Square Of Electric Field Research Articles

Anisotropic linear and nonlinear charge-spin conversion in topological semimetal SrIrO3

Over the past decade, utilizing spin currents in the linear response of electric field to manipulate magnetization states via spin-orbit torques (SOTs) is one of the core concepts for realizing a multitude of spintronic devices. Besides the linear regime, recently, nonlinear charge-spin conversion under the square of electric field has been recognized in a wide variety of materials with nontrivial spin textures, opening an emerging field of nonlinear spintronics. Here, we report the investigation of both linear and nonlinear charge-spin conversion in one single topological semimetal ${\mathrm{SrIrO}}_{3}(110)$ thin film that hosts strong spin-orbit coupling and nontrivial spin textures in the momentum space. In the nonlinear regime, the observation of crystalline direction dependent response indicates the presence of anisotropic surface states induced spin-momentum locking near the Fermi level. Such anisotropic spin textures also give rise to spin currents in the linear response regime, which mainly contributes to the fieldlike SOT component. Our work demonstrates the power of combination of linear and nonlinear approaches in understanding and utilizing charge-spin conversion in topological materials.

Evaluation of Isomotive Insulator-Based Dielectrophoretic Device by Measuring the Particle Velocity.

Many dielectrophoretic (DEP) devices for biomedical application have been suggested, such as the separation, concentration, and detection of biological cells or molecules. Most of these devices utilize the difference in their DEP properties. However, single-cell analysis is required to evaluate individual properties. Therefore, this paper proposed a modified isomotive insulator-based DEP (iDEP) creek-gap device for straightforward single-cell analysis, which is capable of measurement at a wide frequency band. The proposed iDEP device generates more constant particle velocity than the previous study. The insulator was fabricated using backside exposure for accurate forming. We measured the distribution of the particle velocity and frequency property, using homogeneous polystyrene particles to verify the effectiveness of the proposed device. The results show that the particle velocity distribution was consistent with the distribution of the numerically calculated electric field square (). Furthermore, the velocity measurement, at a wide frequency band, from 10 Hz to 20 MHz, was performed because of the long distance between electrodes. These results suggest that the prop-erties of various particles or cells can be obtained by simple measurement using the proposed device.

Numerical simulation of the electric field induced in a contactless dielectrophoretic quadrupole cell separator

PurposeThis study aims to propose a contactless and continuous dielectrophoretic cell-separation device using quadrupole electric field. To examine the separation performance, numerical simulations of the electric field in the cross-section of the glass capillary installed in the center of the quadrupole electrode were conducted.Design/methodology/approachTo estimate the magnitude of the dielectrophoretic force induced on cells, electrostatic analysis was performed by using a boundary-fitted coordinate system.Distribution of the electric field and gradient of the electric field square in the cross-section of the glass capillary were simulated for various ratios of radii of the glass capillary to the electrode rod.FindingsThe distribution of the electric field was found to have a cone-like profile about the center axis of the glass capillary with maximum at the internal surface of the glass capillary. The magnitude of the gradient of electric field square had similar distribution as that of the electric field, but had steeper slope near the internal surface of the glass capillary. The optimal values of the ratio of radii and the applied voltage were also estimated to achieve the local electric field strength suitable for cell separation.Originality/valueOne major advantage of the proposed device is simple and low fabrication cost, in addition to its contactless structure free from cell damage. Derived knowledge is instructive in achieving high-throughput cell separation without the use of devices of complex structure.

Vector properties of a circular plate diffracted by the plane wave with sub-wavelength size

The vector diffraction of linearly polarized plane wave passing through a thin circular plate with a sub-wavelength radius is investigated by the finite element method. The transverse distribution and propagating evolution of the diffracted field with different intensity expressions are analyzed and compared. It shows that there are not only the component of the incident polarization, but also those of other two vertical directions in the near-field diffracted region. Regardless of the relationship between the wavelength and the radius of the circular plate, the diffracted field could evolve into a steady annular diffracted pattern, in which there is a central bright spot (so-called Poisson spot). There is an obvious difference of the diffracted properties between two intensity expressions from the square of electric field and the average magnitude of the Poynting vector as the propagation distance is very small, while they can be considered same with a large propagation distance (e.g. more than a wavelength).

