Extra Electric Field Research Articles

Study of Nonlinear Current-Voltage Characteristic of Semiconductor Ceramic by the Method of Tilted Energy Band

A analytic method for the calculation of the electrical characteristics of semiconducting ceramics is suggested. This paper put forward the concept of effective carrier concentration. Electrical characteristics under extra electric field have been calculated by the method of tilted energy band. The non-linear current-voltage characteristics with different grain sizes has been obtained. The results pointed out that the current-voltage characteristics divide into three regions: Linear region before breakdown field, nonlinear region near breakdown field and upturn region after breakdown field; The grain boundary barrier leads to the strong non-linear characteristics, which has nothing to do with the grain size. With the grain size decreasing, the breakdown field increases. The results are compared with experimental data.

Ferroelectric modulation on resonant tunneling through perovskite double-barriers

The negative differential resistance (NDR) due to resonance tunneling is achieved at room temperature in perovskite double-barrier heterostructures composed of a 10 unit-cell-thick SrTiO3 quantum well sandwiched in two 10 unit-cell-thick LaAlO3 barriers. The NDR occurs at 1.2 V and does not change with voltage cycling. When the paraelectric SrTiO3 quantum well is replaced by a ferroelectric BaTiO3, the onset of the NDR can be modulated by polarization switching in the ultrathin BaTiO3. A polarization pointing to the collector lowers the NDR voltage but a polarization pointing to the emitter increases it. The shift of the NDR voltage is ascribed to reversal of the extra electric field in the quantum well due to the polarization switching.

Investigating the role of efficiency enhancing interlayers for bulk heterojunction solar cells by scanning probe microscopy

Detailed optimization of the device architecture of bulk heterojunction organic solar cells is of crucial importance when eventually targeting commercial applications. It has been shown before that the efficiency of such devices can be increased significantly upon incorporation of an imidazolium-substituted polythiophene interlayer. The cause of this increase in efficiency was, however, still unclear and is investigated here by a combination of PeakForce Quantitative Nanomechanical Mapping, PeakForce TUNA and Kelvin Probe Force Microscopy. A link between the local morphological and electrical properties is established. We show that the conjugated polyelectrolyte interlayer acts as a hole blocking layer. Additionally, illuminated Kelvin Probe Force Microscopy indicates that the interlayer creates an extra built-in electric field promoting charge transfer from the bulk heterojunction active layer into the interlayer.

Theoretical Calculation of Reorganization Energy for Electron Self-Exchange Reaction by Constrained Density Functional Theory and Constrained Equilibrium Thermodynamics

Within the framework of constrained density functional theory (CDFT), the diabatic or charge localized states of electron transfer (ET) have been constructed. Based on the diabatic states, inner reorganization energy λin has been directly calculated. For solvent reorganization energy λs, a novel and reasonable nonequilibrium solvation model is established by introducing a constrained equilibrium manipulation, and a new expression of λs has been formulated. It is found that λs is actually the cost of maintaining the residual polarization, which equilibrates with the extra electric field. On the basis of diabatic states constructed by CDFT, a numerical algorithm using the new formulations with the dielectric polarizable continuum model (D-PCM) has been implemented. As typical test cases, self-exchange ET reactions between tetracyanoethylene (TCNE) and tetrathiafulvalene (TTF) and their corresponding ionic radicals in acetonitrile are investigated. The calculated reorganization energies λ are 7293 cm(-1) for TCNE/TCNE(-) and 5939 cm(-1) for TTF/TTF(+) reactions, agreeing well with available experimental results of 7250 cm(-1) and 5810 cm(-1), respectively.

The Design of Optical Switch for One-Dimension Photonic Crystal Constructed with TiO<sub>2</sub> and Liquid Crystal

A photonic crystal optical switch based on the electric field control character of the liquid crystal (LC) is proposed and investigated numerically. With the transfer matrix method, it is demonstrated that the band gap appears shifted by varying the angle θ which was between the electric field and the vertical incident light and ranged from 0° to 90°, and the transmission of the 1550nm communication wavelength as the angle θ changes is discussed. It is found that the proposed optical switch is achieved by con controlling on-off of the extra electric field.

Coulomb-potential effects in nonsequential double ionization under elliptical polarization

Using a semiclassical model, we evaluate the correlated electron momentum distribution from nonsequential double ionization (NSDI) of neon in an elliptically polarized laser field. The momentum distribution pattern exhibits a nontrivial change with the increase of the laser ellipticity, which can be understood as a combined effect of the extra laser electric field and the ionic Coulomb potential on the tunnel-ionized electron trajectory. Especially for large ellipticities ($\ensuremath{\epsilon}>0.2$), multiple return collision trajectory contributes dominantly to the NSDI yield and determines the correlated electron momentum distribution, revealing an indispensable role of ionic Coulomb potential in NSDI dynamics under elliptical polarization. Moreover, the nontrivial evolution of the correlated electron momentum distribution with the ellipticity revealed in our model should be testable by a realistic experiment.

