Threshold Electric Field Research Articles

Comparative study of electron field emission from randomly-oriented and vertically-aligned carbon nanotubes synthesized on stainless steel substrates

Randomly-oriented carbon nanotubes (CNTs) and vertically-aligned CNTs have been synthesized by a thermal chemical vapor deposition (CVD) process and a plasma enhanced CVD process, respectively, on stainless steel substrates without any external catalyst. Surface topography studies reveal that polishing and chemical etching result in favorable catalytic conditions for nucleation and growth of CNTs. Scanning electron microscopy and transmission electron microscopy observations reveal the growth of CNTs with catalyst particle at the tips. In comparison to randomly-oriented CNTs, vertically-aligned CNTs demonstrate better field emission properties with lower turn-on electric field of ∼2.0 V/μm, lower threshold electric field of ∼3.2 V/μm, and a 2.5-fold increase in the field enhancement factor. The vertical alignment of the emitters benefits the emission process by reducing the screening effect and streamlining the path of ejected electrons directly onto the anode. Vertically-aligned CNTs on conducting substrates are promising emitters in cold cathode vacuum electronics because of their direct contact with the substrate and efficient performance at low operating voltages.

Observation of field emission from carbon nanoparticles film coating on top of vertically aligned carbon nanotubes on silicon substrate

The carbon nanoparticles film coating on top of vertically aligned carbon nanotubes on silicon substrate (CNPs/CNTs/silicon) has been prepared by the pyrolysis of FePC at 960 °C. The surface morphologies and structure of the prepared sample are characterized by Scanning Electron Microscope, X-ray energy dispersive spectroscopy and Raman Spectroscopy. The field electron emission (FEE) properties of the CNPs/CNTs are also measured. A low turn-on electric field of 1.3 V/μm at a current density of 10 μA/cm2, low threshold electric field of 1.8 V/μm at a current density of 1 mA/cm2, a high emission density and good field emission stability are obtained. The above results make CNPs/CNTs/silicon an effective field emitter.

Polaron properties in pentathienoacene crystals

A two-dimensional tight-binding model is used to study static and dynamical properties of polarons in pentathienoacene crystals. Our computational approach determines the spacial parameter to obtain stable polarons in these materials by using a version of the Holstein–Peierls Hamiltonian. The model takes intra and intermolecular electron-lattice interactions into account. Remarkably, the results show that the charge transport mechanism is essentially one-dimensional in pentathienoacene crystals. This property is due to the nature of the polaron localization. Moreover, we show that the polaron dynamics can occur for an electric field threshold that overcomes the standard value of organic crystalline semiconductors.

Applicability analysis of the prevailing algorithms for reliable solution of the bipolar charge transport model

For space charge simulation inside the insulating materials as to characterize the dielectric performance, apart from accuracy of the equivalent physical and mathematical models themselves, corresponding algorithms to be adopted are also crucial for a reliable solution. However, no clear boundary has so far been defined regarding applicability of the prevailing algorithms. According to the injected charge density calculated by the Schottky law, it indicates the law is no longer applicable for the situation under low electric fields, for which cases a threshold electric field is proposed by the authors as the charge injection valve. Further, the algorithms commonly used are fully accounted for different cases. Numerical simulation of a specific waveform and the results based on symmetrical parameters are firstly used to verify the accuracy of the simulation process. A comparison based on dissymmetrical parameters demonstrates that, though the QUICKEST algorithm used for the convection equation presents good applicability while either the finite difference method (FDM) or the boundary element method (BEM) is used for the Poisson’s equation, the deviation between the two methods will enlarge with increased simulation time. According to the authors’ research, it is more appropriate to use BEM combined with the finite differential weighted essentially non-oscillatory (WENO) algorithm for a reliable solution. To elucidate the difference of the QUICKEST and the WENO algorithms, further computation below the threshold electric field is implemented, which indicates the QUICKEST algorithm is no longer applicable for long-term simulation. Hence, a preferable combination WENO + BEM presents the best choice for solving the bipolar charge transport model.

Holographic Description of Noncommutative Schwinger Effect

We consider the phenomenon of spontaneous pair production in the presence of an external electric field for noncommutative Yang-Mills theories. Using Maldacena’s holographic conjecture, the threshold electric field for pair production is computed from the quark/antiquark potential for noncommutative theories. As an effect of noncommutativity, the threshold electric field is seen to be smaller than its commutative counterpart. We also estimate the correction to the production rate of quark/antiquark pairs to the first order of the noncommutative deformation parameter. Our result bears resemblance with an earlier related work (based on field-theoretic methods).

