Stages Of Breakdown Research Articles

Atomic-scale defects generated in the early/intermediate stages of dielectric breakdown in Si/SiO2 transistors

Electrically detected magnetic resonance and near-zero-field magnetoresistance measurements were used to study atomic-scale traps generated during high-field gate stressing in Si/SiO2 MOSFETs. The defects observed are almost certainly important to time-dependent dielectric breakdown. The measurements were made with spin-dependent recombination current involving defects at and near the Si/SiO2 boundary. The interface traps observed are Pb0 and Pb1 centers, which are silicon dangling bond defects. The ratio of Pb0/Pb1 is dependent on the gate stressing polarity. Electrically detected magnetic resonance measurements also reveal generation of E′ oxide defects near the Si/SiO2 interface. Near-zero-field magnetoresistance measurements made throughout stressing reveal that the local hyperfine environment of the interface traps changes with stressing time; these changes are almost certainly due to the redistribution of hydrogen near the interface.

Study of Drain Injected Breakdown Mechanisms in AlGaN/GaN-on-SiC HEMTs

Breakdown mechanism in 0.25- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mu } \text{m}$ </tex-math></inline-formula> gate length AlGaN/GaN-on-SiC iron doped high electron mobility transistors (HEMTs) with background carbon is investigated through the drain current injection technique. The measurement results reveal that it can be divided into two distinct stages according to the gate voltage levels. The first stage of the measured drain injected breakdown is mainly due to the initiation of the punchthrough process under the gate, and the second stage of breakdown is associated with the potential barrier between the unintentionally doped (UID) GaN and the Fe doped p-type GaN buffer layer which also has a higher carbon density. The electroluminescence (EL) results suggest that the first stage shows uniform punchthrough current flow, but localized leakage current flow associated with a snapback breakdown mechanism replaces the uniform punchthrough current flow and dominates the second stage. A 2D-TCAD simulation has been implemented and shows the current paths under uniform flow conditions.

Muzzle Arc Flow Field Simulation of a Small Caliber Launcher

Muzzle arc is a general phenomenon when the armature leaves the muzzle, and it is also a reason for the complexity of intermediate ballistic of electromagnetic launchers. In this article, a 3-D model has been developed to investigate muzzle arc flow field in a smaller caliber launcher. The coupled interaction of electromagnetic, flow, and thermal fields is realized by the magnetohydrodynamic (MHD) theory in conjunction with a renormalization group (RNG) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon $ </tex-math></inline-formula> turbulence model. The arc boundary conditions, arc root radius, and time-dependent current density are reasonably set on the basis of the experimental data and physical process. Simulation results reveal the relationship between muzzle arc and muzzle voltage. The rising edge of muzzle voltage corresponds to the arc expansion stage. The falling edge corresponds to the muzzle breakdown stage. And the turning point from rising edge to falling edge is the moment of muzzle breakdown. The flat section corresponds to the arc extinguishing stage. The muzzle blowback is the consequence of the arc expansion which produces a compression wave moving toward the breech. The velocity of blowback flow decreases from 670 to 270 m/s during the arc expansion stage. Then, it increases to about 350 m/s and tends to be stable due to the muzzle breakdown.

Fabrication of a Ceramic Foam Catalyst Using Polymer Foam Scrap via the Replica Technique for Dry Reforming.

