Application Of Static Electric Field Research Articles

Removing the orientational degeneracy of the TS defect in 4H–SiC by electric fields and strain

We present a photoluminescence (PL) study of the recently discovered TS defect in 4H silicon carbide. It investigates the influence of static electric fields and local strain on the spectral properties by means of low temperature (≈4 K) ensemble measurements. Upon application of static electric fields exerted by graphene electrodes, line splitting patterns are observed, which are investigated for four different angles of the electric field with respect to the principal crystallographic axes. More detailed information can be gained when additionally the excitation polarization angle is systematically varied. Altogether, the data allow for extracting the direction of the associated electric dipole moments, revealing three distinct orientations of the underlying TS defect inside the crystal’s basal plane. We also present three so far unreported PL lines (836.7 nm, 889.7 nm, 950.0 nm) as candidates for out-of-plane oriented counterparts of the TS lines. Similar to symmetry breaking by the electric field applied, strain can reduce the local symmetry. We investigate strain-induced line splitting patterns that also yield a threefold directedness of the TS lines in accordance with the Stark effect measurements. The response to both electrical and strain fields is remarkably strong, leading to line shifts of ±12 meV of the TS1 line. Combining our findings, we can narrow down possible geometries of the TS defect.

Effects of trifluoromethyl substituents on interfacial and bulk polarization of polystyrene gate dielectrics

The ability to control the bulk and interfacial polarization of dielectric polymers is important to their application in organic electronics. We examine the effect of the trifluoromethyl substituent on poly(3-trifluoromethylstyrene) (P3TFMS) as compared to unsubstituted polystyrene (PS) on the I-V relationships of pentacene-based organic field-effect transistors (OFETs). Single- and double-layered films of these polymers were used, with lower layers crosslinked through vinylbenzocyclobutene comonomers before deposition of upper layers. Control experiments verified that the electronic effect of the crosslinking was negligible. We found that the TFM substituent markedly and independently affected both the initial threshold voltage Vth and the nonvolatile, shifted Vth observed after the application of static gate voltage, depending on its position adjacent or apart from the pentacene. The trifluoromethyl-bearing polymers exhibited significantly lower magnitude initial threshold voltages (Vth,i of ca. −17 V for P3TFMS compared to −35 V for PS), large threshold voltage shifts after charging by the application of static electric fields (ΔVth of ca. 32 V for P3TFMS and 17 V for PS), and greater stability of the ΔVth under repeated charge/discharge cycles. These results are consistent with P3TFMS having fewer interfacial trap states but more stable bulk trap states. The results are applicable to organo-electronic systems such as piezoelectrics for energy harvesting and nonvolatile OFETs such as memory, sensing, and logic elements.

A review on effect of DC voltage on crystallization process in food systems

Abstract Crystallization of water and food systems may be affected by electric and magnetic fields. In this review paper, the crystallization of water and food systems assisted by DC voltage (DC-V) is compiled based on existing literature. Two ways of applying DC-V during electrocrystallization can be identified, namely charge flow (CF) conditions with electrical charges flowing through the matrix and static electric field (SEF) conditions. Both processes have shown to interact with nucleation mechanism by reducing supercooling and favouring a higher nucleation rate. The theoretical calculations show that the application of SEF can modify the free energy of formation of ice nuclei in the water phase. Moreover, SEF application can also enhance heat and mass transfer during crystallization process. Various molecular simulations and experimental studies have shown that SEF aligns the water molecules in its direction by the phenomenon of dielectric polarization, and thus, reduces the degree of supercooling (∆T). The freezing process under SEF produces smaller ice crystals in the food products, resulting in less freeze damage; it is thus expected to minimize cell disruption, to reduce the drip loss, to lessen the protein denaturation, and finally to preserve the texture of the fresh food after thawing. Furthermore, freezing under SEF may help to use less energy intensive freezing conditions (higher set point temperature, low air velocity). As a conclusion, the use of DC-V in the case of crystallization of food systems (especially freezing) offers a new perspective to the food industry.

