Threshold Electric Field Research Articles

Experimental Generation of 1.1-kA Gyrating Electron Beam Current From an Explosive Emission Cathode Magnetron Injection Gun

Most high-power gyrotrons are driven by the thermal cathodes, and the output power can only reach megawatt (MW) level. In the present study, a single anode explosive emission cathode (EEC) magnetron injection gun (MIG) with the high beam current, the pitch radio of 1.2 and the controlled beam velocity spread was designed. At the peak voltage of 300 kV, the peak beam current of 1.1 kA and pulsewidth of 170 ns were emitted by a carbon fiber array (CFA) emitter. Compared to the reported EEC MIG, large beam loss was avoided in this experiment. The guiding center radius of 14.1 mm was close to the simulation results. CFA has the stronger emission capability, the lower emission threshold electric field, and the better emission uniformity than sharpened edge graphite (SEG), so it is suggested as the emitter of the EEC MIG.

Toward an Integrated View of Ionospheric Plasma Instabilities: 6. Analytic Analysis of Thermal Effects

AbstractThermal effects in the ionospheric plasma instabilities including the Farley‐Buneman instability (FBI), the gradient‐drift instability (GDI), and the ion‐thermal instability (ITI) are analyzed, focusing on analytic analysis of the previously obtained general expression of the combined instability growth rate. It is shown that thermal effects lead to generally nonmonotonic behavior of the growth rate with the background electric field or, equivalently with the plasma drift speed , in contrast with the conventional quadratic (FBI) or linear (GDI) dependence. The threshold electric field for FBI is demonstrated to exist at all altitudes, although at higher altitudes and/or at longer wavelength the threshold fields become too high to be observed in the ionosphere. The GDI growth rate is shown to be significantly modified by the thermal effects at long wavelengths. In the absence of thermal effects, the growth rate is proportional to a cosine of the flow angle, the angle between the differential plasma drift and the wavevector. Thermal effects result in an additional phase shift that maximizes at an altitude around 120 km, using representative high‐latitude ionospheric parameters, and in an increase in the proportionality coefficient by up to a factor of 2. The study highlights the usefulness of an analytic treatment for revealing additional insights into the instability behavior in the broad range of ionospheric parameters that may remain hidden using only numerical treatment.

Multichannel Depletion-Type Field-Effect Transistor Based on Ferromagnetic Germanene

Based on ferromagnetic germanene, we theoretically propose a multichannel depletion-type field-effect transistor (FET) operated by a vertical electric field. The electron transport properties of the topological transistor are investigated through the nonequilibrium Green's function method. The results reveal that new edge channels can be formed by removing some $\mathrm{Ge}$ atoms along the $x$ axis of the device. The proposed multichannel ferromagnetic germanene transistor has a twice on-state current and half subthreshold swing than that of traditional germanene FETs. Under the coaction of electric induced staggered potential and staggered exchange field, both the $100\mathrm{%}$ spin-polarized edge states and valleys can be achieved. The ferromagnetic germanene FET can be turned off just by adjusting the electric field. In the low electric field conditions, the switching-off mechanism is due to spin blocking caused by the edge-state mismatch, while for relatively high electric field cases, both the edge-state mismatch and energy-valley mismatch are utilized. With the moderate increase in the exchange field, the switching mechanism is not changed, but the threshold electric field and breakdown voltage of the FET can be, respectively, reduced and enhanced significantly. All the results indicate that the proposed ferromagnetic germanene FET is a promising candidate for ultra-low-power dissipation topological devices.

Electrokinetic instability due to streamwise conductivity gradients in microchip electrophoresis

We present an experimental and numerical investigation of electrokinetic instability (EKI) in microchannel flow with streamwise conductivity gradients, such as those observed during sample stacking in capillary electrophoresis. A plug of a low-conductivity electrolyte solution is initially sandwiched between two high-conductivity zones in a microchannel. This spatial conductivity gradient is subjected to an external electric field applied along the microchannel axis, and for sufficiently strong electric fields an instability sets in. We have explored the physics of this EKI through experiments and numerical simulations, and supplemented the results using scaling analysis. We performed EKI experiments at different electric field values and visualised the flow using a passive fluorescent tracer. The experimental data were analysed using the proper orthogonal decomposition technique to obtain a quantitative measure of the threshold electric field for the onset of instability, along with the corresponding coherent structures. To elucidate the physical mechanism underlying the instability, we performed high-resolution numerical simulations of ion transport coupled with fluid flow driven by the electric body force. Simulations reveal that the non-uniform electroosmotic flow due to axially varying conductivity field causes a recirculating flow within the low-conductivity region, and creates a new configuration wherein the local conductivity gradients are orthogonal to the applied electric field. This configuration leads to EKI above a threshold electric field. The spatial features of the instability predicted by the simulations and the threshold electric field are in good agreement with the experimental observations and provide useful insight into the underlying mechanism of instability.

