Stepwise Electric Field Research Articles

Neat Temporal Performance of InGaAs/InAlAs Single Photon Avalanche Diode With Stepwise Electric Field in Multiplication Layers

We have incorporated a novel design of stepwise electric field in the multiplication layers to the InGaAs/InAlAs single photon avalanche diodes (SPADs). The stepwise electric field profile aims to circumvent the dilemma between dark count rate, afterpulsing and temporal performance. SPADs with large ( $240~\mu \text{m}$ ) and small ( $25~\mu \text{m}$ ) active area are fabricated and characterized. The intrinsic temporal response for large and small SPADs has a full-width at half maximum of 72 and 67 ps respectively. Importantly, the diffusion tail exhibits only about 200 ps full-width at one-thousandth maximum, showing fast and neat temporal characteristics. Such devices also present reasonable dark count rate of $5\times 10^{6}$ Hz and $3\times 10^{7}$ Hz and moderate single photon detection efficiency of 32 % and 27 % at about 200 K respectively for large and small devices, manifesting that the avalanche build-up time can be improved without losing the detection performance using our specific design and optimized electric field distribution. Such improvement in temporal performance of SPADs should facilitate their capability in the applications of time-correlated single photon counting and light detection and ranging.

Infrared spectroscopic study on electric-field-induced dynamics of polymer chains in a ferroelectric melt-quenched cold-drawn film of nylon-12

We studied the intensity changes of the infrared bands of a ferroelectric melt-quenched, cold-drawn film of nylon-12 as a function of an external cyclic stepwise electric field with the polarization perpendicular to the draw direction. The infrared bands assigned to the NH stretching and amide I modes exhibited butterfly-shaped hysteresis loops characteristic of ferroelectric materials, whereas the intensity changes of the infrared bands assigned to the CH2 antisymmetric and symmetric stretching modes were small and showed no butterfly-shaped hysteresis loops. These results indicate that only the amide groups were inverted under the external electric field. We proposed a molecular mechanism explaining the ferroelectric properties of nylon-12: the amide groups in the antiparallel β-sheet structure are inverted by the external electric field to form new hydrogen bonds, generating two stable states in a nearly double-minimum potential.

Stepwise electric field induced charging current and its correlation with space charge formation in LDPE/ZnO nanocomposite

This study intends to establish the correlation between charging current under stepwise increased electric field and space charge formation in low density polyethylene (LDPE) and LDPE/ZnO nanocomposites. By applying stepwise increased electric field, the charging current and space charge distribution were measured as a function of time under 10, 30 and 50 kV/mm, respectively. The results show that homopolar space charge formation induces increasing charging current with time, while heteropolar space charge formation induces decaying charging current and excellent space charge suppression is accompanied by constant charging current with time. The abundant deep trapping states introduced by nanofillers dominate both the lower steady charging current and space charge suppression in the nanocomposite. The results indicate that charging current behavior induced by stepwise increased electric field is extremely informative and is feasible to be a direct method for rough estimation of space charge formation and suppression in polymer dielectrics. Addition of ZnO nanofillers suppresses space charge accumulation in LDPE, indicating LDPE/ZnO nanocomposite is a potential insulation material for high voltage direction current cables.

Evaluation of FEM electric field analysis using the electric properties of giant unilamellar vesicles (GUV) and Jurkat cells measured by electrorotation spectroscopy: Introduction of cryo‐ and lyoprotectants by electrofusion of GUVs and living cells

AbstractElectrofusion of giant unilamellar vesicles (GUVs) and living cells is a gentle method for delivering membrane impermeable cryo‐/lyo‐protective molecules into living cells for cryo‐/lyopreservation. In this method, an optimal length and strength of an electric pulse are required to initiate GUV‐cell fusion. Calculating the electric field by the finite element method (FEM) might be a powerful analytical method for prediction of the optimal pulse length and strength of a deformed and adhered GUV‐cell. The objective of this study is to clarify whether an FEM model of a pulsed GUV or cell could be applicable for prediction of its electric field, especially the change of membrane potential. First, electric properties of GUVs and Jurkat cells were derived from electrorotation spectra with a dipole approximation model. Secondly, the electric field and the membrane potential of a single GUV or cell after applying a stepwise electric field were calculated by an FEM model using the measured electric properties. At the first stage after applying a step electric field, the calculated membrane potential by the FEM model shows good agreement with the membrane potential derived from the dipole approximation model. After complete relaxation of the electric field, the calculated membrane potential of the FEM model is lower than that of the dipole approximation model. This might be because both models do not take into account the effects of electric double layers on both sides of the membrane. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20242

