High Electric Field Region Research Articles

Study of the transmembrane potential distribution of cell pairs in a microfluidic device using polymer obstacles to initiate electrofusion

In this paper, we investigate the different parameters that affect the distribution of the transmembrane potential of cells brought into contact before electrofusion in a miniaturized fluidic device. In particular, we discuss the deviation of the effective transmembrane voltage compared to the one predicted by Schwan’s law. The application of electric field pulses to biological cells induces a transmembrane potential which leads to cell permeabilization. Electrofusion occurs when several cells are brought into contact while they are electropermeabilized. Nevertheless, we show that in this case, the mutual presence of cells interferes on Schwan’s equation. Consequently, the transmembrane voltage at the cell contacting point is drastically reduced, which is not favorable for an electrofusion in smooth conditions, as the applied voltage needs to be increased to compensate this phenomenon. We show that the introduction of polymer obstacles reverses this trend, as the high electric field region is focused on the fusion zone. To confirm the theory we developed, quantitative biological experiments are presented in which murine melanoma cells were paired and fused in both conditions (with and without obstacles).

Characterization of ZrTiO4 thin films prepared by sol–gel method

The electrical properties, memory switching behavior, and microstructures of ZrTiO4 thin films prepared by sol–gel method at different annealing temperatures were investigated. All films exhibited ZrTiO4 (111) and (101) orientations perpendicular to the substrate surface, and the grain size increased with increasing annealing temperature. A low leakage current density of 1.47×10−6A/cm2 was obtained for the prepared films. The I–V characteristics of ZrTiO4 capacitors can be explained in terms of ohmic conduction in the low electric field region and Schottky emission in the high electric field region. An on/off ratio of 102 was measured in our glass/ITO/ZrTiO4/Pt structure with an annealing temperature of 600°C. Considering the primary memory switching behavior of ZrTiO4, ReRAM based on ZrTiO4 shows promise for future nonvolatile memory applications.

Growth and characterization of lead-free piezoelectric BaZr0.2Ti0.8O3–Ba0.7Ca0.3TiO3 thin films on Si substrates

Lead-free piezoelectric BaZr0.2Ti0.8O3–Ba0.7Ca0.3TiO3 (BCZT) thin films were grown on La0.7Sr0.3MnO3-buffered Si (001) by off-axis RF magnetron sputtering at temperatures ranging from 550 to 810°C. In this article, we present the detailed investigation on structure, leakage current behaviors and electromechanical properties of BCZT thin films. The crystallographic texture and grain size of the as-grown thin films are strongly dependent on the growth temperature, which consequently affects the leakage behaviors and local electromechanical properties. The crystallographic orientation becomes better and the grain size increases when increased the substrate temperature. The dominant leakage mechanism is found to be space-charge-limited conduction at low electric field, while a Fowler-Nordheim tunneling is confirmed in high electric field region for the films deposited at 710°C and 810°C. The increasing growth temperature also leads to remarkable improvement in the local electromechanical properties of the films. The BCZT film deposited at an optimal temperature of 810°C exhibits a considerably high effective piezoelectric coefficient d33,f of 94±4pm/V, which is comparable to that of a typical lead zirconate titanate thin film.

Safety Distance Determination for 500 kV AC Transmission Line’s Helicopter Inspection

As an efficient and advanced line inspection method, helicopter line patrol is gradually more and more used in transmission lines inspection, promoting the elaborate operation of transmission lines and reducing the management cost. However, as a 'floating-potential conductor' near to a high-voltage transmission line, the helicopter would be at a high electric field region; and bring security risk to equipment and operating personnel. In this paper, the electric field strength near the cabin at locations of different distance from transmission lines is investigated by calculation, and the field in the helicopter cabin is also calculated with finite element method (FEM). The result indicates that the potential difference becomes higher with the decrease of the distance between the helicopter and transmission line. Considering the discharge energy and the guarantee of the persons’ safety, the safety distance is determined as d≥15 m.

Structural and electrical properties of Sm-substituted BiFeO3 thin films prepared by chemical solution deposition

The structural and electrical properties of chemical-solution-deposited Bi1−xSmxFeO3 (x=0, 0.025, 0.05, 0.075, 0.1) thin films on Pt/Ti/SiOx/Si (100) substrates were investigated. Films up to 5at.% Sm exhibited a single perovskite phase with rhombohedral structure, whereas films with 7.5 and 10at.% Sm exhibited a distorted orthorhombic crystal structure. Atomic force microscopy of the films showed homogeneous and smooth surface. Films with 7.5at.% Sm exhibited significant reduction in leakage current in the high electric field region and improved breakdown characteristic. The polarization vs. electric field (P–E) hysteresis loops were recorded in a 100nm thick film with 3V coercive voltages. Moreover, well saturated P–E hysteresis loops with high polarization (80μC/cm2) and low coercive field (300kV/cm) were also recorded in 100nm thick films with low coercive voltage (5V). The Sm-substitution in BiFeO3 improved the fatigue endurance with no significant degradation in polarization even after 108 fatigue cycles. These results demonstrate that Sm-substituted BifeO3 films have potential for application in low voltage operational device.

