Amplitude Of Ac Electric Field Research Articles

Asymmetric temporal variation of oscillating AC electroosmosis with a steady pressure-driven flow

In most electrokinetic flows in micro-/nanofluidics, electroosmotic flow (EOF) is always a fundamental phenomenon. When an external AC electric field is applied, there will be a transient EOF velocity, which is crucial for understanding the mechanism of the unsteady AC EOF. However, the transient flow velocity cannot be experimentally measured with sufficiently and simultaneously temporal and spatial resolution. Here we report that under a strong AC electric field, an asymmetric temporal variation of oscillating EOF (OEOF) can be generated near the electric double layer (EDL) on the bottom wall of a microchannel. The flow is measured by laser-induced fluorescence photobleaching anemometer (LIFPA). Both the flow velocity of the OEOF and the linearly related internal electric field in the microchannel are theoretically governed by an inviscid Burgers’ equations with an external forcing term and controlled by two coefficients which represent the magnitudes of linear ( $${Z}_{l}$$ ) and nonlinear ( $${Z}_{nl}$$ ) terms. These two coefficients are separately determined by five dimensionless parameters, including Stokes number ( $${St}$$ ), aspect ratio ( $$\gamma$$ ), Schmidt number ( $${Sc}$$ ), Peclet number of mean flow velocity ( $${P}_{e, U}$$ ) and Peclet number of electrophoresis ( $${P}_{e, {EP}}$$ ). In this work, the influence of $${P}_{e, U}$$ and $${P}_{e, {EP}}$$ which are tightly related to the local mean flow velocity and the amplitude of AC electric field is investigated. When the electric field is low, $${P}_{e, U}\gg {P}_{e,{EP}}$$ and accordingly $${Z}_{l}\gg {Z}_{nl}$$ , a temporal symmetry of the time series of velocity is observed. However, when the electric field is high, $${P}_{e, U}\ll {P}_{e, {EP}}$$ and $${Z}_{l}\ll {Z}_{nl}$$ , then the periodicity and temporal symmetry of OEOF can be significantly broken and a temporal asymmetry of the time series of velocity is resulted in, especially under the square wave external electric field. We also find increased mean flow velocity and saturation of velocity fluctuations with the increasing electric field. This work provides a new methodology to study unsteady electrokinetic flows.

Composite fermions in a wide quantum well in the vicinity of the filling factor 1/2

Using acoustic method we study dependences of transverse AC conductance, σ(ω), on magnetic field, temperature and the amplitude of AC electric field in a wide (75 nm) quantum well (QW) structure focusing on the vicinity of the filling factor ν = 1/2. Measurements are performed in the frequency domain 30–307 MHz and in the temperature domain 20–500 mK. Usually, in wide QW structures closely to ν = 1/2 the fractional quantum Hall effect (FQHE) regime is realized at some parameters of the sample. However, in our structure, at ν = 1/2 it is a compressible state corresponding to gas of composite fermions which is observed. This is confirmed by apparent frequency independence and weakly decreasing temperature dependence of Re σ(ω). Comparing the dependences of this quantity on temperature and power of the acoustic wave we conclude that the observed nonlinear behavior of the conductance is compatible with heating of the composite fermions by the acoustic wave. For comparison, we also study the vicinity of ν = 3/2 where the FQHE regime is clearly observed.

Magnetic Minibands and Electron–Electron Bound States in Ac-Driven Graphene with Space-Modulated Gap

The emergence of the magnetic minibads in the quasienergy spectrum of graphene superlattice subjected to the quantizing magnetic field and electromagnetic radiation was investigated. The graphene superlattice was assumed to be formed by space-periodical modulation of the gap in the vicinity of the Dirac point of the graphene band structure. The explicit form of the Floquet spectrum of electron was derived in the case of weak spatial modulation. Minibads widths were shown to change with ac electric field amplitude. The possibility of electron-electron bound states was shown. The binding energies of these states were shown to be the function of the amplitude of ac electric field.