All-optical injection of charge, spin, and valley currents in monolayer transition-metal dichalcogenides

Monolayer transition metal dichalcogenides have recently become a playground for spin- and valleytronics research. Their low energy spectrum can be described by Dirac cones on the corners of Brillouin zone, but the physical properties are richer than those of graphene since the spin degeneracy is lifted and the optical selection rules are valley dependent. This has been exploited for the optical injection of spin and valley polarized currents by the application of static electric fields. In this paper we consider an all-optical method for the injection of charge, spin and valley polarized currents. The presence of both a fundamental optical field and its second harmonic can lead to the injection of currents due to a nonlinear effect involving the quantum interference between one- and two-photon absorption processes. We analyze how the injected quantities can be controlled through the parameters of the incident light fields, allowing capabilities of control beyond those achieved with static fields, and discuss the conditions for experimental verification of our results.

Role of internal field and exhaustion in ferroelectric switching

The role of internal field and exhaustion during ferroelectric switching was investigated by studying the dynamics of polarisation switching during the application of static electric fields at different points of the polarization-electric field (P-E) loop of a ferroelectric ceramic (PZT 5A). By simultaneously measuring polarization and strain changes during creep an insight into the evolution of the internal field during polarization switching was obtained. Electric field partial unloading tests were performed to estimate the magnitude of the effective internal field at different points of the P-E loop. Results show that the internal field increases proportionally with polarization reversal. A rate model that includes the effect of thermal fluctuations, internal field and exhaustion of nucleation sites during switching has been developed and applied to fit the polarization creep curves. The fitting of the creep curves in the sub-coercive region suggests that polarization hardening (increasing of internal field) is the mechanism controlling the polarization rate decay. At higher static applied electric fields the mechanism gradually changes and the exhaustion of the available nucleation sites becomes the main process responsible for the creep rate decay.

Measurement of Structural Changes in Tetragonal PZT Ceramics under Static and Cyclic Electric Fields Using a Laboratory X-ray Diffractometer

In situ structural characterization techniques that are capable of characterizing piezoelectric ceramics under different electrical loading conditions are important to understand the behavior of materials during their use. In this work, we report the use of a laboratory X-ray diffractometer for the measurement of various structural changes in tetragonal La-doped lead zirconate titanate (PZT) ceramics under the application of static and cyclic electric fields. The changes in the volume fractions of the 90 degrees domains parallel to the electric field direction are calculated from the intensities of the {002} diffraction peaks. In addition, the components of lattice strains are monitored from the changes in the (111) crystallographic planes. It is observed that, under the application of static electric fields, both 90 degrees domain switching and the 111 lattice strains showed similarity with the macroscopic strain-electric field hystersis loop. To measure the structural changes under cyclic electric fields, a time-resolved X-ray diffraction technique was used. Under application of a square-wave electric field of amplitude +/-650 V/mm and frequency 0.3 Hz, a change of approximately 5% in the volume fraction of the 90 degrees domains and approximately 0.07% strain of the 111 lattice planes are observed. Both the amount of 90 degrees domain switching and the 111 lattice strains are observed to increase with an increase in the amplitude of the cyclic electric field. The implications of the measured structural changes for the macroscopic piezoelectric properties of ceramics are discussed.

Quadrupolar Chromophores for Voltage Sensing and White‐Light Generation

A few-state model predicts that spectral properties of some quadrupolar chromophores are affected by the application of static electric fields. These dyes can monitor neuronal activity (action potential), as a sensitive and versatile alternative to classical dipolar dyes and can also be used in organic LEDs: color-tunable and/or white-light emission is obtained by varying the working voltage (see chromaticity diagram).

Quantum dynamics of relaxation of a pair of coupled Morse oscillators: Effects of mass and electrical asymmetries

AbstractA multiconfiguration time‐dependent Hartree method based recipe is used to study the role of mass and electrical asymmetry in controlling the quantum dynamics of relaxation of a locally excited OH bond in a water molecule, modeled by a pair of interacting Morse oscillators. The fast periodic energy transfer between the two equivalent OH bonds in HOH is replaced by a rather slow process when one of the H atom is replaced by a deuterium atom. Application of static electric field along the OD bond in HOD molecule is seen to either enhance or damp the relaxation rate, depending on the strength of the applied field. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Integrated micromachined components for biological analysis systems

In this paper, we provide an overview of miniaturized biochemical analysis system components and specifically discuss the micromachined metallic pipette arrays (MPA) and the micromachined electrical field-flow fractionation system (μ-EFFF). The MPA are arrays of hollow metallic pipettes extending from a silicon substrate. These arrays are used in macroscale spatial manipulation of samples in the pl to μl range. The μ-EFFF system is composed of a micromachined flow channel with integrated electrodes for application of static electric fields. The system is used for separation and analysis of biological molecules and colloids. The design, fabrication, and characterization of the MPA and the μ-EFFF are described. In addition, the integration of the components using micromechatronics technologies is discussed.