Enhanced Electric and Magnetic Properties of the Epitaxial $({\rm Ba}_{0.5}{\rm Sr}_{0.5}){\rm TiO}_{3}/{\rm BiFeO}_{3}$ Multiferroic Heterostructure

Multiferroic heterostructure (Ba0.5Sr0.5)TiO3(BST)/BiFeO3(BFO) have been deposited by pulsed laser deposition method. X-ray diffraction shows that the BFO and BST were epitaxial grown on La0.7Sr0.3MnO3-buffered (100) SrTiO3 substrate. Interestingly, the BST/BFO heterostructure exhibits improved ferroelectric and ferromagnetic behaviors with remnant polarization (2Pr) ~ 34.8 μC/cm2 and saturation magnetization (Ms) ~ 4.65 emu/cm3. Compared with the single BFO film, the BST/BFO heterostructure showed higher dielectric constant and lower dielectric loss. Furthermore, the leakage behaviors of the BST/BFO heterostructure were consistent with SCLC behavior at low electric-field region and PF emission at high electric-field region. Our result indicates the BST/BFO multiferroic heterostructure may be a promising material for the high-density memory application.

Yield stress analysis of 1D calcium and titanium precipitate-based giant electrorheological fluids

1D calcium and titanium composite nanorods synthesized were applied as electrorheological (ER) active materials with extremely high static yield stresses, i.e., giant ER effect. The yield stress of this giant ER fluid was analyzed using a new universal yield stress scaling equation in the form of the modified Bessel functions with two different limiting behaviors in a low and high electric field region. The universal yield stress equation collapsed the yield stress data onto a single curve.

Back-Side Readout Silicon Photomultiplier

We present a novel structure for the back-side readout silicon photomultipler (SiPM). Current SiPMs are front-illuminated structures with front-side readout, which have relatively small geometric fill factor leading to degradation in their photon detection efficiency (PDE). Back-side readout devices will provide an advantageous solution to achieve high PDE. We designed and investigated a novel structure that would allow back-side readout while creating a region of high electric field optimized for avalanche breakdown. In addition, this structure has relatively high fill factor and also allow direct coupling of individual micro-cell of the SiPM to application-specific integrated circuits. We will discuss the performance that can be attained with this structure through device simulation and the process flow that can be used to fabricate this structure through process simulation.

Stark effects of ZnO thin film and ZnO/ZnMgO quantum wells

AbstractWe have investigated external electric field dependent Stark effects of ZnO thin film and ZnO/ZnMgO QWs by electroreflectance (ER) spectroscopy to develop electroabsorption modulators. The ZnO single film and ZnO/ZnMgO QWs were grown by plasma‐assisted molecular beam epitaxy (PA‐MBE). ZnO single film exhibited red‐shift of 8 meV by applying external bias at 18 K. This red‐shift is due to Stark effect in a low electric field, but it was changed to Franz‐Keldysh effect in a high electric field region. We confirmed a large blue‐shift of 39 meV for ZnO/ZnMgO QWs by external bias at room temperature. This energy shift, originated from quantum confined Stark effect (QCSE) in ZnO/ZnMgO QWs, proved a large exciton binding energy of this system. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of floating-potential conductors on the electric field near overhead transmission lines

The use of helicopters as platforms equipped with infrared and UV detection, digital cameras and other inspection equipment is an effective method of increasing the efficiency and effectiveness of transmission line inspection. However, as a 'floating-potential conductor' near to a high-voltage transmission line, a helicopter causes distortion of the local electric field, with regions of high electric field near the helicopter's surface where the curvature is high. In this paper, these fields are investigated both by calculation and experimentally, using a simple metal sphere, and then a model of a helicopter, placed near to a short length of energized transmission line conductor.