A probabilistic transcranial magnetic stimulation localization method

Objective. Transcranial magnetic stimulation (TMS) can be used to safely and noninvasively activate brain tissue. However, the characteristic parameters of the neuronal activation have been largely unclear. In this work, we propose a novel neuronal activation model and develop a method to infer its parameters from measured motor evoked potential signals. Approach. The connection between neuronal activation due to an induced electric field and a measured motor threshold is modeled. The posterior distribution of the model parameters are inferred from measurement data using Bayes’ formula. The measurements are the active motor thresholds obtained with multiple stimulating coil locations, and the parameters of the model are the location, preferred direction of activation, and threshold electric field value of the activation site. The posterior distribution is sampled using a Markov chain Monte Carlo method. We quantify the plausibility of the model by calculating the marginal likelihood of the measured thresholds. The method is validated with synthetic data and applied to motor threshold measurements from the first dorsal interosseus muscle in five healthy participants. Main results. The method produces a probability distribution for the activation location, from which a minimal volume where the activation occurs with 95% probability can be derived. For eight or nine stimulating coil locations, the smallest such a volume obtained was approximately 100 mm3. The 95% probability volume intersected the pre-central gyral crown and the anterior wall of the central sulcus, and the preferred direction was perpendicular to the central sulcus, both findings being consistent with the literature. Furthermore, it was not possible to rule out if the activation occurred either in the white or grey matter. In one participant, two distinct activations sites were found while others exhibited a unique site. Significance. The method is both generic and robust, and it lays a foundation for a framework that enables accurate analysis and characterization of TMS activation mechanisms.

Unveiling the Nottingham Inversion Instability during the thermo-field emission from refractory metal micro-protrusions

The electron emission by micro-protrusions has been studied for over a century, but the complete explanation of the unstable behaviors and their origin remains an open issue. These systems often evolve towards vacuum breakdown, which makes experimental studies of instabilities very difficult. Modeling studies are therefore necessary. In our model, refractory metals have shown the most striking results for discontinuities or jumps recorded on the electron emitted current under high applied voltages. Herein, we provide evidence on the mechanisms responsible for the initiation of a thermal instability during the field emission from refractory metal micro-protrusions. A jump in the emission current at steady state is found beyond a threshold electric field, and it is correlated to a similar jump in temperature. These jumps are related to a transient runaway of the resistive heating that occurs after the Nottingham flux inversion. That causes the hottest region to move beneath the apex, and generates an emerging heat reflux towards the emitting surface. Two additional conditions are required to initiate the runaway. The emitter geometry must ensure a large emission area and the thermal conductivity must be high enough at high temperatures so that the heat reflux can significantly compete with the heat diffusion towards the thermostat. The whole phenomenon, that we propose to call the Nottingham Inversion Instability, can explain unexpected thermal failures and breakdowns observed with field emitters.

A new class of ion substitution to achieve high electrostrain under low electric field in BNT‐based ceramics

AbstractFor Bi0.5Na0.5TiO3 (BNT)‐based materials, the effective way of composition modification to solve the drawback of considerable remanent strain (Srem) and achieve high electrostrain appeals intensive research interest, which often accompanies by a high electric field threshold to trigger the transition from ergodic relaxor (ER) state to ferroelectric (FE) state. Here, a unipolar electrostrain of 0.40% with the high normalized strain d33*(=Smax/Emax) of 793 pm/V under a low electric field of 5 kV/mm is firstly reported in rare‐earth Ce‐modified 0.935Bi0.5Na0.5TiO3–0.065BaTiO3 ceramics. Through the A‐ and B‐sites substitution with donor characteristic of multivalent Ce ion, two modification effects (i.e., compositional disorder and A‐site vacancy) are induced to weaken the A–O bonds and break the long‐range order. Microscopically, the proportion among three coexisted space groups (R3c, P4mm, and P4bm) changes in an opposite law when Ce concentration or poling electric field is served as variable, respectively. The domain size degrades after doping, but there still coexist small‐sized polar regions and labyrinth‐type domains in the optimal compound, wherein better reversibility is proved compared with undoped specimen from writing domain mode. As a result, the good reversibility and low electric field threshold (i.e., low‐energy barrier) to integrate relaxor state into FE state are ascribed to the coexistence of three phases and the coexistence of small‐sized polar regions and labyrinth‐type domains. This work not only enlarges the class of ion substitution other than the familiar substitution ions to achieve high electrostrain but also supplies a simple and propagable way to improve the relatively high electric field threshold through understanding the intrinsic mechanism of Ce ion.