Magnetoelectric properties of 500-nmCr2O3films

The linear magnetoelectric effect was measured in 500 nm Cr2O3 films grown by rf sputtering on Al2O3 substrates between top and bottom thin film Pt electrodes. Magnetoelectric susceptibility was measured directly by applying an AC electric field and measuring the induced AC magnetic moment using superconducting quantum interference device magnetometry. A linear dependence of the induced AC magnetic moment on the AC electric field amplitude was found. The temperature dependence of the magnetoelectric susceptibility agreed qualitatively and quantitatively with prior measurements of bulk single crystals, but the characteristic temperatures of the film were lower than those of single crystals. It was also possible to reverse the sign of the magnetoelectric susceptibility by reversing the sign of the magnetic field applied during cooling through the N\'eel temperature. A competition between total magnetoelectric and Zeeman energies is proposed to explain the difference between film and bulk Cr2O3 regarding the cooling field dependence of the magnetoelectric effect.

Effect of interaction between AC electric field and phonon oscillation of metal cluster on tip-growth of carbon nanotube

The paper reports effect of interaction between AC electric field and metal cluster sitting at tip end of the carbon nanotube (CNT) on CNT tip-growth in CVD theoretically. For this purpose, a theoretical model based on phonon oscillations of the metal catalyst and influence of AC electric field on these oscillations is presented. Results show that there is an optimum AC electric field which optimizes growth of ultra-long CNTs. Then it is demonstrated that, in comparison with CNTs in the absence of field, CNTs under optimum electric field grow more. In addition, relation between optimum temperature and amplitude of AC electric field is investigated and it is shown that increasing electric field leads to higher optimum temperature. Finally, Investigation of effect of catalyst type on optimum electric field demonstrates the optimum field for various catalysts is different due to their different characteristics including van der Waals interaction with carbon, atomic mass and number of free charge carriers per each atom. All results are discussed and interpreted.

Magnetic quantum ratchet effect in Si-MOSFETs

We report on the observation of magnetic quantum ratchet effect in metal-oxide-semiconductor field-effect-transistors on silicon surface (Si-MOSFETs). We show that the excitation of an unbiased transistor by ac electric field of terahertz radiation at normal incidence leads to a direct electric current between the source and drain contacts if the transistor is subjected to an in-plane magnetic field. The current rises linearly with the magnetic field strength and quadratically with the ac electric field amplitude. It depends on the polarization state of the ac field and can be induced by both linearly and circularly polarized radiation. We present the quasi-classical and quantum theories of the observed effect and show that the current originates from the Lorentz force acting upon carriers in asymmetric inversion channels of the transistors.

Mesoscopic relaxation time of dynamic image correlation spectroscopy

Dynamical images contain useful information of how the objects behave in time and space. When the system is in biological fluids, the motion of the object is much over-damped; the relaxation time is the characteristics in a diffusive time scale. We have found dynamical states of melting and forming of small nematic domains (10—30 μm) that are exhibited in the suspensions of fd-viruses under applied AC electric field amplitude at low frequency. Dynamic image correlation function is used for extracting the mes- oscopic relaxation times of the dynamical states, which can be employed as an application to other dynamic imaging process of biologically relevant soft condensed matter and biomedical systems.

Bloch electron spontaneous emission from a single energy band in a classical ac field

