Accumulation Of Positive Charge Research Articles

Study of Discharge Inception and Propagation in Liquid–Solid Insulation System under DC–LI Superimposed Constraints

High-voltage direct current (HVDC) links are starting to become widely implemented thanks to their interesting advantages such as reduced operation losses, the absence of reactive power, which allows energy transport via underground cables over long distances, and improved power control. The latter advantage is very essential for renewable energy resource integration into power grids. However, a thorough understanding of the behavior of insulation systems for HVDC components is critical so as to ensure a more reliable service. Indeed, the existence of the direct current (DC) voltage in HVDC components may induce surface and space charge accumulation that can stress insulation further or even promote discharge inception and propagation. As such, this work focuses on showcasing the effect of surface charge on streamers that develop on the interface of liquid–solid insulation due to the advent of lightning impulse (LI) voltage in the HVDC link. This study was performed using finite-element-based numerical simulations that include a quasi-electrostatic model for surface charge accumulation and an electrohydrodynamic fluid model for streamer initiation and propagation. The geometry used was point–plane configuration where the high voltage is applied to the needle electrode located above the liquid–solid interface. The obtained results suggest that streamer initiation is affected by both the accumulated surface charge density and polarity. For a positive streamer, an accumulation of positive surface charge increases the discharge inception voltage as a result of a weakening in the electric field, while an accumulation of negative surface charge decreases the discharge inception voltage due to an intensification in the electric field. Moreover, streamer travel distance and velocity are also both shown to be affected by surface charge accumulation.

SOI-FET Sensors with Dielectrophoretic Concentration of Viruses and Proteins.

Quick label-free virus screening and highly sensitive analytical tools/techniques are becoming extremely important in a pandemic. In this study, we developed a biosensing device based on the silicon nanoribbon multichannel and dielectrophoretic controlled sensors functionalized with SARS-CoV-2 spike antibodies for the use as a platform for the detection and studding of properties of viruses and their protein components. Replicatively defective viral particles based on vesicular stomatitis viruses and HIV-1 were used as carrier molecules to deliver the target SARS-CoV-2 spike S-proteins to sensory elements. It was shown that fully CMOS-compatible nanoribbon sensors have the subattomolar sensitivity and dynamic range of 4 orders. Specific interaction between S-proteins and antibodies leads to the accumulation of the negative charge on the sensor surface. Nonspecific interactions of the viral particles lead to the positive charge accumulation. It was shown that dielectrophoretic controlled sensors allow to estimate the effective charge of the single virus at the sensor surface and separate it from the charge associated with the binding of target proteins with the sensor surface.

Total Ionizing Dose and Annealing Effects on Shift for p-GaN Gate AlGaN/GaN HEMTs

A research of total ionizing dose and annealing effects on Schottky type p-GaN gate Al0.2Ga0.8N/GaN high electron mobility transistors (HEMTs) has been carried out. Devices with breakdown voltages of 100V/200V/650V were irradiated under Co-60 X-rays. Radiation doses reach to a total amount of 500 krad (Si) with dose rate of 50 rad(Si)/s under gate biases of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{GS}=0\text{V}$ </tex-math></inline-formula> /+3V/+5V. Negative threshold voltage shifts were observed, especially under positive gate biases. It is found out that the threshold voltage shifts are due to the accumulation of positive charges (holes) trapped in the interface of p-GaN/AlGaN. Therefore, the shift amount is proportional to the gate bias and the radiation amount, while not related to the breakdown voltage. After the total ionizing dose experiments, both high temperature and room temperature annealing processes were taken. During the annealing processes, the shifted threshold voltage recovered, and high temperature accelerated the recovery process. Experiment results indicate that the total ionizing dose effect is recoverable.