Charge multiplication in irradiated segmented silicon detectors with special strip processing

Charge multiplication in severely irradiated silicon detectors is now a well proven effect that enhances their charge collection and makes them operable up to the doses anticipated for future super-colliders (like the high luminosity LHC at CERN). The effect is well documented but not completely understood. The multiplication is caused by impact ionisation due to hot electrons moving in the high electric field that develops near the junction in the irradiated sensors. The details of the electric field profile in the silicon bulk are not available due to the unknown spatial distribution of the inhomogeneous effective space charge in the hadron irradiated silicon bulk. The gradient of the effective space charge distribution is crucial for the formation of high electric field regions where the multiplication takes place. The electric field might be influenced by the implant forming the n–p junction and by a non-homogenous bulk space charge near the junction. Deep n+ structures (junction) could enhance or reduce the multiplication effect. Also an altered doping gradient (obtainable for example by a graded p-doping between the junction and the p-bulk) could achieve the same results. In order to achieve enhanced charge multiplication in microstrip detectors the junction has been shaped by mean of deep p-doping diffusion and of trenches etched in the silicon bulk and filled with n+ doped polysilicon to create a deep junction. We report here the result obtained with these methods before and after various doses of neutron irradiation.

Comparison of thermal and atomic-layer-deposited oxides on 4H-SiC after post-oxidation-annealing in nitric oxide

The electrical properties of thermally grown and atomic-layer-deposition (ALD) oxides, followed by nitridation treatment, on 4H-SiC substrate were compared. The nitridation treatment was performed with post oxidation annealing in NO atmosphere (NO POA). The best electrical characteristics of the thermally grown and ALD oxides were observed at 120 and 180 min NO POA, respectively. The NO POA treated ALD oxide showed extremely low interface trap density (Dit), less than 1011 eV−1 cm−1. A metal-oxide-semiconductor field-effect-transistor with the ALD oxide showed high field effect mobility, especially in the high electric field region. The reasons for these superior results were also discussed.

Field emission from ZnO whiskers under intervalley electron redistribution

ZnO field-emitter whiskers with nanometer diameter were fabricated by metal-organic chemical vapor deposition (MOCVD) growth on Si substrates. Their electron field emission properties and electron transfer effect between the valleys were investigated in a high vacuum chamber. The Fowler–Nordheim (F–N) plots of the emission current show different slopes for the small and high electric field regions. A model based on the electron-emission from valleys having different specific electron affinities is proposed to explain the experimental results. The paper presents a study of the conduction band of nano-structured ZnO with the help of field emission experiments. The energy difference between the lower and upper valleys was determined to be between 3.02eV and 3.3eV. The effective work function from the satellite valley is much lower than from the Γ-valley. These results can explain the usually obtained large discrepancies between extremely high field enhancement factors by fitting using F–N equation with known work function Φ from the Γ-valley and the geometrical estimated field enhancement factors for ZnO emitter. These functional field emitters based on ZnO materials and their ternaries can also be used as ultraviolet photodetector and find new applications for miniaturized photo-field assisted vacuum devices.

Investigation of transport behavior in Ba doped BiFeO3

Bi1−xBaxFeO3 (x=0.00–0.25) samples were prepared by conventional solid state reaction method. X-ray diffraction revealed the rhombohedrally distorted perovskite structure for undoped BiFeO3 with a phase transition from rhombohedral to pseudo cubic on Ba substitution. The leakage current density of 10% Ba substituted sample is found to be four orders of magnitude less than that of the pure BiFeO3. Grain boundary limited conduction and space charge limited conduction mechanisms are involved in low and high electric field regions respectively for all the samples except 10% Ba doped BFeO3 which obeys grain boundary limited conduction mechanism in whole of the electric field range. Dielectric measurements showed that the dielectric constant and dielectric loss attained their minimum values at 10% Ba substitution. Thus 10% Ba is found to be optimum concentration to have better multiferroic properties. Undoped BiFeO3 and 5% Ba doped samples have very large values of dielectric constants and leakage current densities which can be attributed to a large number of oxygen vacancies in these samples, indicating an extrinsic response of these compositions.

Effect of contact resistance on field emission from carbon nanotube

After accounting for a contact resistance between carbon nanotube (CNT) and substrate, the local electric filed of top of CNT were calculated by combining an improved floated sphere model and the Fowler-Nordheim theory for understand the effect of the contact resistance on field emission from CNT. It is found that the field emission current is limited and current saturation and nonlinear characteristics of the Fowler-Nordheim plots are produced by the contact resistance in region of high electric field. The origin can be attributed to the local electric filed of top of CNT remarkably debases as compared to without the contact resistance.

An array of interdigitated parallel wire electrodes for preparing a large-scale nanocomposite film with aligned carbon nanotubes

Application of high electric field is effective for the alignment of carbon nanotube (CNT) in a nanocomposite film. The conventionally used single pair of parallel plate electrodes is not applicable to large-sized nanocomposite fabrication due to limited output voltage of the high-voltage source. We have proposed an array of parallel wire electrodes to address this issue. The composite material was spread over a thin dielectric layer placed on the wire electrodes. The high electric field region can be extended over a wider area just by increasing the number of electrode pairs. Discrete electric field distribution bordered by the wire electrodes was avoided by linearly oscillated motion of the composite film. A CNT/epoxy resin composite film with a size of 15 cm × 15 cm was successfully fabricated.