Study on the Attenuation Behavior of Acoustic Wave in ER Fluid

The attenuation behavior of acoustic wave in ER fluid which was made by mixing starch in silicon oil was studied through experiments. The results demonstrate that the particle concentration of fluid and the intensity of extra electric field have certain influences on the attenuation behavior of acoustic wave passing through ER fluid. When othe conditions are fixed, the amplitude of acoustic wave passing through ER fluid increases along with the increasing of particle concentration or field intensity; meanwhile, the acoustic wave presents attenuation with the increasing of distance measured, and its trend slows down when the concentration or field intensity increases. The analysis indicates that the solidification effect of ER fluid caused by extra electric field may be the reason for these phenomena.

Spectral shifts of the n → π* and π → π* transitions of uracil based on a modified form of solvent reorganization energy

According to our recent studies on the nonequilibrium solvation, the solvent reorganization energy is found to be the cost of maintaining the residual polarization P', which equilibrates with the extra electric field E(ex). On the basis of this solvent reorganization energy and the well-established equilibrium solvation energy, a novel and reasonable expression for the spectral shift of the electronic absorption spectra is proposed in this work. Furthermore, the two lowest transitions of uracil in aqueous solution are investigated as test cases with the TDDFT/6-311++G** method. The obtained spectral shift is 0.48 eV for n → π* transition and -0.14 eV for π → π* transition, agreeing well with available experimental results. The contributions to the shift are discussed and the electrostatic plus polarization components are found to be crucial for the electronic absorption spectra of uracil in aqueous solution.

Nonequilibrium solvation energy by means of constrained equilibrium thermodynamics and its application to self-exchange electron transfer reactions

This work presents a self-consistent thermodynamic approach to nonequilibrium solvation energy. By imposing an extra electric field onto the nonequilibrium solvation system, a constrained equilibrium state is prepared. New expressions of nonequilibrium solvation energy and solvent reorganization energy have been formulated. The numerical algorithm combining the new formulation with the dielectric polarizable continuum model has been implemented. As an application, self-exchange electron transfer (ET) reactions between tetramethylhydrazine, tetraethylhydrazine, and tetrapropylhydrazine and their corresponding radical cations have been investigated. The inner and solvent reorganization energies are calculated by the "four-point" method and the new method for nonequilibrium solvation, respectively. Besides, we also calculated the electronic coupling matrix. The rate constants for the three self-exchange ET reactions correlate well with experimental results. We have shown that the inner reorganization energies of these self-exchange ET are not very sensitive to compound size while the compound size has some effect on the solvent reorganization energy in acetonitrile. The new method for nonequilibrium solvation energy based on continuum model provides a reasonable result for the solvent reorganization energy.

Voltage effect in PTCR ceramics: Calculation by the method of tilted energy band

A numerical model for the calculation of the electrical characteristics of donor-doped BaTiO 3 semiconducting ceramics is suggested. This paper established a differential equation about electron level on the base of Poisson equation, and solved the equation with Runge–Kutta method. Under extra electric field, electrical characteristics have been calculated by the method of tilted energy band. We have quantitatively computed the positive temperature coefficient of resistivity (PTCR) behavior of donor-doped BaTiO 3 semiconducting ceramics and its voltage effect, and further obtained non-linear current–voltage characteristics with different grain sizes at different temperature. The results pointed out that the resistance jumping is reduced with increasing electric field applied; current and voltage relation follows Ohm's law below Curie temperature, and exhibits strong non-linear above Curie temperature; the non-linear coefficient shows a maximum value at temperature the resistivity reaches maximum and with grain size closed to depletion region width. The results are compared with experimental data.

A Sphere-Interface Model for the Solvent Reorganization Energy in an Electron Transfer Reaction at the Solvent/Conductor Interface

在连续介质理论基础上，根据热力学基本原理，用一个外加电场Eex将非平衡态2[E2^non,D2^non]变成约束平衡态[E2^＊，D2^＊]，推导出了正确普适的溶剂重组能公式．基于球-界面近似，推导出了正确的溶剂-导体界面电子转移溶剂重组能公式．和Marcus的公式相比，本文的结果多了（es-eop）／（eop（es-1））因子．对极性溶剂，预测的溶剂重组能约为Marcus模型所得结果的一半．以C343（Coumarin343）-TiO2体系为算例，计算了溶剂重组能并与实验值进行了比较．

Thermodynamics for nonequilibrium solvation and numerical evaluation of solvent reorganization energy