Space charge characteristics of silicone elastomer for device packaging under positive square wave voltage

AbstractWith the rapid development of power electronic devices towards high voltage and power, the insulation challenges faced by devices have attracted widespread attention. Silicone elastomer is widely used in device packaging as one insulating material, and the study of its insulating properties is helpful to the reliable operation of devices. To this end we obtained the space charge characteristics of silicone elastomer under positive square wave voltage by using the pulse‐electroacoustic (PEA) method. Firstly based on the existing research and IEC standards, the selection criteria of the resistance and capacitance parameters of a PEA system for space charge measurement under square wave voltage are given. Through this experimental system, the space charge distribution under the positive square wave voltage with different waveform parameters is obtained, and the influences of the waveform parameters on the space charge accumulation are analysed. The amounts of charges under the action of square wave voltage with different waveform parameters are calculated, and the influences of waveform parameters on the amounts of charges are analysed. In addition, the reasons for the difference in the accumulation of positive and negative charges are explained through Schottky injection model, the synthesis reaction and the infrared spectrum of the silicone elastomer.

Ion-induced electron and hydrogen ions emission of lead-bismuth silicate glass by ToF

A micro-channel Plate (MCP) is a continuous photo-electron multiplier, which has been widely used in the field of particle detectors and low-light night vision imaging devices. The electrons produced by particles collision from the incident end of MCP constitute the useful signal, while the electrons and negative ions produced by collision of ions formed by ionizing gas molecules are considered noise. To reduce the noise from ion collisions, it is important to identify the electron and negative ion emissions caused by collision of unexpected ion. In this paper, the electron and hydrogen ion emissions caused by 1.5MeV Au2+ were analyzed for the cases of acid-etched, alkali-etched, and hydrogen reduced lead-bismuth silicate glass (LBSG). The Time of Flight (ToF) method was used to detect the electron and hydrogen ion emission yields of LBSG. Hydrogen reduction significantly increases the yield of ion-induced electron and negative ions, and the alkali treatment gets the higher yield compared to acid treatment. It is proved that the ToF method is feasible to detect the ion-induced negative particles emission and would be more effectively if the accumulation of positive charges is avoided. The results are valuable not only for noise analysis and manufacturing parameters optimization of low-noise and high-gain MCP, but also as a reference for preparation of new-type micro-channels and investigation on the electron emission properties of glass for space.

Investigation of Charge Accumulation and Decay Processes in Epoxy-Based Composites Using Quantum Chemical Calculations Under the Effect of Electric Field

This work investigates the influence of aluminum nitride (AlN) fillers on the charge dynamics of epoxy resin (EP) and its hybrid composites through space charge measurements and quantum chemical calculations (QCCs). QCCs analyze the energy-level orbitals and trap parameters of the molecules under the electric field. The pure EP exhibits a homo-charge accumulation, whereas fewer charges are accumulated in the EP hybrid composites. The AlN filler addition significantly suppresses the space charge accumulation during polarization and facilitates the charge dissipation during the depolarization due to the lower trap density than the pure EP. It is found that the orbital energy level of the combined reaction of all monomers together is not a simple superposition of individual orbital energy levels of different monomers. The increased charge injection barrier height suppresses space charge injection and accumulation. The electric field significantly influences the hole traps more than the electron traps. The positive charges with low mobility are easily trapped inside hole traps compared with the negative charges with high mobility inside the electron traps. This results in positive charge accumulation during the polarization and slow decay during the depolarization. The increase of the electrostatic potential is more uniform in hybrid composites than in the pure EP, and no visible electron migration is observed. It indicates that hybrid composites remain stable under electric fields. Moreover, it is not easy for the hole to transport due to the deep trap after the charge injection, leading to limited visible space charge accumulation near the anode.

The role of surface charge and its decay in surface dielectric barrier discharges

The charge accumulation and decay in surface dielectric barrier discharges (SDBDs) driven by a sine AC voltage waveform (4 kHz) in combination with a nanosecond positive voltage pulse (300 ns, 20 Hz) is experimentally investigated based on a combination of the electro-optical Pockels effect and a high-speed camera. It is found that the accumulation of positive surface charge on the dielectric promotes the discharge in the negative half cycle of the applied AC voltage, whereas it inhibits the development of following new positive charge filaments. The decay of a single positive charge filament on the surface is a result of the neutralization by negative charges that originate either from the migration of negative surface charge (electrons) or the drift of free electrons from the volume above the surface towards the surface. This work aims to contribute to a better understanding of the evolution of surface charge and its effects in SDBDs.