Multiferroic Properties and Leakage Current Mechanisms of ${\rm Bi}_{0.9}{\rm Eu}_{0.1}{\rm FeO}_{3}$ Thin Films

Bi0.9Eu0.1FeO3 (BEFO) thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates using the sol-gel method and rapid thermal annealing in an oxygen atmosphere. The effects of annealing temperature (400 ~ 700 C) on microstructure and multiferroic properties of thin films were investigated. The X-ray diffraction analysis showed that the BEFO thin films had an orthorhombic structure. The thin films showed ferroelectric and ferromagnetic properties with remanent polarization (2Pr) of 15 μC/cm2 and remnant magnetization (2Mr) of 4.2 emu/g. The leakage current density (J) of the BEFO thin film annealed at 700 °C was 4.25t10-8& A/cm2 at 150 kV/cm. The leakage current was affected not only by the microstructure but also by the interface between the Pt electrode and the BEFO thin films. Moreover, it was found that more than one conduction mechanism was involved in the electric field range used in these experiments. In the low electric field region, the leakage current was controlled by Poole-Frenkel emission. However, the mechanism could be explained by Schottky emission from the Pt electrode in the high electric field region.

A handheld preconcentrator for the rapid collection of cancerous cells using dielectrophoresis generated by circular microelectrodes in stepping electric fields

The ability to concentrate biological cells, such as circulating tumor cells, circulating fetal cells, and stem cells, is an important issue in medical diagnostics and characterization. The present study develops a handheld device capable of effectively preconcentrating cancerous cells. Circular microelectrodes were designed to generate a stepping electric field by switching the electric field to an adjacent electrode pair by relays. Cancerous cells with a positive dielectrophoretic response are guided toward the center of the circular microelectrodes due to the region of high electric field between the adjacent electrodes being gradually decreased in the direction of the stepping electric field. Numerical simulations of the electric fields were performed to demonstrate the concept of the proposed design. The preconcentration of HeLa cells, which are a human cervical carcinoma cell line, was achieved in 160 s with an efficiency of around 76%, with an applied peak-to-peak voltage of 16 V at a frequency of 1 MHz.

Valence-driven electrical behavior of manganese-modified bismuth ferrite thin films

BiFe0.95R0.05O3 (Mn2+, Mn3+, and Mn4+) thin films with (110) orientation were fabricated on SrRuO3/Pt/TiO2/SiO2/Si(100) substrates via rf sputtering. With the increasing valence of Mn in BiFe0.95R0.05O3, the concentration of Fe2+ increases, whereas the concentration of oxygen vacancies decreases. The electrical properties of BiFe0.95R0.05O3 are correlated with the valence of Mn. Their leakage current density is dependent on the concentration of oxygen vacancies caused by different valences of Mn. Their P-E loops become better with the increasing valence of Mn owing to a lower leakage current density in high electric field regions, and a large remanent polarization of 2Pr ∼ 145.2 μC/cm2 is obtained for the Mn4+-doped film. For the Mn2+-doped bismuth ferrite film, the space-charge-limited conduction and Schottky barrier dominate its leakage behavior under a negative electric field, the Ohmic conduction and Schottky barrier are involved in the leakage behavior under a positive electric field, and the interface-limited Fowler–Nordheim tunneling is their dominant mechanism in a high electric field region. In contrast, an Ohmic conduction dominates the leakage behavior of Mn3+- and Mn4+-doped films regardless of negative and positive directions or measurement temperatures.

Leakage mechanism of cation -modified BiFeO3 thin film

To investigate the leakage mechanisms in cation -substituted BiFeO3 (BFO) thin films, in Bi site or Fe site or both sites, Bi0.92La0.08FeO3, BiFe0.95Mn0.05O3, and Bi0.92La0.08Fe0.95Mn0.05O3 thin films were grown in situ by radio frequency magnetic sputtering on SrRuO3/SrTiO3(111) substrates, where the (111) orientation is established in all thin films. The variation in cation substitution results in different leakage behavior of BFO thin films. Space charge limited conduction and a grain boundary limited behavior are responsible for the leakage behavior of Bi0.92La0.08FeO3 and BiFe0.95Mn0.05O3 thin films in a low electric field region, respectively, while an interface-limited Fowler-Nordheim tunneling is involved in their leakage behavior in a high electric field region. In contrast, the leakage of Bi0.92La0.08Fe0.95Mn0.05O3 endures a transition from an Ohmic conduction to space charge limited conduction with increasing electric fields. The three thin films however show little temperature dependence of the leakage behavior in the temperature range investigated.