A theory for the spontaneous emission of radiation for a Bloch electron in a single superlattice (SL) energy band under the influence of an external, spatially homogeneous, classical ac electric field is presented. The classical external ac electric field is described in the vector-potential gauge. The quantum radiation field is described by the free-space quantized electromagnetic field in the Coulomb gauge. Utilizing the instantaneous eigenstates of the Bloch Hamiltonian as the basis states, the Bloch electron dynamics is described to all orders in the classical ac electric field. It is shown that the spontaneous emission occurs with frequencies equal to integral multiples of the classical ac electric field frequency; this is due to the imposition of temporal periodic motion of the Bloch electrons in the SL miniband from the external periodic ac field. From appropriately derived selection rules for photon frequency and wave-vector transitions, the total spontaneous-emission probability (TSEP) is derived to first-order perturbation theory in the quantized radiation field. A general expression is obtained for the TSEP in terms of arbitrary SL miniband parameters; further, the TSEP is analyzed in detail based on the band model for the nearest-neighbor tight-binding approximation, and results show multiharmonic behavior and ac electric field tuning properties. In the nearest-neighbor tight-binding approximation, specific results for single Bloch electron manifest distinct plateaulike step structure in the analysis of normalized TSEP as a function of the ratio ${\ensuremath{\omega}}_{0}/\ensuremath{\omega}$, where ${\ensuremath{\omega}}_{0}$ is the characteristic frequency, proportional to the ac electric field amplitude, and $\ensuremath{\omega}$ is the ac electric field frequency; the plateau centers of gravity are found to be defined by the Stark delocalization condition established in ac-field transport. Further, the influence of a microcavity waveguide is established and shows enhancement as well as harmonic tuning of the TSEP due to coupling to the microcavity modal environment. Finally, the one-electron TSEP is extended, within the independent electron approximation, so as to include fractional band filling along with a constant-temperature-dependent and electron-density-dependent analysis; from this analysis, TSEP numerical estimates are projected at terahertz external field frequencies for a half-filled GaAs/AlGaAs SL miniband at zero temperature.

Bending Behavior of Functionally Graded Piezoelectric Laminated Actuators under Electric Fields

We present numerical and experimental results on the nonlinear bending behavior due to domain wall motion in functionally graded piezoelectric actuator under alternating current (ac) electric fields. A nonlinear finite element method is employed to analyze the dynamic response of functionally graded piezoelectric actuator. A phenomenological model of domain wall motion is used in computation, and the effects of ac electric field amplitude and frequency, number of layers, and property gradation on the deflection of the cantilever actuators are examined. Experimental results, which verify the model, are presented using a functionally graded bimorph. The numerical results agree very well with the experimental values.

Dynamic Dielectric Nonlinearity in Epitaxial Thin-Film Relaxors and Ferroelectrics

The dynamic dielectric response of epitaxial thin-film PbMg1/3Nb2/3O3, PbSc0.5Nb0.5O3, and Ba0.4Sr0.6TiO3 was experimentally studied as a function of temperature, frequency, and amplitude of ac electric field (to 10 MV/m). In thin-film relaxors at all amplitudes, a glasslike behavior was evidenced by Vogel-Fulcher relationship, scaling of the dielectric peak, and broadening of the relaxation time spectra on cooling. Both this and the nonlinear dielectric response were consistent with reorientation of randomly interacting dipoles at presence of random fields. In thin-film ferroelectrics, a relaxorlike nonlinear dielectric behavior was found. As a reason for this, possible coexistence of polar and nonpolar regions was discussed.

Threshold behavior of the dielectric nonlinearity in ferroelectric crystals of triglycine sulfate

The threshold behavior of the effective permittivity and harmonic amplitudes of the polarization switching-current spectrum is studied for triglycine-sulfate crystals with various defects as a function of the ac electric field amplitude. The interaction energies are calculated for domain walls with defects. The relaxation behavior of the effective permittivity at a constant amplitude of the switching field is studied.

Nonlinear Dynamic Bending and Domain Wall Motion in Functionally Graded Piezoelectric Actuators under AC Electric Fields: Simulation and Experiment

This paper describes the results of our numerical and experimental studies of the nonlinear bending behavior due to domain wall motion in functionally graded piezoelectric actuator under alternating current electric fields. A nonlinear three-dimensional finite element method is employed to simulate the dynamic response of cantilever functionally graded piezoelectric actuator. A phenomenological model of domain wall motion is used in computation, and the effects of ac electric field amplitude and frequency, number of layers, and property gradation on the deflection and internal stresses of the functionally graded bimorphs are examined. It is shown that the predicted deflection results, obtained from the numerical model, agree well with the corresponding experimental results.