Dynamic Studies of Transport Properties of γ-Mo4O11Crystals Using Photoinduced Transient Thermoelectric Effect under Static Electric Field

The pulsed-laser induced \lq\lqtransient thermoelectric effect (TTE) \rq\rqof a quasi-two-dimensional γ-Mo 4 O 11 crystal has been measured under a static electric field over the time range 50 ns–100 ms and temperature range 6–300 K. Upon application of static electric field, the TTE voltages are enhanced and most of these signals change their sign for reversal of the field direction, which is attributable to the change in photoinduced \lqambipolar states'. The TTE voltages are characterized by photo-generated carrier diffusions with four relaxation times τ i ( i =1-4), from which we have evaluated the carrier mobilities µ i . Using our dynamic data and existing block-band model, we have self-consistently calculated the temperature dependence of the dc transport quantities, in satisfactory agreement with the experiments. The difference in the electronic properties for γ - and its similar η -type Mo 4 O 11 is also discussed.

The effect of alkali ion migration on the adhesion of sputtered chromium metallizations to glass

Alkali ion migration has been identified as a mechanism for the loss of adhesion of magnetron sputtered, chromium metallizations to glass. The onset of this mechanism of adhesion loss has been correlated with the power dissipated during the magnetron sputter deposition. It is proposed that the combination of substrate heating and electric fields produced during magnetron sputter deposition leads to alkali–ion migration to the chromium–glass interface, which affects the film adhesion. The concentration of alkali at the interface was measured by x-ray photoelectron spectroscopy. It was found that for 7740 Pyrex glass, the concentration of sodium at the interface was greatly increased over that at the substrate surface prior to sputter deposition. As a further test of this mechanism of adhesion loss, the adhesion of chromium films to glass was modified by the application of static electric fields to heated sputter coated specimens. Again, sodium was found to accumulate at the interface of poorly adhering films.

Effect of Electric Field on the IC-C Phase Transition in K2SeO4

The effect of electric field on the IC-C phase transition in K2SeO4 has been investigated by measuring the ESR spectra and the crystal current in the ESR circuit. It has been found that time development of the crystal current after the application of static electric field shows two different time dependencies; one is rapid and reversible and the other is slow and irreversible. The slow change of the crystal current can be represented well as t0.21. The peak of the crystal current which corresponds to that of the dielectric loss shifts to higher temperature with increase of the frequency of applied microwave. From the quantitative analysis of the shift, it is shown that the polarization fluctuation around Tc in K2SeO4 can be explained by the relaxational model with a temperature dependent activation potential.

Effect of hot electrons on microwave and submillimeter wave transmission through an InSb slab in the Faraday configuration

The variation of the attenuation rates of the circularly polarized waves and the slab transmittance with the hot carrier temperature ${T}_{e}$ are investigated with the aid of a high-field mobility model in which ${E}_{0}$ and the carrier drift velocity ${v}_{0}$ are expressed in terms of ${T}_{e}$, assuming only polar optical scattering is operative. It is shown that the attenuation rates of the circularly polarized waves traveling in InSb can be reduced and that the slab transmittance ${T}_{s}$ can be enhanced by proper application of static electric field.

Dielectric increment of low molecular weight RNA in dioxane after application of static electric fields

A soluble RNA with a molecular weight between 15 000 and 23 000 was extracted from calf thymus and chromatographically purified. The RNA was slightly soluble in doxane (approx. 2.5 μg/ml) and RNA-dioxane solutions were used to fill a cell (452.02 pF capacitance) to which static electric fields of variable strength were applied. The dielectric permittivity of the solutions was measured at a fixed time interval after the application of the electric field. The RNA solutions showed a dielectric increment proportional to the strength of the applied field and to the RNA concentration. The existence of a hysteresis effect was proven and the effect of the electric field on the RNA molecule might be related to a dielectric saturation phenomenon parallel to long-term changes of the molecule.