Megapores with spherical-like cells connected through windows and high porosities make up catalyst supports in the form of ceramic foams. These characteristics provide significant benefits for catalytic processes that are limited by mass or heat transport. This study focuses on the manufacture of ceramic foam using a polymeric sponge replica process and polymer foams as a template for catalyst supports, which are industrial waste from the packaging sector. To make ceramic foam catalysts, they were dipped in a catalyst solution, followed by a breakdown stage and a sintering process. Experiments focused on determinants that affect the desired characteristics of ceramic foams, such as the types of polymer foams that affect foam morphology, the rheology of catalyst solution that affects catalyst dispersion, and the polymer decomposition rate that affects catalytic performance during dry reforming of the methane process. The cell architectures of polyurethane and polyvinyl alcohol foams are attractive for catalyst support preparation because they have 98–99% porosity and typical cell sizes of 200 and 50 μm, respectively. The polyurethane performance was superior to the performance of polyvinyl alcohol in terms of higher porosity and better catalytic-solution absorption offering high catalyst active areas. The catalyst prepared from concentrated 10 wt % Ni/Al2O3–MgO (10NAM) slurry had the highest surface area (59.18 m2/g) and the highest metal oxide dispersion (5.65%). These results are relevant to the flow behavior of catalyst slurry which plays a key role in coating the catalyst gel on the polymer template. The thermal decomposition rate used to remove the polymer template from the catalyst structure is proportional to the ceramic foam structure (catalyst support structure). The slow decomposition rate bent and fractured foam-cell struts more than the faster rate. On the other hand, achieving good catalyst dispersion on catalyst supports necessitated a high sintering rate. When sintering was adjusted at a high sintering rate, the metal–particle dispersion was relatively high, around 7.44%, and the surface area of ceramic foam catalysts was 64.61 m2/g. Finally, the catalytic behavior toward hydrogen production through the dry reforming of methane using a fixed-bed reactor was evaluated under certain operating conditions.

Volatile products formed during electrical breakdown of polyethylene terephthalate and polypropylene films in high vacuum

In this article we present the results of time-of-flight mass spectrometry of volatile products formed during the electrical breakdown of polyethylene terephthalate and polypropylene polymer films in high vacuum. During the breakdown of films, all the substance emitted from the breakdown channel is a gas of low-molecular products of destruction of macromolecules. The breakdown mass spectra do not contain lines of carbon molecules, the presence of which could indicate carbonation of the channel. To explain the formation of charge carriers, the ionization mechanism of destruction of macromolecules in an electric field is used without the involvement of impact ionization. The final stage of electrical breakdown (the flow of a high-density conduction current) occurs when the critical concentration of traps and electrons ~1024 m-3 is reached. Keywords: electrical breakdown, mass spectrometry, thermodestruction, ionization, macromolecule, trap.

Летучие продукты, образующиеся при электрическом пробое пленок полиэтилентерефталата и полипропилена в высоком вакууме

In this article we present the results of time-of-flight mass spectrometry of volatile products formed during the electrical breakdown of polyethylene terephthalate and polypropylene polymer films in high vacuum. During the breakdown of films, all the substance emitted from the breakdown channel is a gas of low-molecular products of destruction of macromolecules. The breakdown mass spectra do not contain lines of carbon molecules, the presence of which could indicate carbonation of the channel. To explain the formation of charge carriers, the ionization mechanism of destruction of macromolecules in an electric field is used without the involvement of impact ionization. The final stage of electrical breakdown (the flow of a high-density conduction current) occurs when the critical concentration of traps and electrons ≈ 10^24 1/m^3 is reached.

Modification of the cathode material around the explosive electron emission centers in the spark stage of vacuum breakdown

On the basis of numerical calculations estimates for the fields of mechanical stresses around the explosive electron emission centers of the cathode during the development of pulsed vacuum breakdown are given. Expansion of material due to conduction loss was taken into account. It is shown that the sizes of regions with broken crystalline structure is much larger than the corresponding of explosive emission centers. Keywords: vacuum breakdown, explosive electron emission, mechanical stresses.

Luminosity with large amplitude pulses after the initial breakdown stage in intracloud lightning flashes