Selective Inactivation of Pseudomonas aeruginosa and Staphylococcus epidermidis with Pulsed Electric Fields and Antibiotics.

Objective: Increasing numbers of multidrug-resistant bacteria make many antibiotics ineffective; therefore, new approaches to combat microbial infections are needed. In addition, antibiotics are not selective-they kill pathogenic organisms as well as organisms that could positively contribute to wound healing (bio flora). Approach: Here we report on selective inactivation of Pseudomonas aeruginosa and Staphylococcus epidermidis, potential pathogens involved in wound infections with pulsed electric fields (PEFs) and antibiotics (mix of penicillin, streptomycin, and nystatin). Results: Using a Taguchi experimental design in vitro, we found that, under similar electric field strengths, the pulse duration is the most important parameter for P. aeruginosa inactivation, followed by the number of pulses and pulse frequency. P. aeruginosa, a potential severe pathogen, is more sensitive than the less pathogenic S. epidermidis to PEF (alone or in combination with antibiotics). Applying 200 pulses with a duration of 60 μs at 2.8 Hz, the minimum electric fields of 308.8 ± 28.3 and 378.4 ± 12.9 V/mm were required to inactive P. aeruginosa and S. epidermidis, respectively. Addition of antibiotics reduced the threshold for minimum electric fields required to inactivate the bacteria. Innovation: This study provides essential information, such as critical electric field parameters for bacteria inactivation, required for developing in vivo treatment and clinical protocols for using PEF for wound healing. Conclusion: A combination of PEFs with antibiotics reduces the electric field threshold required for bacteria disinfection. Such an approach simplifies devices required to disinfect large areas of infected wounds.

Wide temperature range of an electrically tunable selective reflection of light by oblique helicoidal cholesteric

ABSTRACTOblique helicoidal cholesteric liquid crystals (ChOH) offer an unprecedented opportunity to tune selective reflection of light in a broad spectral range from ultraviolet to infrared by an electric field. The major problem is that the temperature range of stable ChOH is typically above the room temperature and is relatively narrow, a few degrees. In this work, we demonstrate that by using a mixture of flexible dimeric and rod-like molecules, one can significantly expand the temperature range of intense Bragg reflection, from 16°C to 27°C. We demonstrate that the selective reflection peak, reflection intensity, bandwidth and threshold electric field are all temperature dependent and discuss the associated mechanisms. The results show that both the electric field and temperature can be used to tune the structural colour of oblique helicoidal cholesteric structures. The proposed material can be used in switchable optical devices based on liquid crystals, such as light modulators, indoor smart windows, and filters.

First-principles study of a vertical spin switch in atomic scale two-dimensional platform

Abstract High in-plane charge carrier mobility and long spin diffusion length makes graphene a unique material for spin-based devices. However, in a vertical graphene junction, the 2pz orbitals of carbon atoms in graphene can be tuned via suitable magnetic substrates; this would affect the spin injection into graphene. Here, a vertical spin switch has been designed by embedding a single layer of graphene as a tunnel layer between the Ni (1 1 1) substrate. Periodic density functional approach in conjunction with Julliere’s model is used to calculate the tunnel magnetoresistance (TMR). Further, single-layered hexagonal Boron Nitride (h-BN) is sandwiched between the graphene and Ni (1 1 1) substrate to understand the role of hybridization at the interface on TMR. Our calculation shows that in contrast to the graphene junction, a much higher TMR value is obtainable in the case of the graphene/h-BN multi-tunnel junction (MTJ). The TMR in graphene junction is found to decrease with the increase of an externally applied electric field, and drops to zero for a field greater than equal to 0.16 V/A. Similar phenomenon was observed in the case of h-BN/graphene MTJ, where TMR value remains unchanged for electric field up to 0.1 V/A beyond which it drops to zero. The change in hybridization and charge-carrier-population at the interface modifies the magnetic exchange interaction and magnetic anisotropy resulting in a spin flip at interface, leads to rapid drop in TMR after a threshold electric field. The high and tunable TMR value suggests h-BN assisted high performance graphene based vertical spin switch.

Performance Analysis and Investigation of Subthreshold Short-Channel Behavior of a Dual-Material Elliptical Gate-All-Around MOSFET

The current investigation encompasses a detailed subthreshold short-channel performance analysis of a structure, namely a dual-material elliptical gate-all-around metal-oxide semiconductor field-effect transistor (DM EGAA MOSFET). This quasi-three-dimensional scaling length-based model features expression of central bottom potential from which parameters like threshold voltage and electric field have also been studied. The extent of immunity of the proposed device towards the different short-channel effects (SCEs) has also been studied. The analytical models are validated using ATLAS simulation data.