Piezoelectric resonance of lead zirconate titanate ceramics excited by a stepwise electric field

Transient current of ferroelectric ceramics has been intensively studied using a stepwise electric field. Abnormal oscillations were observed in the transient current when a stepwise electric field was applied onto modified lead zirconate titanate (PZT) ceramic samples in a very short time (less than 100ns) in the present study. Compared to the frequency spectrum of those samples, it is found that those frequencies of oscillations correspond to that of piezoelectric resonance. Four samples of PZT ceramics were cut into different dimensions according to the requirement of five different electromechanical coupling modes. Experimental results demonstrate that those five piezoelectric resonance modes of the ferroelectric samples could be excited by a stepwise electric field, and different resonance modes of a sample could be excited simultaneously. The authors also found that whether piezoelectric resonance could be excited depends on the parameters of test circuit.

Determination of room-temperature creep of soft lead zirconate titanate piezoceramics under static electric fields

This study focuses on the experimental investigation of the time-dependent effects of a commercial soft lead zirconate titanate material at room temperature. Samples in initially unpoled states were subjected to a cyclic stepwise electric field which was kept constant at different levels for 300 s. Due to ferroelectric domain switching, significant nonlinearity and hysteresis were observed in the overall polarization and strain response. In particular, the material exhibited creep behavior as the applied electric field was held constant over extended periods of time. This creep was caused by microscopic domain switching processes induced gradually during the holding time. The creep was of primary or transient type in nature and depended strongly on the magnitude of the load applied. Most pronounced creep was observed when holding the field close to the coercive field. Logarithmic representation of the polarization or strain versus time curves indicated that the creep behavior could be quantified approximately by the Andrade power law. The creep exponents were determined for different field conditions. The results may help the understanding of the creep mechanism, which in turn provides contributions to improve the performance and reliability of ultrahigh-precision positioning piezoactuators.

Strong azimuthal anchoring energy at a nematic-polyimide interface

Some years ago we proposed an automated reflectometric method to measure the director azimuthal angle at the interface between a nematic liquid crystal and another medium. The method ensures a great accuracy and sensitivity and is virtually unaffected by the presence of a director bulk distortion. This latter property makes it possible to measure strong anchoring energies. In the present experiment, we use this method to measure the azimuthal anchoring energy at the interface between the nematic liquid crystal 4-pentyl-4-cyanobiphenyl (5CB) and a rubbed polyimide layer. This kind of interface is characterized by a strong azimuthal anchoring and, thus, it represents a good test for the proposed reflectometric method. An ac planar electric field is applied to a nematic layer and the consequent azimuthal rotation of the director at the interface is measured. The anchoring energy coefficient Wa at room temperature is strong (Wa=0.33 x 10(-3) J/m2) and decreases greatly as the clearing temperature is approached. The time response of the azimuthal surface director angle to a stepwise electric field evidences the characteristic slow dynamics which is currently observed for weak anchoring substrates.

Observation of piezoelectric resonance in time domain transient current of ferroelectric ceramics and crystals

An abnormal resonance behavior was observed from the transient current in the time domain for both ferroelectric ceramics and single crystals excited with a stepwise electric field. The phenomenon can be accounted for as piezoelectric resonance. Corresponding resonant peaks in the frequency spectrum of impedance verified the piezoelectric origin of the abnormal resonance. Using a RLC series equivalent circuit of the piezoelectric resonance model, the resonance behavior of the transient current can be calculated and well fitted with experiments.

Dynamic Responses of Zeolite-based ER Fluid Sheared between Two Concentric Cylinders

A Zeolite-based ER fluid was sheared in a cup-bob unit under stepwise electric field excitation. The shear stress of the ER fluid, electric current and the applied electric potential during the transient phase were recorded simultaneously with a data-acquisition system. The experiment results show that there exists a delay time of approximately 0.3 ms in shear stress following the change in electrical potential. The delay time corresponded to the time needed for the charging and the discharging of the ER fluid cell at the moments of field-on and field-off respectively, and was not influenced by the field strength and the shear rate. This result implies that the shear resistance of ER fluid does not change in the polarization and de-polarization processes. With the increase in shear rate, transient periods of stress build up and decay occurred at the switching on and switching off moments following an exponential pattern. The response time of ER fluid is discussed in the context of the designing of ER devices.