Characteristic studies on positive and negative streamers of double-sided pulsed surface dielectric barrier discharge

The mechanisms of streamer generation and propagation in double-sided pulsed surface dielectric barrier discharge (SDBD) on both sides have been analyzed and investigated by experiment and numerical simulation. The fully exposed asymmetric SDBD has two discharge processes located on the high voltage electrode (HVE) side and the ground electrode (GE) side. Discharge images of the HVE side and GE side are taken by a digital camera under continuous pulse and ICCD (Intensified Charge Coupled Device) is utilized to diagnose the generation and propagation of streamers in single pulse discharge. In order to understand the physical mechanisms of streamer evolution more deeply, we establish a 2D simulation model and analyze it from the aspects of electron density, ion density, reduced electric field and electron impact ionization source term. The results show that the primary and secondary discharges on the HVE side and the GE side of the double-sided SDBD are composed of positive streamer and negative streamer, respectively. On the HVE side, the accumulation of positive charges on the dielectric surface causes the direction of the electric field to reverse, which is the principal factor for the polarity reversal of the streamer. On the GE side, both the negative charges accumulated on the dielectric surface and the falling voltage are the key factors for the streamer polarity switch.

Electrical characterization of memory capacitors for nonvolatile memory applications based on nanolaminated HfO2/Al2O3 and Al-doped HfO2 stacks

Memory capacitors with atomic-layer-deposited HfO2/Al2O3 nanolaminated layers and Al-doped HfO2 charge trapping layers were investigated through capacitance-voltage (C-V) and current-voltage (I-V) measurements. The dielectric constant of the multi-dielectric stack comprising 20-nm Al2O3 blocking oxide, a HfO2-based layer and 2.4-nm tunnel SiO2 does not depend on the manner of Al-introduction in HfO2.The stacks exhibit a negative oxide charge of about -5.1×1011 cm−2 and -2.5×1011 cm−2 for the structures with nanolaminated and doped layers, respectively. The Al-doping of HfO2 is found to produce lower leakage currents. A sublinear behavior of the current-voltage curves is observed in the range of -20 ÷ +10 V for both HfO2-based stacks. Memory windows of ∼ 1 V when charging with ±27-V voltage pulses are obtained; the data suggests that electron trapping is better pronounced in the HfO2/Al2O3 nanolaminate, while positive charge accumulation prevails in the Al-doped HfO2 layers.

Effect of ionizing irradiation on charge distribution and breakdown of MOSFETs

The effect of ionizing radiation on the formation of charges at internal SiO2-Si (substrate) and external SiO2-Sips (gate) interfacial boundaries (IFB) and on the gate breakdown of MOSFETs is studied. It is shown that with an increase in the dose of ionizing radiation near the internal interfacial boundaries, a monotonous increase of positive charge in p-MOSFETs, and the accumulation of positive charges at first, and at doses above 105 rad the accumulation of negative charges in n-MOSFETs is observed. Near the external interfacial boundaries, at low radiation doses, positive charge accumulation is observed, and at doses &gt;106 rad, negative charge in both p- and n-MOSFETs is observed. Up to a dose of 108 rad ionizing radiation dies not have a noticeable effect on the gate breakdown voltage in both p- and n-MOSFETs at both bias polarities. The absence of influence is explained by a breakdown by mechanism of anode hole injection. Keywords: ionizing radiation, MOSFETs, charge accumulation, gate breakdown.

Surface modification of silicone rubber by CF4 radio frequency capacitively coupled plasma for improvement of flashover

The flashover performance of insulating materials plays an important role in the development of high-voltage insulation systems. In this paper, silicone rubber (SIR) is modified by CF4 radio frequency capacitively coupled plasma (CCP) for the improvement of surface insulation performance. The discharge mode and active particles of CCP are diagnosed by the digital single-lens reflex and the spectrometer. Scanning electron microscopy and x-ray photoelectron spectroscopy are used for the surface physicochemical properties of samples, while the surface charge dissipation, charge accumulation measurement, and flashover test are applied for the surface electrical characteristics. Experimental results show that the fluorocarbon groups can be grafted and the surface roughness increases after plasma treatment. Besides, the surface charge dissipation is decelerated and the positive charge accumulation is inhibited obviously for the treated samples. Furthermore, the surface flashover voltage can be increased by 26.67% after 10 min of treatment. It is considered that strong electron affinity of C–F and increased surface roughness can contribute to deepening surface traps, which not only inhibits the development of secondary electron emission avalanche but also alleviates the surface charge accumulation and finally improves the surface flashover voltage of SIR.