Optical data are presented for two intracloud flashes in which there were five events having large amplitude, bipolar electric field change (E-change) pulses and strong VHF emissions. These bright events occurred 18.98–67.33 ms after the initiating event and 10–59 ms after the end of the initial breakdown stage. The three largest events were coincident with WorldWide Lightning Location Network detections of the sort previously associated with terrestrial gamma-ray flashes (TGFs); these pulses had range-normalized E-change amplitudes of 8.73, 8.33, and 3.81 V/m and estimated peak current magnitudes of 262, 250, and 114 kA. The other two events were 3.20 and 1.62 V/m (96 and 49 kA). All five events have bright enhanced luminosity (>10% above background) for durations of 0.7–1.20 ms, similar to durations of their moderate-to-strong VHF emissions. Full-frame peak intensities are factors of 1.82–4.46 times the background level. Maximum cumulative intensity in the camera frame occurs 84–98 μs after the E-change peak in three cases and ranges from −10 μs (before) to +115 μs (after) for all cases. Notably, in all five events the luminosity starts increasing when the E-change and VHF sensors begin detecting oscillations, 135–550 μs before the E-change peak. Pulse locations of each event extend through 3.6 to 4.3 km depth, starting below and ending above the altitude of flash initiation, and the linear path-length of activity with these events is estimated at 8.9–11.3 km within radar reflectivities of 20–40 dBZ. Although these events are not initial breakdown pulses, their luminosity could be visible from satellite-borne instruments and they may be associated with TGFs.

The effect of follicle size and cryoprotectants on nuclear maturation and early embryonic development of vitrified - thawed Awassi sheep oocytes (Ovis aries)

In this study, two experiments were conducted to study the effect of both the follicle size and the cryoprotectants dimethyl sulfoxide (DMSO) and ethylene glycol (EG) on the main phases of nuclear maturation (Experiment I), cleavage stages and embryo quality (Experiment II) of Awassi sheep oocytes. Follicles were classified into two groups: small follicles (SF) (1-2 mm) and large follicles (LF) (&gt; 2 mm). Oocytes were vitrified in three solutions: A (30% DMSO), B (30% EG) and C (15% DMSO and 15% EG). In Experiment I, the resulting vitrified-thawed oocytes in solution C achieved the best rates after the control group (fresh), respectively as the rates of maturation, germinal vesicle (GV), metaphase II(M-II), arrest, and lyses were 85.71% (P = 0.04), 8.33% (P = 0.02), 72.92% (P = 0.04); LF group, 15.25% (P = 0.04), and 5.08% (P = 0.04); SF group, respectively. In Experiment II, the same group of oocytes achieved the best rates after the control group, as the rates of fertilization, cleavage, 2-16 cell, Type3, blastocyst, and Type1 embryos were 63.28% (P = 0.001), 57.46% (P = 0.001), 40.38% (P = 0.04), 38.46% (P = 0.04); LF group, 30.00% (P = 0.01), and SF group 36.67% (P = 0.001), respectively, while the vitrified-thawed oocytes in A solution (SF group) reached the highest rate of Type 2 embryo quality (58.06%; P = 0.01). No significant differences were noticed in the germinal vesicle breakdown (GVBD), metaphase I (M-I) and morula stage. Vitrification of oocytes obtained from follicles with a diameter of more than 2 mm in a cocktail solution of DMSO (15%) and EG (15%) led to a significant increase in the yield and quality of the resulting sheep embryos.

New approach to breakdown equation in gases based on energy concept from inception stage to arc condition

In this paper, the proposed breakdown equation of gases based on energy concept is introduced from initiating stage to complete breakdown (arc) stage. In compounds, the chemical enthalpy represented in bonding energy may be used as a fundamental principle to determine the electrical breakdown voltage. The bond dissociation enthalpy of gaseous compounds indicates the minimum energy needed to release chemical compounds in the material. The breakdown equation based on energy concept is a governing equation and relates between the field of streamer inception E0 and the field in different discharge stages. These stages can be specified from the breakdown index (n) value. Under arc condition, the temperature inside the discharge trail of arc may be up to 19200K according to the proposed breakdown equation. At this temperature, n equal 64 and the field under arc condition Eb=8E0. At atmospheric pressure and 1cm distance electrode gap, the Eb has been calculated for air, N2, H2, and SF6 (36, 39, 18, 81.9kV/cm respectively). The results comprised in this research compare with experimental and analytical consequences.