Low threshold optical bistability in graphene/waveguide hybrid structure at terahertz frequencies

Here we propose a planar graphene/dielectric multilayer configuration to realize low threshold optical bistability at terahertz frequencies. This low-threshold optical bistability is achieved by field enhancement owing to the couple of the surface plasmon polaritons and the planar waveguide mode. We discussed the influence of graphene sheets and planar waveguide mode on the hysteretic response of the TM-polarization reflected light. It is found that the switch-up and switch-down threshold electric fields required to observe the optical bistable behavior are affected markedly by the excitation of surface plasmon polaritons or planar waveguide mode. Besides, the switching threshold value can be further reduced by coupling the surface plasmon polaritons and planar waveguide mode, hence providing a way of realizing low threshold and tunable optical bistable devices.

Impact of bio-target location and their fill-in factor on the sensitivity of hetero channel double gate MOSFET label-free biosensor

In this work, the performance of dielectric modulated InP/InGaAs/InP based on the hetero channel dual material double gate MOSFET (DM-H-DMDG MOSFET) for the label-free electrical identification of bio-targets has been inspected with the help of a 2D TCAD device simulator. The impact of bio-target’s location and their fill factor position has been analysed to observe the device sensitivity. Under the dry situation, the effect of charged and non-charged biomolecules on the electrical features such as threshold voltage, electric field, drain current, subthreshold performance, and sensitivity of DM-H-DMDG MOSFET has been evaluated. Simulation results show that the threshold voltage sensitivity of the proposed device is 0.62 and 0.59 when the fill factor is 100% and 50% respectively. The peak value of an electric field is 4.2 × 106 V cm−1 and 4.5 × 106 V cm−1 respectively near the source end and 0.5 × 105 V cm−1 and 5.5 × 105 V cm−1 near the drain end, when positively/negatively charged biomolecules are immobilised in the cavity. Again, the threshold voltage of the device is obtained as 0.265 V/0.245 V when the fill factor is 100% and 50% respectively.

Distinctive features of the charge density wave collective motion driven by Hall electric field in NbSe3

We present a comparative study of the charge density wave (CDW) sliding at low temperatures in NbSe3 between two configurations: the conventional one with the current applied along the chain axis and that, the CDW being driven by the Hall electric field, with the current applied along micrometer-sized bridge-type structures cut perpendicular to the chain axis. In this Hall bar configuration, nonlinear properties can be easily extended to much lower temperatures. The threshold electric field, Et, for CDW depinning is very sharp and has been measured down to 0.1 mK. It is found that Et becomes temperature independent below T≈4.2 K, which suggests a crossover from thermal fluctuations to a tunneling mechanism for CDW depinning.

Quantum fluidic charge density wave transport

We discuss charge density wave transport as the periodic flow of a quantum fluid of electron–phonon correlates, viewed as quantum solitons, within the condensate. Pair creation of charged soliton droplets is prevented by their electrostatic energy below a Coulomb-blockade threshold electric field. Above threshold, the quantum fluid flows in drip-like fashion as microscopic entities tunnel coherently from one charging energy macrostate to the next. We summarize the time-correlated soliton tunneling model and compare simulations of coherent oscillations, narrow band noise, and current–voltage characteristics with experiment. We also explore the possibility of collective quantum behavior at room temperature in some materials. Finally, we discuss potential applications in quantum information processing.

Retrospective Study for Validation and Improvement of Numerical Treatment Planning of Irreversible Electroporation Ablation for Treatment of Liver Tumors.

The aims of this study were to determine the electric field threshold that best fits the local response to irreversible electroporation (IRE) ablation of hepatic tumors as seen in follow-up MRI; to numerically evaluate the heat generating effect of IRE; and to demonstrate the utility of treatment planning to improve procedures in the future. 18 cases of hepatic tumors treated with IRE ablation were numerically reconstructed and treatment outcome was computed with a numerical treatment planning framework. Simulated ablation volumes were compared to ablation volumes segmented from 6-week follow-up MRI. Two cases with a high thermal component were selected for numerical optimization. The best fit between segmented and simulated ablation zones was obtained at 900 V/cm threshold with the average absolute error of 5.6 ± 1.5 mm. Considerable heating was observed in 7/18 cases, where >50% of tumor volume experienced heating likely to cause thermal damage. In the selected two cases, thermal damage was eliminated with adjustment of applied voltages. Lesions visible on MRI 6 weeks post IRE represent areas that experienced an electric field of 900 V/cm or higher. This threshold is higher than previously reported for IRE of hepatic tumors. It is likely the 6-week follow-up period was too long and the ablation zone has already shrunk considerably, resulting in overestimation of the threshold. We developed a sophisticated method for validation of the numerical treatment planning framework. A future prospective study can be effectively designed based on the findings of this study.