Light-activated interlayer contraction in two-dimensional perovskites for high-efficiency solar cells.

Understanding and tailoring the physical behaviour of halide perovskites under practical environments is critical for designing efficient and durable optoelectronic devices. Here, we report that continuous light illumination leads to >1% contraction in the out-of-plane direction in two-dimensional hybrid perovskites, which is reversible and strongly dependent on the specific superlattice packing. X-ray photoelectron spectroscopy measurements show that constant light illumination results in the accumulation of positive charges in the terminal iodine atoms, thereby enhancing the bonding character of inter-slab I-I interactions across the organic barrier and activating out-of-plane contraction. Correlated charge transport, structural and photovoltaic measurements confirm that the onset of the light-induced contraction is synchronized to a threefold increase in carrier mobility and conductivity, which is consistent with an increase in the electronic band dispersion predicted by first-principles calculations. Flux-dependent space-charge-limited current measurement reveals that light-induced interlayer contraction activates interlayer charge transport. The enhanced charge transport boosts the photovoltaic efficiency of two-dimensional perovskite solar cells up to 18.3% by increasing the device's fill factor and open-circuit voltage.

Surface strain and co-doping effect on Sm and Y co-doped BaCeO3 in proton conducting solid oxide fuel cells

Although promising, regulating the surface strain is still immature for enhance the performance of proton-conducting materials and no clear law has been found. In this work, surface strain and co-doping effect on dopant segregation, hydration reaction and proton transport of Sm and Y co-doped BaCeO3 (BCYS) in proton-conducting solid oxide fuel cells (P-SOFC) was investigated. We found that although the dopant segregation trend is reduced as the surface strain increase from −2% to 2%, which means that a large tensile strain is beneficial to enhance structural stability, oxygen vacancy formation energy and proton binding energy near the BCYS surface do not change monotonously with the surface strain. We found that the fewer electrons around the oxygen atoms before hydrogen adsorption, the more stable the proton. It is worth noting that 1% tensile strain is most favorable for enhancing the degree of surface hydration and proton transport in our calculation results, which helps to weaken the negative effects of the space charge layer formed by the accumulation of positive charges on the surface. The collocation of Sm and Y has a synergistic effect, which means Sm facilitates oxygen vacancy formation, while Y promotes hydration reaction. Moreover, the introduction of Sm and Y can hardly change the electronic conductivity of BCYS, which is conducive to the open circuit voltage of P-SOFC.

The characteristics of ion wind thruster based on dielectric barrier discharge in near space

The experimental results show that when the pressure is constant, with the increase of power, the thrust-power ratio of the thruster decreases, and the wind speed and thrust increase, but the increase rate gradually decreases and finally tends to be stable；When the pressure is 5.5 kPa, The rate of increase in thrust decreases the slowest, that is, the thruster has the maximum thrust potential at 5.5 kPa, and when the input power is greater than 75 W, the relative maximum thrust can be generated, reaching 14.8 μN; At the same time, with the increase of input power, the thrust - power ratio increases first and then decreases; When the input power is constant in the range of 15–65 W, as the air pressure increases, the wind speed decreases, and the thrust and thrust-power ratios all have local extremes, that is, when the air pressure is 8 kPa, it reaches the regional maximum, the maximum is 12.7 μN and 0.45 μN/W, respectively, at 16 kPa, it reaches the minimum value of the area, and the minimum is 4 μN and 0.14 μN/W, respectively. By comparing the discharge images under different atmospheric pressures, it can be concluded that the thrust generated by the accelerated collision of particles with a single short-time large current pulse is less than that generated by the accelerated collision of ions with a long-time small high-frequency pulse discharge, and the particle collision probability is the main reason affecting the wind speed; Meanwhile, with the increase of input power, the “virtual electrode” formed by the accumulation of positive ion space charge reduces the increase rate of wind speed and thrust.

