change of glass network near the glass transition temperature affects the orientation of electric dipoles with a long range order which induces the second harmonic generation. We suggest that some electrochemical reactions take place on the anode-side surface of glass at around the glass transition temperature where viscous flow is allowed and disturb the orientation of electric dipoles.