Charge trapping and recovery in ALD HfO2/β-Ga2O3 (010) MOS capacitors

The reliability of atomic layer deposited HfO2 β-Ga2O3 (010) MOS capacitors (MOSCAPs) was tested using constant voltage stress measurements. The HfO2/β-Ga2O3 MOSCAPs showed significant positive flatband voltage shifts (ΔV fb) of up to +1.3 V after 4.3 × 103 s stress, likely due to electron trapping in the dielectric in border traps. Results indicate there may exist an electric field threshold between 0.98 and 1.23 MV cm−1 for electron trapping to occur in these MOSCAPs. Deep ultra-violet (DUV) illumination enables full recovery from the charge trapping. In contrast, HfO2/Si MOSCAPs do not recover under DUV illumination and exhibit smaller voltage shifts upon initial testing. We thus surmise that the type-II band alignment between HfO2 and β-Ga2O3 enables full recovery from stress-induced charge trapping via photogeneration of electron–hole pairs and hole transport across the negative valence band offset. This hypothesis is borne out by the observation of photo-current in the HfO2/β-Ga2O3 MOSCAPs when biased in depletion. In sum, HfO2/β-Ga2O3 MOS structures appear to be susceptible to flatband voltage shifts during stress bias due to the availability and accessibility of border traps. This work highlights the unique challenges in forming reliable ultra-wide band gap MOS devices, due to the significant role that border traps in the lower half of the insulator band gap play in bias stress response.

Dosimetry Analysis in Non-brain Tissues During TMS Exposure of Broca's and M1 Areas.

For human protection, the internal electric field is used as a dosimetric quantity for electromagnetic fields lower than 5–10 MHz. According to international standards, in this frequency range, electrostimulation is the main adverse effect against which protection is needed. One of the topics to be investigated is the quantification of the internal electric field threshold levels of perception and pain. Pain has been reported as a side effect during transcranial magnetic stimulation (TMS), especially during stimulation of the Broca’s (speech) area of the brain. In this study, we designed an experiment to conduct a dosimetry analysis to quantify the internal electric field corresponding to perception and pain thresholds when targeting the Broca’s and M1 areas from magnetic stimulator exposure. Dosimetry analysis was conducted using a multi-scale analysis in an individualized head model to investigate electrostimulation in an axonal model. The main finding is that the stimulation on the primary motor cortex has higher perception and pain thresholds when compared to Broca’s area. Also, TMS-induced electric field applied to Broca’s area exhibited dependence on the coil orientation at lower electric field threshold which was found to be related to the location and thickness of pain fibers. The derived dosimetry quantities provide a scientific rationale for the development of human protection guidelines and the estimation of possible side effects of magnetic stimulation in clinical applications.

Preparation of silver nanoparticles on carbon nanotubes via photothermal heating and their field emission characteristics

Silver (Ag) nanoparticles decorated on carbon nanotubes (CNTs) were rapidly formed by the photothermal heating provided by infrared (IR) irradiation. The method was implemented without any solvent, reductants and applied current. By optimizing the amount of precursors and photothermal heating time, the size of the silver nanoparticles could also be controlled. After decoration of the silver nanoparticles on carbon nanotubes, the field emission characteristics were noted to be enhanced, while the turn-on electric field (at the current density of 10 μA/cm2) and threshold electric field (at the current density of 1 mA/cm2) decreased. At 10% mol Ag loading, the current did not exhibit decay for four hours at the current density of 1 mA/cm2.

The influence of Mn doping on the leakage current mechanisms and resistance degradation behavior in lead zirconate titanate films

The electrical reliability of lead zirconate titanate (PZT) films was improved by incorporating Mn; the time dependent dielectric breakdown lifetimes and the associated activation energy both remarkably increased with Mn concentration. The correlation between the defect chemistry and the resistance degradation was studied to understand the physical mechanism(s) responsible for enhanced electrical reliability. At lower electric fields, Poole-Frenkel emission was responsible for the leakage current. Beyond a threshold electric field, Schottky emission controlled the leakage. After electrical degradation of a 2 mol.% Mn doped PZT film, no significant change in potential barrier height for injecting electrons from the cathode into the anode was observed. This suggests that the degradation is mostly controlled by Poole-Frenkel conduction via some combination of hole migration between lead vacancies, small polaron hopping between Mn sites, and hole hopping between Pb2+ and Pb3+. No variation in the valence state of Ti near the cathode was observed in degraded Mn doped PZT films, implying that multivalent Mn provides trap sites for electrons and holes; free electron generation due to compensation of oxygen vacancies at the cathode and free hole formation at the anode region might be suppressed by the valence changes from Mn3+ to Mn2+ and Mn2+ to Mn3+ respectively.