Enhancement of the local asymmetry in the hydrogen bond network of liquid water by an ultrafast electric field pulse

Condensed phase electron decomposition analysis based on density functional theory has recently revealed an asymmetry in the hydrogen-bond network in liquid water, in the sense that a significant population of water molecules are simultaneously donating and accepting one strong hydrogen-bond and another substantially weaker one. Here we investigate this asymmetry, as well as broader structural and energetic features of water’s hydrogen-bond network, following the application of an intense electric field square pulse that invokes the ultrafast reorientation of water molecules. We find that the necessary field-strength required to invoke an ultrafast alignment in a picosecond time window is on the order of 108 Vm−1. The resulting orientational anisotropy imposes an experimentally measurable signature on the structure and dynamics of the hydrogen-bond network, including its asymmetry, which is strongly enhanced. The dependence of the molecular reorientation dynamics on the field-strength can be understood by relating the magnitude of the water dipole–field interaction to the rotational kinetic energy, as well as the hydrogen-bond energy.

Omnidirectional infrared nonreciprocal absorbers based on CdTe gratings

In this paper, a novel CdTe gratings structure is designed aimed at constructing omnidirectional infrared nonreciprocal absorbers at wavelength from 18 μm to 23 μm. CdTe is a commonly used semiconductor infrared film material, which is widely used in photovoltaic, infrared detection, fluorescence and other applications. The optical radiation characteristics of magneto-optical material CdTe are studied based on the Lorentz-Drude model, which is verified with the optical constants in handbook. The time-domain finite difference (FDTD) method was used to calculate the infrared radiation characteristics of CdTe gratings, and the electric field square modulus distribution with different wavelengths is presented. It is found that the nonreciprocal absorptivity is obvious as the incidence angle is 45° at the positive and negative angles. The effects of magnetic field strength, grating thickness, incidence angles on the optical properties, especially the non-reciprocity are analyzed in details. The numerical simulation results are useful to the thermal radiative design in infrared absorber and other optical instrument.

Analysis of the dielectrophoretic properties of cells using the isomotive AC electric field.

Various microfluidic devices utilizing the principle of dielectrophoresis (DEP) have been developed to separate, concentrate, and characterize biological cells; however, their performance is still limited by a lack of quantitative characterization. We addressed this limitation by employing a method capable of accurately quantifying a cell's response to an imposed field gradient. In this study, a simple method using a newly designed Creek-gap electrode was proposed, and the electrokinetic behavior of cells was characterized by DEP velocimetry under the exposure of an approximately constant gradient of electric field square established along the gap of the electrodes. Together with the numerical prediction of the electric field based on three-dimensional electric field analysis, the magnitude of DEP forces and the real part of the Clausius-Mossotti factor of cells were deduced from their movement. Results demonstrated that the proposed method was applicable to the determination of the dielectrophoretic properties of cells.

Ultrathin nanoporous membranes for insulator-based dielectrophoresis

Insulator-based dielectrophoresis (iDEP) is a simple, scalable mechanism that can be used for directly manipulating particle trajectories in pore-based filtration and separation processes. However, iDEP manipulation of nanoparticles presents unique challenges as the dielectrophoretic force exerted on the nanoparticles can easily be overshadowed by opposing kinetic forces. In this study, a molecularly thin, SiN-based nanoporous membrane (NPN) is explored as a breakthrough technology that enhances By numerically assessing the gradient of the electric field square —a common measure for magnitude—it was found that the unique geometrical features of NPN (pore tapering, sharp pore corner and ultrathin thickness) act in favor of intensifying the overall A comparative study indicated that generated in NPN are four orders of magnitude larger than track-etched polycarbonate membranes with comparable pore size. The stronger suggests that iDEP can be conducted under lower voltage bias with NPN: reducing joule heating concerns and enabling solutions to have higher ionic strength. Enabling higher ionic strength solutions may also extend the opportunities of iDEP applications under physiologically relevant conditions. This study also highlights the effects of induced by the ion accumulation along charged surfaces (electric-double layer (EDL)). EDL-based exists along the entire charged surface, including locations where geometry-based iDEP is negligible. The high surface-to-volume ratio of NPN offers a unique platform for exploiting such EDL-based DEP systems. The EDL-based was also found to offset the geometry-based but this effect was easily circumvented by reducing the EDL thickness (e.g. increasing the ionic strength from 0.1 to 100 mM). The results from this study imply the potential application of iDEP as a direct, in-operando antifouling mechanism for ultrafiltration technology, and also as an active tuning mechanism to control the cut-off size limit for continuous selectivity of nanomembrane-based separations.