Rural families’ thoughts about sexual development of their adolescents with neurodevelopmental disorders

The study aims to determine rural families’ experiences regarding sexual development of their adolescents with neurodevelopmental disorders. Thus, semi-structured interviews were conducted with 14 parents. Since the interviews included privacy issues, they were conducted one-to-one with the parents. The phenomenological method was used, depending on the research purpose. Inductive analysis was utilised in the analysis of the data obtained from the semi-structured interviews. Validity and reliability were included in all stages of data collection, breakdown and analysis. As a result, the families stated that their children exhibited inappropriate socio-sexual behaviours during adolescence; they strive to teach their children sexuality issues, although they do not know how and they generally prefer carrying their children along to prevent sexual abuse. Also, due to not knowing much about sexuality, they generally received their relatives’ support and requested comprehensive sexuality education (CSE) from special education teachers and other experts, especially about distinguishing good and bad people, menstruation and hiding sanitary pads. Although the literature reports that sexuality and its education are generally taboo, families in this study explained their thoughts on sexuality in full detail without tabooing. This makes the study different and meaningful, when compared to similar ones. The study was conducted in an eastern Turkey city with difficult access to special education. Thus, experts in rural areas are recommended to prepare and give necessary CSE programmes to families and individuals with special needs by conducting similar studies. These studies can be conducted not only with special education perspective but also in different disciplines. It is a basic human right for all individuals to receive CSE, thus as another recommendation, experts should give all children these courses in schools. &#x0D; &#x0D; Keywords: Comprehensive sexuality education, individuals with neurodevelopmental disorders, parenting education, phenomenological design.

Computational analysis of direct current breakdown process in SF6 at low pressure

The breakdown of SF6 gas at low pressure is of vital importance to both aerospace and microelectronics industries. However, the breakdown characteristics of SF6 in direct current at low pressure are still seldom studied. In this work, one-dimensional implicit particle-in-cell/Monte-Carlo collision algorithm is used to study the entire direct current breakdown process of low-pressure SF6. The ion-molecule collision, recombination, and external circuit are considered in the model. According to the results, the breakdown process can be divided into three stages: pre-breakdown stage, breakdown stage, and post-breakdown stage. In the pre-breakdown stage, the cathode sheath is not yet formed so the constant electric field exists in the entire area. In the breakdown stage, the formation mechanism of the cathode sheath is analyzed and the electrodes as a whole changes from capacitive to resistive, sharing the voltage with the external resistance. In the post-breakdown stage, the continued growth of positive ions leads to the formation of a thin anode sheath, which further causes the negative plasma potential, different from electropositive gas. The energy production terms including heating power and secondary electron emission (SEE) power are equal to the energy loss terms including collision loss power and boundary loss power, where collision loss power and boundary loss power are almost equal, while SEE power is negligible. In the final, plasma parameters gradually evolve to the last steady-state.

Compact Lightning Strokes in Winter Thunderstorms

AbstractWith the observation of a 14‐site Fast Antenna Lightning Mapping Array in the Hokuriku region of Japan, we identified a special type of lightning stroke called “compact stroke” in winter thunderstorms. A compact stroke starts with a fast downward negative leader followed by a “compact return stroke.” Compact strokes have the following characteristics that are not seen in normal lightning strokes: (a) Durations of preceding discharges (defined as the time difference between the return stroke and the start of the flash) are generally smaller than 200 μs. (b) Most compact strokes are inferred to be produced in small gaps between mountain tops and negative charge regions in winter thunderstorms. (c) Channel lengths of compact strokes are estimated to be shorter than 600 m with an average of about 300 m. (d) Characteristics of electric field change waveforms of compact return strokes are closely related with durations of preceding discharges. (e) Peak currents of compact return strokes increase with increasing channel lengths. It seems that elevations of mountain surfaces where compact strokes occur are comparable to the altitude of the lower positive charge region, so we speculate that the mountain surface and the near‐surface space carry positive charges when a storm is overhead and are virtually the lower positive charge region of a normal tripole structure. As a result, compact strokes are confined between the main negative and lower positive charge regions, and small pulses with short durations preceding compact return strokes are produced by downward negative leaders corresponding to the preliminary breakdown stage.