Electrical Unfolding of Cytochrome C During Translocation through a Nanopore Constriction

Many small proteins move across cellular compartments through narrow pores. In order to thread a protein through a constriction, free energy must be overcome to either deform or completely unfold the protein. In principle, the diameter of the pore, along with the effective driving force of transport, should be critical factors that govern whether protein translocation proceeds via squeezing, unfolding/threading, or both. To directly probe this, we studied the electric-field-driven translocation behavior of cytochrome c (cyt c) through ultrathin silicon nitride (SiNx) solid-state nanopores of diameters ranging from 1.5 to 5.5 nm. For a 2.5 nm diameter pore we find that in a threshold electric field regime of ∼30-100 MV/m cyt c is able to squeeze into the pore. Further, as electric fields inside the pore further increase the unfolded state of cyt c is stabilized, facilitating translocation. In contrast, for 1.5 nm and 2 nm diameter pores, translocation occurs only by threading of the fully unfolded protein after it transitions through a higher energy unfolding intermediate state at the mouth of the pore. The transition energies between the metastable, intermediate, and unfolded protein states are extracted by exploiting differences in the state-dependent electric dipole interactions with the applied electric field. These experiments also map the various modes of protein translocation through a constriction, which opens new avenues for exploring protein folding structures, internal contacts, and electric field-induced deformability.

Implications of Nonlinear Material Parameters on the Dielectric Loss under Harmonic Distorted Voltages

The increasing number of power electronic devices in electrical grids may lead to harmonic distorted voltages, which are considered to be possible causes of component failures. In this study, the dielectric losses of epoxy polymer and functionally filled silicone rubber (f-SiR) samples are investigated under harmonic distorted voltages in terms of their dielectric losses and the consequent heat source density within the material. The results suggest that the epoxy polymer samples behave linearly to the electric field strength and therefore allow good predictability of the dielectric losses. The investigated f-SiR samples exhibit a nonlinear behaviour when an electric field threshold is exceeded. The subsequent direct loss measurements under harmonic distorted voltage reveal a sharp rise of the dielectric loss with increasing electrical field strength. This leads to a higher risk of excessive heat in the material when harmonics are present. In conclusion, the investigation highlights the difficulties of estimating dielectric losses in nonlinear dielectric materials when distorted voltages are present.

Field Electron Emission Experiments with Cold-Sprayed Cu-SiC Composite Coatings

Field electron emission of cold-sprayed copper-silicon carbide composite coating on a steel substrate was investigated. Two types of copper powders morphologies, namely dendritic and spherical, were mixed with crushed silicon carbide ceramic, and used as a feedstock. The powder mixtures were sprayed on the substrates and formed coatings with the designed surface topography—(i) flat and (ii) wavy. The microstructure of the coatings as well as the ceramic contents were analyzed. Initial tests proved that field emission from the Cu-SiC composite coatings was possible and depended mostly on the copper powder morphology. It was found out that the additional SiC layer deposited onto the composite coating significantly increased the number of electron emitters and thus improved the intensity of field emission. The Fowler–Nordheim model was used to find the threshold electric field, Eth, and coefficient of electric field amplification, β. These important properties of Cu/SiC + SiC coatings were found to be in the range of Eth = 20 to 24 V/µm and β = 340 to 410, respectively.

DC performance analysis of III–V/Si heterostructure double gate triple material PiN tunneling graphene nanoribbon FET circuits with quantum mechanical effects

In this article, the electrical behavior of laterally grown novel short-channel III–V/Si heterostructure double gate triple material PiN tunneling graphene nanoribbon field effect transistor (DG-TM-PiN-TGNFET) has been studied based on their quantum mechanical effect (QME). Firstly, by varying the device process parameters of the novel TFET structure, the DC parameter responses viz. threshold voltage, electric field and surface potential are investigated. Further these responses are analyzed by considering the QME for better device performance. Two-dimensional numerical device simulator (SILVACO TCAD) tool is used for simulating the quantum and semi-classical models. The simulation work has been validated by extensive analytical modeling, that reflected in our accurate graphical representations. Finally, to investigate the QME effect in circuit level applications, an TFET inverter circuit has been designed and its DC performance viz. power dissipation and propagation delay analysis is performed.