Experimental investigation on cathode layer of surface dielectric barrier discharge plasma by surface potential measurement

The cathode layer of surface dielectric barrier discharge plasma is investigated experimentally by using the surface potential measurement under different bias voltages. Positive charge accumulation is found near the edge of the exposed electrode (x = 0 mm) under negative DC bias voltage. In addition, the plasma electromotive force (EMF) distribution curve near the edge of the exposed electrode diverges with the negative DC bias voltage. These phenomena are in good agreement with the conclusion that the cathode layer shows positive potential in time average. Five actuators with different exposed electrode widths are designed to study the relationship between the cathode layer and the mechanical properties of the actuator. With the widening of the exposed electrode, the positive charges in the cathode layer increase, and the plasma EMF divergence is more pronounced. However, the thrust force decreases. Moreover, the variation of thrust force with DC bias voltage is consistent with the change of the plasma EMF. The experimental results show that the narrow-exposed electrode actuator for the cathode layer with a small size and low number of positive ions has better mechanical properties. By analysis, this is mainly due to the lower number of positive ions of the cathode layer, producing less shielding from the applied voltage. More electrons are emitted from the cathode layer. This paper provides a method for the detection and study of the cathode layer. In addition, it can provide insight into how the cathode layer affects the development of thrust force.

On the Transition From Precursors to the Initial Upward Positive Leader in Negative Rocket‐Triggered Lightning

AbstractPrecursory current pulses (precursors) and initial upward leader pulses are examined to characterize the charge transfer of precursors and the sustained upward leader during the early stage of rocket‐triggered lightning. According to the analysis of six negative triggered flashes, it is found that both precursors and the initial upward positive leader (iUPL) pulse are led by a small deflection that appears at about 25 μs prior to the major pulses. The characteristics of precursors and iUPL pulses are very similar except that the precursors generally transfer less electric charge (35.07 μC on average) than iUPL pulses do (64.73 μC on average). Some marginal differences in the parameters (e.g., rise time, duration) may be attributed to the modification of the current pulses caused by the different impedances of the leader channel and the steel wire. The ascending rocket causes the enhancement of electric field (E‐field) in the close vicinity of the wire tip, and therefore the breakdown of the iUPL is initiated by a stronger E‐field than that of the precursors. The step lengths of the precursors (defined as the extended length of the wire tip lifted by the rocket between two adjacent isolated precursors) are similar to that of iUPL pulses. Our analyses indicate that the transition from precursors to the iUPL occurs when the E‐field around the wire tip is strong enough, by the accumulation of more positive charge, to launch a meter‐scale breakdown and the ensuing charge transfer to ground.

K Deprivation Modulates the Primary Metabolites and Increases Putrescine Concentration in Brassica napus.

Potassium (K) plays a crucial role in plant growth and development and is involved in different physiological and biochemical functions in plants. Brassica napus needs higher amount of nutrients like nitrogen (N), K, phosphorus (P), sulfur (S), and boron (B) than cereal crops. Previous studies in B. napus are mainly focused on the role of N and S or combined deficiencies. Hence, little is known about the response of B. napus to K deficiency. Here, a physiological, biochemical, and molecular analysis led us to investigate the response of hydroponically grown B. napus plants to K deficiency. The results showed that B. napus was highly sensitive to the lack of K. The lower uptake and translocation of K induced BnaHAK5 expression and significantly declined the growth of B. napus after 14 days of K starvation. The lower availability of K was associated with a decrease in the concentration of both S and N and modulated the genes involved in their uptake and transport. In addition, the lack of K induced an increase in Ca2+ and Mg2+ concentration which led partially to the accumulation of positive charge. Moreover, a decrease in the level of arginine as a positively charged amino acid was observed which was correlated with a substantial increase in the polyamine, putrescine (Put). Furthermore, K deficiency induced the expression of BnaNCED3 as a key gene in abscisic acid (ABA) biosynthetic pathway which was associated with an increase in the levels of ABA. Our findings provided a better understanding of the response of B. napus to K starvation and will be useful for considering the importance of K nutrition in this crop.