This work presents a thermodynamic method for treating nonequilibrium solvation. By imposing an extra electric field onto the nonequilibrium solvation system, a virtual constrained equilibrium state is prepared. In this way, the free energy difference between the real nonequilibrium state and the constrained equilibrium one is simply the potential energy of the nonequilibrium polarization in the extra electronic field, according to thermodynamics. Further, new expressions of nonequilibrium solvation energy and solvent reorganization energy have been formulated. Analysis shows that the present formulations will give a value of reorganization energy about one half of the traditional Marcus theory in polar solvents, thus the explanation on why the traditional theory tends to overestimate this quantity has been found out. For the purpose of numerical determination of solvent reorganization energy, we have modified Gamess program on the basis of dielectric polarizable continuum model. Applying the procedure to the well-investigated intramolecular electron transfer in biphenyl-androstane-naphthyl and biphenyl-androstane-phenanthryl systems, the numerical results of solvent reorganization energy have been found to be in good agreement with the experimental fittings.

Instability of Taylor–Couette Flow of Electrorheological Fluid

A linearized instability analysis of Taylor–Couette flow between tworotating concentric cylinders of an electrorheological (ER) fluid iscarried out. The ER fluid exhibits a yield stress in addition to theplastic viscosity when an extra electric-field is applied. It can befound that the yield stress plays a dual role in the flow instability.The possibility of the yield surface falling between the cylinders isanalysed. Although small waves appeared on the yielded surface isconsidered, the yielded surface, which has been treated as a freesurface, has little effect on the flow instability. The effects ofaxisymmetric perturbation on the flow instability are presented due tothe axisymmetric of the basic flow. The parameter β in theyield stress formula of the ER fluid is shown to have distinct effectson the flow instability characteristics.

Anomalies of Doped-LiNbO3 Crystal in Photorefractive Phase Conjugation with Relation to Structural Phase Transformation

We investigate the photorefractive phase conjugation in a Ce:Fe:LiNbO3 crystal as a function of temperature (293-393 K) and find the phase conjugate reflectivity increases sharply in the vicinity of 55, 70 and 110° C. The anomalous phenomenon is possibly concerned with the structural phase transformation of a crystal, which induces an extra internal electric field to influence the phase conjugation. The value of the field is estimated at the order of 105 V/m, in agreement with the published data.

Anomalous temperature character of phase conjugation in doped-LiNbO3 crystal

We report here an anomaly that the photorefractive phase conjugate reflectivity increases sharply near 55, 70, and 110 °C in three different doped-LiNbO3 crystals. The anomalous phenomenon is possibly concerned with the structural phase transformation of the crystal, which induces an extra internal electric field and enhances the reflectivity.

Possibility of studying the internal field in a current-carrying conductor using nuclear quadrupole resonance

A non-invasive method is proposed to probe the Landauer's residual resistivity dipoles in a current-carrying mesoscopic metal. The local voltage fluctuations induce extra local electric field gradients which can then be measured using nuclear quadrupole resonance. We have estimated that such kinds of experiments are indeed feasible.

Layer interactions between dissimilar adsorbates. NH3 layers on chemisorbed CO on Ni(111): A reflection infrared study

Fourier transform infrared reflection absorption spectroscopy (FT-IRAS) has been used to study the adsorption structure of NH3 on top of a saturated CO layer on Ni(111). The IRAS results show that NH3 is adsorbed on top of the saturated CO layer on Ni(111) with its C3v axis tilted away from the surface normal due to the interaction with underlayer CO molecules. Two types of overlayer NH3 species are observed, with one NH3 species exhibiting strong N-H–OC bonding. At the same time, the population of underlayer CO species (bridged and terminal) on different adsorption sites is strongly modified by the adsorption of NH3 molecules in the top layer, with terminal CO decreasing in coverage and bridged CO increasing in coverage. This is due to the influence of an extra (positive-outward) electric field imposed on the CO layer by the polarized NH3 overlayer.

Influence of doping dependent bandgap grading on electrical performance and design criteria of npn Al zGa 1−zAs/GaAs abrupt heterojunction bipolar transistors

Current-voltage characteristics of npn Al z Ga 1− z As/GaAs abrupt heterojunction bipolar transistors (HBTs) with nonuniform doping in the emitter and the base has been studied in some details. For the calculation of these characteristics the effects of both conduction band potential spike ΔE b and valence band discontinuity ΔE v have been taken into account. The extra electric field generated due to nonuniform base doping accelerates the flow of electrons, and minimizes the effect of ΔE v on the electron current density J c.

Cracked-Stripe Resistance and Current Crowding Effect

The contribution of a stripe cracking to its resistance is obtained in a closed form by means of Christoffel-Schwarz transformation. It is shown that the cracked region resistance is a sum of two terms in series: one is the typical resistance term which is linearly proportional to the width and inversely proportional to the cross section of the stripe, the other depends sensitively upon the perpendicular depth of the crack, known as the current crowding resistance. Some numerical results for the crack region resistance are presented. The extra local electric field, its corresponding mass flux and their potential implications to electromigration arc also discussed.