Space charge modelling in HVDC extruded cable insulation

With the growing interest in the development of HVDC cable technologies, the impact of space charge accumulation inside the polymeric insulation has attracted more attentions and the field distribution across the insulation has become the focus point of research. In this paper, several modifications have been applied on the bipolar charge transport model developed for the cable geometry. Based on many experimental observations, a threshold electric field at which the charge injection takes place was introduced. Considering the practical operation of HVDC cables, the thermal transient effects on space charge behaviors were particularly taken into account. A changing current flow has been applied in the core of a MV size cable, in order to further study the charge dynamics and to anticipate the field distribution within the insulation. The simulation results suggest that the thermal transient can affect the amount of injected charge and the charge movement significantly. The field inversion can only take place with higher temperature and larger temperature gradient, and this can be maintained even with temperature decreasing.

Analytical model development of channel potential, electric field, threshold voltage and drain current for gate workfunction engineered short channel E-mode N-polar GaN MOS-HEMT

In this paper an enhancement mode (E-mode) short channel N-polar GaN MOS-HEMT is proposed. In order to mitigate different short channel effects, workfunction engineering technique is applied to the gate electrode. An analytical model for channel potential, electric field threshold voltage and drain current is developed for the device and validated with Atlas TCAD simulation results. The variation of minimum channel potential and threshold voltage with respect to different channel lengths is also performed. It is observed that device with triple material gate shows better control of short channel effects as compared to single and double material gate based devices.

Numerical simulation modeling of the irreversible electroporation treatment zone for focal therapy of prostate cancer, correlation with whole-mount pathology and T2-weighted MRI sequences.

Background:At present, it is not possible to predict the ablation zone volume following irreversible electroporation (IRE) for prostate cancer (PCa). This study aimed to determine the necessary electrical field threshold to ablate human prostate tissue in vivo with IRE.Methods:In this prospective multicenter trial, patients with localized PCa were treated with IRE 4 weeks before their scheduled radical prostatectomy. In 13 patients, numerical models of the electrical field were generated and compared with the ablation zone volume on whole-mount pathology and T2-weighted magnetic resonance imaging (MRI) sequences. Volume-generating software was used to calculate the ablation zone volumes on histology and MRI. The electric field threshold to ablate prostate tissue was determined for each patient.Results:A total of 13 patients were included for histological and simulation analysis. The median electrical field threshold was 550 V/cm (interquartile range 383–750 V/cm) for the software-generated histology volumes. The median electrical field threshold was 500 V/cm (interquartile range 386–580 V/cm) when the ablation zone volumes were used from the follow-up MRI.Conclusions:The electrical field threshold to ablate human prostate tissue in vivo was determined using whole-mount pathology and MRI. These thresholds may be used to develop treatment planning or monitoring software for IRE prostate ablation; however, further optimization of simulation methods are required to decrease the variance that was observed between patients.

Effects of radial electric field on confinement of high energy particles in advanced fusion mirror reactor

The radial electric field Er in a magnetic confined machine, such as the compact fusion reactor (CFR), the field-reserved configuration (FRC), and the tokamak, plays an essential role in affecting the confinement properties of the high energy particles. The parallel velocities of the high energy particles will be accelerated or decelerated by applying a radial electric field, which could change the loss rate of the high energy particles in the magnetic confined machines. Unlike the fourth-order Runge-Kutta method RK4, the recently-developed Boris method can strictly preserve energy conservation of the high energy particles in the case without radial electric field. The orbit of high energy α particle in compact fusion reactor (CFR) is simulated by solving the equations of motion numerically with the Boris Algorithm. The effect of radial electric field on the orbit of the high energy α particle is investigated and the confinement of plasma in different radial electric fields in the CFR machine is studied in the present paper. By changing the strength of the radical electric field and the particles' radical locations in the middle plane of the CFR configuration, the confinement property of the high energy α particle is studied. The numerical results indicate that both the positive radial electric field and negative electric field can significantly affect the confinement of the high energy α particle. When the radial electric field is increased to a threshold, the high energy α particle could be confined in the central region of the CFR machine for a long enough time. The threshold of the radial electric field depends on the initial parameters of the confined particle. Systematic investigations of the radical electronic field effect will conduce to greatly improving the performance of the designed CFR machines.