Electric field in an AC dielectric barrier discharge overlapped with a nanosecond pulse discharge

The effect of ns discharge pulses on the AC barrier discharge in hydrogen in plane-to-plane geometry is studied using time-resolved measurements of the electric field in the plasma. The AC discharge was operated at a pressure of 300 Torr at frequencies of 500 and 1750 Hz, with ns pulses generated when the AC voltage was near zero. The electric field vector is measured by ps four-wave mixing technique, which generates coherent IR signal proportional to the square of electric field. Absolute calibration was done using an electrostatic (sub-breakdown) field applied to the discharge electrodes, when no plasma was generated. The results are compared with one-dimensional kinetic modeling of the AC discharge and the nanosecond pulse discharge, predicting behavior of both individual micro-discharges and their cumulative effect on the electric field distribution in the electrode gap, using stochastic averaging based on the experimental micro-discharge temporal probability distribution during the AC period. Time evolution of the electric field in the AC discharge without ns pulses, controlled by a superposition of random micro-discharges, exhibits a nearly ‘flat top’ distribution with the maximum near breakdown threshold, reproduced quite well by kinetic modeling. Adding ns pulse discharges on top of the AC voltage waveform changes the AC discharge behavior in a dramatic way, inducing transition from random micro-discharges to a more regular, near-1D discharge. In this case, reproducible volumetric AC breakdown is produced at a well-defined moment after each ns pulse discharge. During the reproducible AC breakdown, the electric field in the plasma exhibits a sudden drop, which coincides in time with a well-defined current pulse. This trend is also predicted by the kinetic model. Analysis of kinetic modeling predictions shows that this effect is caused by large-volume ionization and neutralization of surface charges on the dielectrics by ns discharge pulses. The present work demonstrates that this effect may be used to control the phase of AC barrier discharges, triggering reproducible breakdowns at well-defined moments.

Fabrication, electrical characterization, and detection application of graphene-sheet-based electrical circuits

The distribution of potential, electric field, and gradient of square of electric field was simulated via a finite element method for dielectrophoresis (DEP) assembly. Then reduced graphene oxide sheets (RGOS)- and graphene oxide sheets (GOS)-based electrical circuits were fabricated via DEP assembly. The mechanically exfoliated graphene sheets (MEGS)-based electrical circuit was also fabricated for comparison. The electrical transport properties of three types of graphene-based electrical circuits were measured. The MEGS-based electrical circuit possesses the best electrical conductivity, and the GOS-based electrical circuit has the poorest electrical conductivity among all three circuits. The three types of electrical circuits were applied for the detection of copper ions (Cu2+). The RGOS-based electrical circuit can detect the Cu2+ when the concentration of Cu2+ was as low as 10 nM in solution. The GOS-based electrical circuit can only detect Cu2+ after chemical reduction. The possible mechanism of electron transfer was proposed for the detection. The facile fabrication method and excellent performance imply the RGOS-based electrical circuit has great potential to be applied to metal ion sensors.

NUMERICAL STUDY OF DIELECTROPHORESIS FORCE IN THE ISOLATED ELECTRODE: A COMPARATIVE APPROACH

One of the general methods for particle separation in lab-on-a-chips (LOCs) is dielectrophoresis (DEP). The effects of electrode isolation in DEP-based particle separation devices are discussed throughout this paper. One advantage of the electrode isolation is reducing electrode–electrolyte–sample mutual interactions. In this study, the conventional DEP forces using interdigitated electrode arrays is numerically investigated without and in the presence dielectric layer in the interface of electrode and electrolytic fluid. The study includes the effect of dielectric layer thickness when fluids of different electrical conductivity are involved. The results show that the electric field and also intra-channel gradient of electric field square depend on frequency and an isolating layer acts as high-pass filter, thus frequency response of conventional DEP force besides Clausius–Mossotti (CM) factor is depended on the electric field gradient. The results also show that in contactless model, the frequency response of the DEP forces can be engineered by dielectric thickness and electrical conductivity of the suspending medium. According to the obtained results, during particle separation with DEP method in the presence of insolated electrodes and considering the reduction in electric field intensity, an appropriate and optimal choice for working frequency, voltage of electrodes and thickness of dielectric layer should be considered. The particles and dielectric isolated layer under study is polystyrene beads and polydimethylsiloxane (PDMS) elastomeric polymer, respectively.