Molecular engineering towards efficientwhite-light-emitting perovskite

Low-dimensional hybrid perovskites have demonstrated excellent performance as white-light emitters. The broadband white emission originates from self-trapped excitons (STEs). Since the mechanism of STEs formation in perovskites is still not clear, preparing new low-dimensional white perovskites relies mostly on screening lots of intercalated organic molecules rather than rational design. Here, we report an atom-substituting strategy to trigger STEs formation in layered perovskites. Halogen-substituted phenyl molecules are applied to synthesize perovskite crystals. The halogen-substituents will withdraw electrons from the branched chain (-R-NH3+) of the phenyl molecule. This will result in positive charge accumulation on -R-NH3+, and thus stronger Coulomb force of bond (-R-NH3+)-(PbBr42−), which facilitates excitons self-trapping. Our designed white perovskites exhibit photoluminescence quantum yield of 32%, color-rendering index of near 90 and chromaticity coordinates close to standard white-light. Our joint experiment-theory study provides insights into the STEs formation in perovskites and will benefit tailoring white perovskites with boosting performance.

Discriminating the Multi-Frequency Microwave Brightness Temperature Anomalies Relating to 2017 Mw 7.3 Sarpol Zahab (Iran-Iraq Border) Earthquake

A Mw 7.3 earthquake occurred near the Iran-Iraq border on November 12, 2017, as the result of oblique-thrust squeezing of the Eurasian plate and the Arabian plate. By employing the spatio-temporally weighted two-step method (STW-TSM) and microwave brightness temperature (MBT) data from AMSR-2 instrument on board Aqua satellite, this paper investigates carefully the spatiotemporal features of multi-frequency MBT anomalies relating to the earthquake. Soil moisture (SM), satellite cloud image, regional geological map and surface landcover data are utilized to discriminate the potential MBT anomalies revealed from STW-TSM. The low-frequency MBT residual images shows that positive anomalies mainly occurred in the mountainous Urmia lake and the plain region, which were 300 km north and 200 km southwest about to the epicenter, respectively. The north MBT anomaly firstly appeared 51 days before the mainshock and its magnitude increased over time with a maximum of about +40K. Then the anomaly disappeared 3 days before, reappeared 1d after and diminished completely 10 days after the mainshock. Meanwhile, the southwest MBT anomaly firstly occurred 18 days before and peaked 3 days before the mainshock with a maximum of about +20K, and then diminished gradually with aftershocks. It is speculated that the positive MBT anomaly in the Urmia lake was caused by microwave dielectric property change of water body due to gas bubbles leaking from the bottom of the lake disturbed by local crust stress alteration, while the southwest MBT positive anomaly was caused by microwave dielectric constant change of shallow surface due to accumulation of seismically-activated positive charges originated at deep crust. Besides, some accidental abnormal residual stripes existed in line with satellite orbit, which turned out to be periodic data errors of the satellite sensor. High-frequency MBT residual images exhibit some significant negative anomalies, including a narrow stripe pointing to the forthcoming epicenter, which were confirmed to be caused by synchronous altostratus clouds. This study is of guidance meaning for distinguishing non-seismic disturbances and identifying seismic MBT anomaly before, during and after some large earthquakes.

Enhanced sensitivity of graphene nanoribbon gas sensor for detection of oxides of nitrogen using boron and phosphorus co-doped system: A first principles study

The adsorption of toxic gases Nitrogen Oxide (NO) and Nitrogen Dioxide (NO2) on armchair graphene nanoribbon substrate and its co-doped system has been investigated. Density Functional Theory (DFT) is used to explain the gas sensing performance of Boron (B) doped and Boron-Phosphorus (BP) co-doped armchair graphene nanoribbon (BCmPn-Gr; m,n = 0,1,2,3 and m + n = 3) for detection of these gases. The change in electronic and structural characteristics of armchair graphene nanoribbon (ArGNRs) before and after sensing of NO and NO2 gases is reported. Different configurations are used in our work such as Pristine, Boron doped and Boron-Phosphorus co-doped ArGNRs. Boron site is observed to be active site to study adsorption phenomenon due to accumulation of positive charge around it. Boron-Phosphorus based formation shows considerable enhancement of adsorption capabilities as compared to pristine structure alone. A significant increase in adsorption of NO and NO2 gases with increase in amount of Phosphorus atoms is observed. This work reveals that Boron Phosphorus co-doped system is considerably better than previously reported similar works. It can be utilized as effective gas sensing material.