Effect of ac field on the dielectric behavior in epitaxial films of relaxor ferroelectricPbMg1∕3Nb2∕3O3

The dynamic dielectric response of epitaxial $\mathrm{Pb}{\mathrm{Mg}}_{1∕3}{\mathrm{Nb}}_{2∕3}{\mathrm{O}}_{3}$ thin films was experimentally studied as a function of amplitude of ac electric field including very large amplitudes (to $10\phantom{\rule{0.3em}{0ex}}\mathrm{MV}∕\mathrm{m}$). For all amplitudes, a typical glasslike relaxor behavior was evidenced by the Vogel-Fulcher relationship, empirical scaling of the dielectric peak, and a broadening of the relaxation time spectra on cooling. With increasing amplitude of the ac field, both the temperature of the dielectric maxima and the freezing temperature decreased, the relaxation time spectrum became narrower, and the nonlinear permittivity was nonmonotonic. The comparison of the observed dielectric behavior with that under an applied small dc electric field and with the results of modeling revealed an orientational contribution to polarization.

Phase diagram of thin-film relaxor PbMg1∕3Nb2∕3O3

Epitaxial heterostructures of pure perovskite relaxor ferroelectric PbMg1∕3Nb2∕3O3 thin films were grown by pulsed laser ablation varying the temperature of deposition. Dielectric response of the films was studied as a function of frequency, temperature, amplitude of ac electric field, and magnitude of dc electric field. The temperatures of dielectric maxima and the freezing temperatures determined in different regimes were analyzed with respect to the microstructure of the films. Different nonmonotonic tendencies in the behavior of the characteristic temperatures were found. The shift of the electric-field–temperature phase diagram of PbMg1∕3Nb2∕3O3 involving the sequence of transformations between paraelectriclike, glasslike, and ferroelectriclike states was suggested to be responsible for this. The shift of the phase diagram was found to be a monotonic function of the in-plane strain and it was ascribed to the internal electric field.

Coexistence of ferroelectric and relaxor properties in epitaxial films of Ba1−xSrxTiO3

Dielectric response of epitaxial thin films of perovskite ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{TiO}}_{3},x=0$, 0.2, 0.6, was experimentally studied as a function of temperature, frequency, and amplitude of ac electric field. Decrease of temperatures of dielectric maxima ${T}_{m}$ with respect to those in bulk, Curie-Weiss behavior above ${T}_{m}$, and ferroelectriclike behavior around ${T}_{m}$ were found to coexist with relaxorlike behavior below ${T}_{m}$. The results are discussed in terms of the frustrated transition between two ferroelectric phases in the films.

Properties of ferroelectric PbTiO3 thin films

PbTiO 3 thin films were prepared from alkoxide solution precursors and crystallized onto Pt/TiO2/SiO2/Si substrates. Microscopy observations revealed that the complexity of the domain walls structure decreased with the grain size. Dielectric, electrostrictive, and piezoelectric properties of the films were characterized in details. A shift of the temperature of the dielectric permittivity maximum due to stresses in the plane of films has been observed. Electrostrictive M and Q coefficients were estimated by measuring strain as a function of the ac electric field amplitude. The d33 vs Edc loops are rectangular with a maximum weak field piezoelectric d33 coefficient equal to 65 pm/V. The dielectric permittivity and piezoelectric nonlinearities can be explained by taking into account domain-walls contributions. Dielectric and piezoelectric aging was investigated. It was found that both coefficients follow logarithmic time dependence, with comparable rates. The aging behavior in the PT films is thus qualitatively closer to that in ceramics than in thin films of lead zirconate titanate.