Characterization of Ablation Thresholds for 3D-Cultured Patient-Derived Glioma Stem Cells in Response to High-Frequency Irreversible Electroporation.

High-frequency irreversible electroporation (H-FIRE) is a technique that uses pulsed electric fields that have been shown to ablate malignant cells. In order to evaluate the clinical potential of H-FIRE to treat glioblastoma (GBM), a primary brain tumor, we have studied the effects of high-frequency waveforms on therapy-resistant glioma stem-like cell (GSC) populations. We demonstrate that patient-derived GSCs are more susceptible to H-FIRE damage than primary normal astrocytes. This selectivity presents an opportunity for a degree of malignant cell targeting as bulk tumor cells and tumor stem cells are seen to exhibit similar lethal electric field thresholds, significantly lower than that of healthy astrocytes. However, neural stem cell (NSC) populations also exhibit a similar sensitivity to these pulses. This observation may suggest that different considerations be taken when applying these therapies in younger versus older patients, where the importance of preserving NSC populations may impose different restrictions on use. We also demonstrate variability in threshold among the three patient-derived GSC lines studied, suggesting the need for personalized cell-specific characterization in the development of potential clinical procedures. Future work may provide further useful insights regarding this patient-dependent variability observed that could inform targeted and personalized treatment.

Three-terminal memtransistors based on two-dimensional layered gallium selenide nanosheets for potential low-power electronics applications

A multi-terminal hybrid system named memtransistor has recently been proposed by combining the concepts of both memristor and field effect transistor (FET) with two-dimensional (2D) layered materials as the active semiconductor layer. In the memtransistors, the gate voltages are capable of modulating not only the transport properties of the fabricated FET, but also the resistive switching (RS) behaviors of the memristor. Herein, we employ mechanically exfoliated 2D layered GaSe nanosheets to prepare GaSe based three-terminal memtransistors. By using Ag as the electrodes, the memristor exhibits non-volatile bipolar RS characteristics. More importantly, under exposure to air for one week, the RS behaviors are dramatically enhanced with the ON/OFF ratio reaching up to 5.3 × 105 and ultralow threshold electric field of ~3.3 × 102 V cm−1. The ultralow threshold electric field of GaSe based memristor could be related to the low migration energy of the intrinsic Ga vacancy in p-type GaSe. Moreover, the GaSe-based memristor shows long-term retention (~104 s) and high cycling endurance (~5000 cycles) simultaneously. Hence, the fabricated three-terminal 2D GaSe memtransistors possess high performance with large switching ratios, ultralow threshold electric field, good endurance and long-term retention. Furthermore, the device demonstrates gate tunability in RS characteristics, suggesting the promising applications in multi-terminal electronic devices with low power consumption and complex functionalities, ranging from non-volatile memory, logic device to neuromorphic computing.

Analysis of NBTI Degradation in nMOS-Capacitors and nMOSFETs

This paper presents a new attempt to further understand negative bias temperature instability (NBTI) stress in semiconductor devices. NBTI impact has been experimentally investigated on both p-substrate MOS (nMOS-capacitor) and nMOS transistors under accumulation condition, and new findings have been revealed. Indeed, nMOS-capacitor’s flat band shift ( $\boldsymbol {\Delta }\text{V}_{\mathbf {FB}}$ ) under NBTI stress has disclosed that time exponent ( ${n}$ ) and activation energy ( ${\mathbf{E}}_{\mathbf{a}}$ ) do vary with applied voltage stress pointing out to the contribution of two components, interface ( $\text{N}_{\mathbf {IT}}$ ) and oxide ( $\text{N}_{\mathbf {OT}}$ ) traps. Besides, the threshold electric field delimiting NBTI and stress induced leakage current can be well established. These findings have been confirmed by the appearance of a turn-around effect in nMOS transistors under NBTI stress. Moreover, charge pumping characterization has unveiled that NBTI degradation in nMOS transistor goes through two stages. First, only $\text{N}_{\mathbf {IT}}$ is created, then simultaneous generation of $\text{N}_{\mathbf {IT}}$ and $\text{N}_{\mathbf {OT}}$ takes part.

Tracking Lysosome Migration within Chinese Hamster Ovary (CHO) Cells Following Exposure to Nanosecond Pulsed Electric Fields.