Local vortex line topology and geometry in turbulence

The local streamline topology classification method of Chong et al. (Phys. Fluids A: Fluid Dyn., vol. 2, no. 5, 1990, pp. 765–777) is adapted and extended to describe the geometry of infinitesimal vortex lines. Direct numerical simulation (DNS) data of forced isotropic turbulence reveals that the joint probability density function (p.d.f.) of the second ( $q_\omega$ ) and third ( $r_\omega$ ) normalized invariants of the vorticity gradient tensor asymptotes to a self-similar bell shape for $Re_\lambda &gt; 200$ . The same p.d.f. shape is also seen at the late stages of breakdown of a Taylor–Green vortex suggesting the universality of the bell-shaped p.d.f. form in turbulent flows. Additionally, vortex reconnection from different initial configurations is examined. The local topology and geometry of the reconnection bridge is shown to be nearly identical in all cases considered in this work. Overall, topological characterization of the vorticity field provides a useful analytical basis for examining vorticity dynamics in turbulence and other fluid flows.

Simulation of ionization-wave discharges: a direct comparison between the fluid model and E-FISH measurements

For a long period, there was a resolution gap between numerical modeling and experimental measurements, making it hard to conduct a direct comparison between them, but they are now developing in parallel. In this work, we numerically study diffusive ionization wave and fast ionization wave discharge experiments using recently published electric-field-induced second-harmonic (E-FISH) data together with a classical fluid model. We propose a pressure-E/N range for the drift diffusion approximation and a pressure-grid range for the local field/mean energy approximation of the fluid model. The three-term Helmholtz photoionization model is generalized using parameters given for N2, O2, CO2, and air. The capabilities of the classical fluid method for modeling the inception, propagation, and channel breakdown stages are studied. The calculated electric field evolution of the ionization is compared with E-FISH measurements in the discharge development and gap-closing stages. The influence of electrode shape and predefined electron density on the streamer morphology and the long-standing inception problem of the ionization waves are discussed in detail. Within the application range of the classical fluid model, good agreement can be achieved between calculation and measurement.

Effect of Gas-Mixture Ratio on the Characteristics of Positive DC Corona Discharge in SF6/N2 Gas Mixtures

The characteristics of positive DC corona discharge in SF6/N2 gas mixtures under different gas-mixture ratios are investigated with a needle-to-plane electrode configuration. With increasing applied voltage, a discharge-stage transition process including the Townsend stage, streamer-pulse stage, brush-pulse stage and breakdown stage is observed. The variation in current-pulse characteristics, including pulse-time parameters, mean pulse amplitude and pulse-repetition rate, is investigated under different gas-mixture ratios. The pulse-time parameters are not affected by gas-mixture ratio. The pulse-repetition rate increases with the increase of SF6 concentration and mean current, ranging from hundreds of kilohertz to thousands of kilohertz. The streamer-pulse amplitude increases with increasing SF6 concentration. With increasing mean current, the small-amplitude brush pulses become dominant, thus the mean pulse amplitude decreases. In order to further explore the influence mechanism of gas-mixture ratio on positive corona discharge, a fluid model of positive corona discharge is developed and relevant simulations show the formation process of current pulse, and verify the validity of the pulse characteristics changing with gas-mixture ratio.

Main modes of runaway electron generation during a breakdown of high-pressure gases in an inhomogeneous electric field

Using our recently proposed method, we have identified three modes of runaway electron generation. This method is based on the recording of a dynamic displacement current using a current collector. It makes it possible to unambiguously interpret the dynamics of ionization processes occurring at the stage of formation of a high-voltage nanosecond discharge in a strongly inhomogeneous electric field and dense gaseous media. Simultaneous and separate recording by the current collector of a runaway electron beam current and the dynamic displacement current as well as the recording of discharge characteristics and high-speed framing of plasma glow at the breakdown stage made it possible to interpret the runaway electron generation modes in terms of the rate of ionization processes. It has been shown how the reduced electric field strength, the gas kind, the design and material of a high-voltage cathode with a small radius of curvature, the amplitude and rise time of a voltage pulse as well as the delay in the onset of the explosive emission process at the cathode affect the implementation of one or another generation mode.