Time scales for structural formation in an electrorheological suspension probed by optical and electrical responses

Responses of the diffuse transmitted light intensity and the current passing through an electrorheological suspension to the stepwise electric field were measured in the quiescent state, and the time scales for the structural formation of the polarized particles were reported. It was found experimentally that both of the responses consist of plural modes, the faster and slower modes even in the quiescent state. The optical response was also expressed as an exponential function with two modes, which take place in succession.

Ferroelectric Switching Characteristics and Crystal Structure of Nylon 11

The time domain measurement of polarization reversal is made for melt-quenched, uniaxially-drawn and annealed Nylon 11 samples by applying a stepwise electric field. The amount of reversed polarization of an as-drawn sample is almost independent of the field strength above 80 MV m−1 and gives a value of ca. 50 mC m−2. The switching time is proportional to a power of the field strength. Annealing above 100°C causes a marked increase in switching time but does not change the amount of reversed polarization. X-Ray study shows that annealing results in a change in crystal structure from a pseudohexagonal phase containing distorted conformation into an all-trans triclinic phase. Such a structural change enlarges the potential barrier against the chain rotation to result in the increase in the switching time.

INACTIVATION of E. COLI FOR FOOD PASTEURIZATION BY HIGH-STRENGTH PULSED ELECTRIC FIELDS

Pulsed electric fields of very high field strength and short duration are effective in the inactivation of E. coli. Nine log reduction in E. coli viability was achieved using a stepwise pulsed electric field treatment where E. coli suspensions were treated repeatedly in batches. It was demonstrated that high-strength pulsed electric field treatment is adequate for pasteurization of liquid foods. A 40,000 volt pulse generator was constructed to supply high voltage electric pulses to a treatment chamber with two parallel plate stainless steel electrodes where fluid food was contained. the gap between electrodes was 0.51 cm and the chamber volume was 14 ml. Pulse electric field strength ranged from 35 to 70 kV/cm. Pulse width was selected at 2 μs. Number of pulses per treatment varied from 1 to 80. E. coli were suspended in a simulated milk ultra-filtrate (SMUF) and treated with pulsed electric fields in a batch mode. the suspension fluid was maintained at constant temperatures of 7, 20, or 33C. Maximum temperature change occurring during each pulse was 0.3C measured by a fiber optics temperature probe. E. coli viability before and after treatment were assayed by counting colony forming units (cfu).

On mixing of 2p53s excited neon atoms in highly non-equilibrium plasma

The experimental study of highly non-equilibrium neon plasma has been carried out when the 2p53s excited state atom density essentially exceeds the electron concentration. The initial electron density Neo was between 109 and 1010 cm-3, the density of the ground-state atoms N was within the limits 1017-1018 cm-3 and the reduced electric field E/N varied between 5 and 25 Td. The plasma was created as a result of an interaction between the stationary background and the pulsed electric fields. The excited atom and electron density growth induced by the stepwise electric field variations were found to be of an explosive character due to the accumulation of atoms in the lowest-lying excited states. The binary chemi-ionization reactions of the excited atoms were shown to play the principal role in the kinetics of the excited atoms and electrons. Due to the generation of fast electrons during the chemi-ionization processes, the electron energy distribution function was found to be a highly non-equilibrium one.

Radiation spectroscopy of non-stationary plasma at high densities of excited noble-gas atoms

Theoretical and experimental study of the ionization-recombination relaxation in the pulsed discharge plasma has been carried out at high density of the excited noble-gas atoms. The background electron density Neb was between 109 and 1010 cm-3, the density of the neutral atoms Na was within the limits 1017-1018 cm-3, and the reduced electric field E/Na varied between 5 and 25 Td. The excited atom and electron density growth induced by the stepwise electric field variations was found to be of an explosive character due to the accumulation of atoms in the lowest electronically excited states. When the excited atom density exceeds the electron concentration essentially, the binary chemi-ionization reactions of the excited atoms were shown to play a principal role in the kinetics of the excited atoms and electrons. The theoretical description was performed in comparison with the experimental study of the kinetics of the excited atoms and electrons. Approximate analytical expressions have been obtained for the de-excitation development. The theoretical model allows calculation of the temporal dependence of the emission spectra and the determination of the effective rate coefficients of the direct excitation by electron impact from the ground state to the np5(n+1)s levels. The effective rate coefficients of the chemi-ionization processes for binary collisions between excited noble gas atoms have also been obtained. Calculation and experiment are in good agreement.