Above a threshold electric field strength, 600 ns-duration pulsed electric field (nsPEF) exposure substantially porates and permeabilizes cellular plasma membranes in aqueous solution to many small ions. Repetitive exposures increase permeabilization to calcium ions (Ca2+) in a dosage-dependent manner. Such exposure conditions can create relatively long-lived pores that reseal after passive lateral diffusion of lipids should have closed the pores. One explanation for eventual pore resealing is active membrane repair, and an ubiquitous repair mechanism in mammalian cells is lysosome exocytosis. A previous study shows that intracellular lysosome movement halts upon a 16.2 kV/cm, 600-ns PEF exposure of a single train of 20 pulses at 5 Hz. In that study, lysosome stagnation qualitatively correlates with the presence of Ca2+ in the extracellular solution and with microtubule collapse. The present study tests the hypothesis that limitation of nsPEF-induced Ca2+ influx and colloid osmotic cell swelling permits unabated lysosome translocation in exposed cells. The results indicate that the efforts used herein to preclude Ca2+ influx and colloid osmotic swelling following nsPEF exposure did not prevent attenuation of lysosome translocation. Intracellular lysosome movement is inhibited by nsPEF exposure(s) in the presence of PEG 300-containing solution or by 20 pulses of nsPEF in the presence of extracellular calcium. The only cases with no significant decreases in lysosome movement are the sham and exposure to a single nsPEF in Ca2+-free solution.

Density disturbance of small-scale field-aligned irregularities in the ionosphere heating experiments

A theoretical model which describes the small-scale irregularities excited by powerful high frequency (3–30 MHz) electromagnetic wave in ionosphere heating is investigated quantitatively in this paper. The model is based on the transport equation in magnetic plasma and mode conversion from electromagnetic wave to electrostatic wave in ionospheric modification. Threshold electric field for exciting small-scale (meter scale) irregularities and spatial spectra of irregularities are analytically calculated by this model. The results indicate that background electron density and geomagnetic field play an important role for the threshold electric field and the spatial scale of the electron density irregularities. The results demonstrate that the electric field threshold increases with the decrease of the spatial scale of the irregularities. For exciting meter scale irregularities, the threshold electric field is about tens of mV m−1. The theoretical results are consistent with those of the experiments.

Dynamics of positrons during relativistic electron runaway

Sufficiently strong electric fields in plasmas can accelerate charged particles to relativistic energies. In this paper we describe the dynamics of positrons accelerated in such electric fields, and calculate the fraction of created positrons that become runaway accelerated, along with the amount of radiation that they emit. We derive an analytical formula that shows the relative importance of the different positron production processes, and show that, above a certain threshold electric field, the pair production by photons is lower than that by collisions. We furthermore present analytical and numerical solutions to the positron kinetic equation; these are applied to calculate the fraction of positrons that become accelerated or thermalized, which enters into rate equations that describe the evolution of the density of the slow and fast positron populations. Finally, to indicate operational parameters required for positron detection during runaway in tokamak discharges, we give expressions for the parameter dependencies of detected annihilation radiation compared to bremsstrahlung detected at an angle perpendicular to the direction of runaway acceleration. Using the full leading-order pair-production cross-section, we demonstrate that previous related work has overestimated the collisional pair production by at least a factor of four.

Ablation outcome of irreversible electroporation on potato monitored by impedance spectrum under multi-electrode system

BackgroundIrreversible electroporation (IRE) therapy relies on pulsed electric fields to non-thermally ablate cancerous tissue. Methods for evaluating IRE ablation in situ are critical to assessing treatment outcome. Analyzing changes in tissue impedance caused by electroporation has been proposed as a method for quantifying IRE ablation. In this paper, we assess the hypothesis that irreversible electroporation ablation outcome can be monitored using the impedance change measured by the electrode pairs not in use, getting more information about the ablation size in different directions.MethodsUsing a square four-electrode configuration, the two diagonal electrodes were used to electroporate potato tissue. Next, the impedance changes, before and after treatment, were measured from different electrode pairs and the impedance information was extracted by fitting the data to an equivalent circuit model. Finally, we correlated the change of impedance from various electrode pairs to the ablation geometry through the use of fitted functions; then these functions were used to predict the ablation size and compared to the numerical simulation results.ResultsThe change in impedance from the electrodes used to apply pulses is larger and has higher deviation than the other electrode pairs. The ablation size and the change in resistance in the circuit model correlate with various linear functions. The coefficients of determination for the three functions are 0.8121, 0.8188 and 0.8691, respectively, showing satisfactory agreement. The functions can well predict the ablation size under different pulse numbers, and in some directions it did even better than the numerical simulation method, which used different electric field thresholds for different pulse numbers.ConclusionsThe relative change in tissue impedance measured from the non-energized electrodes can be used to assess ablation size during treatment with IRE according to linear functions.