Pulsating emission of droplets from an electrified meniscus

A numerical description is given for the pulsating emission of droplets from an electrified meniscus of an inviscid liquid of infinite electrical conductivity which is injected at a constant flow rate into a region of uniform, continuous or time periodic, electric field. Under a continuous field, the meniscus attains a periodic regime in which bursts of tiny droplets are emitted from its tip. At low electric fields this regime consists of sequences of emission bursts interspersed with sequences of meniscus oscillations without droplet emission, while at higher fields the bursts occur periodically. These results are in qualitative agreement with experimental results in the literature. Under a time periodic electric field with square waveform, the electric stress that acts on the surface of the liquid while the field is on may generate a tip that emits tiny droplets or may accelerate part of the meniscus and lead to a second emission mode in which a few large droplets are emitted after the electric field is turned off. Conditions under which each emission mode or a combination of the two are realized are discussed for low frequency oscillatory fields. A simplified model is proposed for high electric field frequencies, of the order of the capillary frequency of the meniscus. This model allows computing the average emission rate as a function of the amplitude, duration and bias of the electric field square wave, and shows that droplet emission fails to follow the applied field above a certain frequency.

Orientational Kerr effect and phase modulation of light in deformed-helix ferroelectric liquid crystals with subwavelength pitch

We study both theoretically and experimentally the electro-optical properties of vertically aligned deformed helix ferroelectric liquid crystals (VADHFLC) with subwavelength pitch that are governed by the electrically induced optical biaxiality of the smectic helical structure. The key theoretical result is that the principal refractive indices of homogenized VADHFLC cells exhibit the quadratic nonlinearity and such behavior might be interpreted as an orientational Kerr effect caused by the electric-field-induced orientational distortions of the FLC helix. In our experiments, it has been observed that, for sufficiently weak electric fields, the magnitude of biaxiality is proportional to the square of electric field in good agreement with our theoretical results for the effective dielectric tensor of VADHFLCs. Under certain conditions, the 2π phase modulation of light, which is caused by one of the induced refractive indices, is observed without changes in ellipticity of incident light.

Electro-Optic Coefficient r51 of LiNbO3 Crystal Obtained from Measurement of Retardation Induced by Square of Electric Field

A versatile method of measuring electro-optic coefficients (rij: i=4–6 and j=1–3) of isometric, uniaxial, and biaxial crystals without crystal coordinate rotation has been developed. It has been confirmed theoretically and experimentally that the change in the retardation of an X-cut Y-propagation LiNbO3 crystal depends on the square of the electric field along the X-direction. The constant stress electro-optic coefficient r51 of the LiNbO3 crystal is found to be 32.05±0.01 pm/V at 632.8 nm.

Surface Potential Equation for Metal-Oxide-Semiconductor Capacitors Considering the Degenerate Effect

A surface potential equation (SPE) considering the degenerate effect is derived. To make the degenerate SPE analysis, an empirical approximation for the Fermi integral is applied in the derivation. Dependences of surface potential and square of electric field on gate voltage calculated from the degenerate and non-degenerate models are compared with great discrepancy. Further, theoretical C—V relationships are compared with the experimental data for two structures and it is shown that the degenerate SPE-based Cg—Vg matches with the experimental data much better than the non-degenerate one, which confirms that the degenerate effect is inevitable for surface potential-based metal-oxide-semiconductor device modeling.

Improvement of Microchannel Geometry Subject to Lateral Dielectrophoresis Using Numerical Simulations

Continuous particles separation device by lateral dielectrophoretic force shows a favorable promise for multiple cell population separation and purification. This paper addresses the effects of micro-channel geometry shape on the electric field distribution and the distribution of the gradient of electric field square which has a direct influence on the magnitude of the dielectrophoretic force. Before this was done, the influence of aspect ratio of micro-channel geometry was investigated first. Numerical method was adopted in this paper to study the electric field distribution and the gradient of the electric field square distribution. Results show that micro-channel geometry shape and its aspect ratio have great influence on the electric field distribution and dielectrophoresis distribution. As a result, this paper proposes novel micro-channel geometry to improve electric field distribution, further more for a better dielectrophoresis separation. The improved micro-channel can generate stronger electric field strength and larger dielectrophoretic force.