Simultaneous Observations of EIP, TGF, Elve, and Optical Lightning

AbstractOn February 8, 2019, the Atmosphere‐Space Interaction Monitor observed a terrestrial gamma‐ray flash (TGF) and an Elve from a positive intracloud (+IC) lightning during the initial breakdown stage of a lightning flash north east of Puerto Rico. A second Elve produced by the return stroke (RS) of a negative cloud‐to‐ground (−CG) lightning was observed 456 ms later about 300 km south of the first one. Radio measurements show that a short (30 μs) and large (280 kA km) energetic in‐cloud pulse (EIP) produced the electromagnetic (EM) wave for the first Elve while the RS of the −CG was the EM source for the second Elve. Assuming that the EIP and the RS were the sources of the 777 nm emissions, both the delay relative to the ultra‐violet pulse and the shape and duration of the 777 nm emissions can be explained by scattering and absorption inside the clouds. The TGF produced by the +IC lightning had the same duration as the EIP (∼30 μs). Due to the ±80 μs timing uncertainty of the TGF, we can only state that TGF was produced just before or most likely simultaneously with the EIP. The large 777 nm pulse indicates that a large part of the EIP was produced by a current flowing in a hot channel, but it is likely that the TGF current also contributed significantly to the EIP.

Research on the influence of the discharge breakdown process on the crater formation during EDM

PurposeThis paper aims to study the breakdown, oscillation and vanishing of the discharge channel and its influence on crater formation with simulation and experimental methods. The experiment results verified the effect of the oscillating characteristics of the discharge channel on the shape of the crater.Design/methodology/approachA mathematical model that considers the magnetohydrodynamics (MHD) and the discharge channel oscillation was established. The micro process of discharging based on magnetic-fluid coupling during electrical discharge machining (EDM) was simulated. The breakdown, oscillation and vanishing stage of the discharge channel were analyzed, and the crater after machining was obtained. Finally, a single-pulse discharge experiment during EDM was conducted to verify the simulation model.FindingsDuring the breakdown of the discharge channel, the electrons move towards the center of the discharge channel. The electrons at the end diverge due to the action of water resistance, making the discharge channel appear wide at both ends and narrow in the middle, showing the pinch effect. Due to the mutual attraction of electrons and positive ions in the channel, the transverse oscillation of the discharge channel is shown on the micro level. Therefore, the position of the discharge point on the workpiece changes. The longitudinal oscillation in the discharge channel causes the molten pool on the workpiece to be ejected due to the changing pressure. The experimental results show that the shape of the crater is similar to that in the simulation, which verifies the correctness of the simulation results and also proves that the crater generated by the single pulse discharge is essentially the result of the interaction between transverse wave and longitudinal wave.Originality/valueIn this paper, the simulation of the discharge breakdown process in EDM was carried out, and a new mathematical model that considers the MHD and the discharge channel oscillation was established. Based on the MHD module, the discharge breakdown, oscillation and vanishing stages were simulated, and the velocity field and pressure field in the discharge area were obtained.

Ultra-high speed video observations of intracloud lightning flash initiation

This study describes results from video observations of five intracloud flashes located ≤ 20 km from the camera and recorded with 6.1 µs exposure time and 6.66 µs frame intervals. Video data are supported with electric field change (E-change) and VHF measurements, with emphasis on the flash initiating event (IE) and initial breakdown (IB) stage. In four of the five flashes, the IE is accompanied by weak luminosity, ≤ 5% above background, lasting for 300–500 µs. Two of these four IEs were positive Narrow Bipolar Events (NBEs) with VHF powers of 43 and 990 W; these are the first (known) data showing visible light detected with a positive NBE. Two other IEs with weak luminosity had powers of 0.5 and 1 W, and the IE with no detected luminosity had a VHF power of 3 W. A typical IB cluster consists of several narrow pulses and one classic pulse in E-change data (along with many VHF pulses), and each example flash has 2–10 IB clusters in the first 5–50 ms. The luminosity of IB clusters was substantially greater than IE luminosity, ranging from 10 to 40% above background in four examples, while for one flash with 10 IB clusters, the luminosity range was 35–360% above background (average 190%). Luminosity durations of IB clusters were 520–1750 µs with average 1210 µs. For both IEs and IB clusters, increases in the detected luminosity were closely timed with substantial VHF emissions and decreased when VHF emissions weakened.