Hysteresis phenomena in the course of polarization evolution in a sinusoidal electric field in lead magnesium niobate crystals

The processes of polarization evolution in single crystals of the PbMg1/3Nb2/3O3 model ferroelectric relaxor in a sinusoidal electric field are investigated at temperatures near and above the temperature Td0 of destruction of the induced ferroelectric state upon heating in zero electric field. The polarization switching current loops are measured in the ac electric field applied along the 〈111〉 and 〈110〉 pseudocubic directions. The electroluminescence intensity loops are obtained under the combined action of ac and dc electric fields applied along the 〈100〉 direction. In a certain temperature range above Td0 and the freezing temperature Tf in lead magnesium niobate, there are electric current anomalies, that correspond to the dynamic formation and subsequent destruction of the ferroelectric macroregions throughout each half-cycle of the ac electric field. The measurements of electroluminescence hysteresis loops demonstrate that the observed depolarization delay (related to the ac electric field amplitude) increases with an increase in the dc electric field and decreases as the ac field amplitude increases. The nature of the observed phenomena is discussed.

Degradation of asymmetrical Pt/SRO/PLZT/Pt capacitors: Role of Pt and oxide electrodes

Role of Pt and SRO electrodes in polarization fatigue of PLZT film ferroelectric capacitors is studied. We show that asymmetrical Pt/SRO/PLZT/Pt structure exhibits unusual dependence of the endurance of switching polarization on the driving ac electric field amplitude. Specifically, for high ac electric field amplitude it shows a good switching endurance similar to SRO/PLZT/SRO capacitors, whereas for amplitude lower than 80 kV/cm a pronounced polarization fatigue similar to that of conventional Pt/PLZT/Pt capacitors is observed. Based on the analysis of these results we conclude that the polarization switching endurance under high-amplitude fatiguing cycling is governed only by the top SRO-interface which is not subjected to degradation, whereas the degradation properties of the bottom Pt-interface do not play any role.

Top-interface-controlled switching and fatigue endurance of (Pb,La)(Zr,Ti)O3 ferroelectric capacitors

Mechanisms of polarization switching and fatigue in (Pb,La)(Zr,Ti)O3 (PLZT) films are studied by comparative analysis of degradation and leakage conduction of PLZT capacitors with Pt, SrRuO3 (SRO), and layered Pt/SRO (80/5 nm) electrodes. It is found that the asymmetrical Pt/SRO/PLZT/Pt structure exhibits a good fatigue performance in combination with low leakage like that on identically processed Pt/PLZT/Pt capacitor. This asymmetrical structure exhibits very unusual dependence of the endurance of switching polarization on the driving alternating-current (ac) electric field amplitude. Specifically, for high ac electric field amplitude it shows good switching endurance similar to SRO/PLZT/SRO capacitors, whereas for amplitude lower than 80 kV/cm a pronounced polarization fatigue similar to that of the conventional Pt/PLZT/Pt capacitors is observed. Based on the analysis of our results on fatigue and leakage conduction we conclude that: (i) In asymmetrical Pt/SRO/PLZT/Pt system the physical mechanisms of polarization switching vary depending on the driving voltage amplitude. The polarization switching endurance under high-amplitude cycling is governed only by the top SRO interface, whereas the degradation properties of the bottom Pt interface do not play any role. On the contrary, for driving voltage amplitudes lower than 80 kV/cm the bottom Pt-interface degradation is a limiting factor for the fatigue performance. (ii) The fatigue in PZT films is controlled by a mechanism related to the inhibition of near-by-electrode nucleation of opposite domains, as suggested earlier.

Nonlinear self-channeling of a laser beam at the surface of a photorefractive fiber

We experimentally observed the self-channeling of the light beam in photorefractive Bi12TiO20 fiberlike sample owing to the strong fanning effect. It results in significant speed up of the photorefractive response time in waveguides and in anomalous dependence of the response time on the applied ac electric field amplitude: the higher electric field, the faster response.