Sheath structure in front of an electron emitting electrode immersed in a two-electron temperature plasma: a fluid model and numerical solutions of the Poisson equation

A one-dimensional fluid model of sheath formation in front of a large, planar, floating, electron emitting electrode (collector) immersed in a two-electron temperature plasma is presented. For certain values of the parameters the Bohm criterion is triple valued. Three methods to select the correct Bohm velocity are compared. The simplest is to find the parameters, where the floating potentials that correspond to the high and to the low Bohm velocity are equal. But sometimes—when the electron emission is small—such parameters cannot be found. The second method is the ‘maximum positive ion flux criterion’, proposed recently by Fernández Palop et al (2002 J. Appl. Phys. 91 2587), for electronegative plasmas. In this work it is modified for a two-electron temperature plasma with emitted electrons and applied successfully. This method is sometimes—when the electron emission from the collector is increased—not applicable because the positive ion flux as a function of potential has only 1 maximum. The third method is a numerical solution of the Poisson equation. The transition from the low to the high Bohm velocity occurs at the parameters where the numerically found space charge density profile indicates the formation of a double layer in the sheath. These parameters are always identical to the parameters found with the maximum positive ion flux method, when the latter can be applied. The ‘shooting method’ for the correct determination of electric field at the collector is presented. This method reveals the existence of regular and irregular numerical solutions of the Poisson equation. The irregular solutions of the Poisson equation fulfill only one of the two sheath edge conditions and they correspond to the solutions of the fluid model, that are not physically acceptable. The parameters, where the numerical solutions of the Poisson equation become irregular, are identical to those found with the ‘positive square of electric field’ test, which is also presented.

Time-resolved diffraction measurements of electric-field-induced strain in tetragonal lead zirconate titanate

The dynamic electric-field-induced strain in piezoelectric ceramics enables their use in a broad range of sensor, actuator, and electronic devices. In piezoelectric ceramics which are also ferroelectric, this macroscopic strain is comprised of both intrinsic (piezoelectric) and extrinsic (non-180° domain switching) strain components. Extrinsic contributions are accompanied by hysteresis, nonlinearity, and fatigue. Though technologically significant, direct measurement of these mechanisms and their relative contributions to the macroscopic response has not yet been achieved at driving frequencies of interest. Here we report measurements of these mechanisms in ceramic lead zirconate titanate during application of subcoercive cyclic driving electric fields using an in-situ stroboscopic neutron diffraction technique. Calculations are made from the diffraction measurements to determine the relative contributions of these different strain mechanisms. During applied electric field square waves of +0.5Ec unipolar and ±0.5Ec bipolar, at 1 Hz, non-180° domain switching is found to contribute 34% and 40% of the macroscopically measured strain, respectively.

Properties of Oligo-polyphenylene Molecular Wires under External Electric Field

Theoretical investigations of conducting molecular wire of oligo-polyphenylene molecules under external electronic field were carried out using ab initio Hartree-Fock method with 6-31G* basis set. The electric field dependence of the molecular geometry, electronic structure, the spatial distribution, and the energy level of the frontier orbitals of the molecular wire was revealed. The torsion angle deviation was a function of square of electric field. When the external electric field increased, the torsion angles became smaller, the single bonds became shorter, and the molecular configuration tended to be more planar. All these features made the molecular wire more conjugated. The molecular electronic structure was sensitive to the electric field as well. With increasing electric field, the HOMO-LUMO gap decreased. Moreover, the spatial distribution of LUMO moved to the high potential end, whereas HOMO to the low potential end. Furthermore, the polyphenylene (PP) molecule with sulfur atoms bridged between two gold electrodes was studied by non-equilibrium Green′s function formalism to further understand the electron transport of molecular wire under external electric field.

Optical performance and laser induced damage threshold improvement of diffraction gratings used as compressors in ultra high intensity lasers

This paper studies gratings engraved in a multilayer dielectric stack for ultra high intensity laser compressors. A metal layer is inserted between the substrate and the dielectric stack to reduce the number of dielectric bilayers and thus the mechanical stress within the stack. A code taking account the fluctuation range of the geometrical parameters during the fabrication process is used to numerically optimize the mirror stack and study different groove profiles to increase the reflected efficiency and the laser induced damage threshold. It is evidenced that of all the profiles leading to good diffraction performances, those with the greatest groove depth and width values result in the smallest enhancement of the electric field square inside the grating with a decrease by a factor close to 2.5.