Charge Deposition Research Articles

Method for noncontact measurement of 2DEG mobility and carrier density in AlGaN/GaN on semi-insulating wafers

We present a charge-assisted sheet resistance technique for noncontact wafer level determination of two-dimensional electron gas (2DEG) mobility versus sheet carrier density without any test structures or gates. Instead, the electrical biasing of the 2DEG is provided by surface charge deposition, using a corona charging method. Analysis of the sheet resistance versus deposited charge identifies the 2DEG full depletion condition and enables calculation of the 2DEG sheet carrier density required for the mobility. Results for AlGaN/GaN heterostructures on semi-insulating SiC and sapphire substrates show good agreement with Hall results at a zero-bias condition.

On the slow ionization waves forming the breakdown in a long capillary tube with helium at low pressure

The results of studies of an electrical breakdown leading to the glow discharge ignition in a long capillary quartz tube are presented. Under such conditions, the breakdown completion is preceded by the development of direct, backward, and counter slow ionization waves (IWs) traveling in the tube. The initiation of the waves was created in helium at low pressure (P = 10 Torr) by the high-voltage pulses of positive and negative polarity with amplitude of several kilovolts. In the beginning, the regime without the breakdown completion in the tube was studied. In this regime, the propagation of only direct positive and direct negative IWs happens. The research on dynamics of the direct, backward, and counter positive and negative waves followed by a complete breakdown was done as well. The influence of the pre-existing plasma on the IWs propagation was also studied. The plasma was created in advance by low-current glow discharge being formed in the tube. The instant images of IWs were correlated with the electrical currents formed by the waves, that is, with the displacement current through the dielectric wall and the conductive current through the plasma column. In the experiments, the fine-sectioned electrode wrapped around the lateral tube surface was used. The usage of such electrode allowed one to study the dynamics of the surface charge deposition and deletion happening during the direct and backward wave propagation, respectively. Finally, a strong difference in the spatial structure and velocity of positive and negative direct waves traveling through non-ionized gas was revealed. Contrary, both the positive and negative backward waves traveling through the plasma formed by previous direct waves have the parameters close to each other.

Axion string signatures: a cosmological plasma collider

We study early and late time signatures of both QCD axion strings and hyperlight axion strings (axiverse strings). We focus on charge deposition onto axion strings from electromagnetic fields and subsequent novel neutralizing mechanisms due to bound state formation. While early universe signatures appear unlikely, there are a plethora of late time signatures. Axion strings passing through galaxies obtain a huge charge density, which is neutralized by a dense plasma of bound state Standard Model particles forming a one dimensional “atom”. The charged wave packets on the string, as well as the dense plasma outside, travel at nearly the speed of light along the string. These packets of high energy plasma collide with a center of mass energy of up to 109 GeV. These collisions can have luminosities up to seven orders of magnitude larger than the solar luminosity, and last for thousands of years, making them visible at radio telescopes even when they occur cosmologically far away. The new observables are complementary to the CMB observables for hyperlight axion strings that have been recently proposed, and are sensitive to a similar motivated parameter range.

GEANT4 simulation study of the response of a miniature radiation detector in Galactic Cosmic Rays and inside a spacecraft

The Miniaturized Detector for Application in Space (MIDAS) is a compact device with dimensions 5 × 5 × 1 cm3that combines position-sensitive Si detectors and a fast neutrons spectrometer. MIDAS is developed with the purpose of acting as a linear energy transfer (LET) spectrometer for the charged particles and measuring dose and dose equivalent from both charged particles and neutrons. It is based on fully depleted monolithic active Si pixel sensors for the charged track and energy deposition measurements, while a plastic scintillator read out by a silicon photomultiplier is used to determine energy depositions from fast neutrons. A simulation study of the detector response in galactic cosmic ray (GCR) radiation fields with the aid of GEANT4 has been performed. Energy depositions and hit pixel addresses have been used to reconstruct tracks and calculate LET spectra. A method to calculate LET∞in water from the measured LET has been elaborated. The dose rate in water and dose equivalent rate has been calculated. The energy and particle composition of the radiation field produced by the interaction of GCR with the Al walls of a spacecraft model has been determined, and the response of MIDAS in this radiation field has been investigated.

Stable transmission of low energy electrons in glass tube with outer surface grounded conductively shielding

<sec>The electron microbeam is useful for modifying certain fragments of biomolecule. It is successful to apply the guiding effect to making the microbeam of positively charged particles by using single glass capillary. However, the mechanism for the electron transport through insulating capillaries is unclear. Meanwhile, previous researches show that there are oscillations of the transmission intensity of electrons with time in the glass capillaries with outer serface having no grounded conductive shielding, So, the application of glass capillary to making the microbeam of electrons is limited.</sec><sec>In this paper, the transmission of 1.5 and 0.9 keV electrons through the glass capillary without/with the grounded conductive-coated outer surface are investigated, respectively. This study aims to understand the mechanism for low energy electron transport in the glass capillaries, and find the conditions for the steady transport of the electrons. Two-dimensional angular distribution of the transported electrons and its time evolution are measured. It is found that the intensity of the transported electrons with the incident energy through the glass capillaries for the glass capillaries without and with the grounded conductive-coated outer surface show the typical geometrical transmission characteristics. The time evolution of the 1.5- keV electron transport presents an extremely complex variation for the glass capillary without the grounded conductive-coated outer surface. The intensity first falls, then rises and finally oscillates around a certain mean value. Correspondingly, the angular distribution center experiences moving towards positive-negative-settlement. In comparison, the charge-up process of the 0.9 keV electron transport through the glass capillary with the grounded conductive-coated outer surface shows a relatively simple behavior. At first, the intensity declines rapidly with time. Then, it slowly rises till a certain value and stays steady subsequently. The angular distribution of transported electrons follows the intensity distribution in general, but with some delay. It quickly moves to negative direction then comes back to positive direction. Finally, it regresses extremely slowly and ends up around the tilt angle. To better understand the physics behind the observed phenomena, the simulation for the interaction of the electrons with SiO<sub>2</sub> material is performed to obtain the possible deposited charge distribution by the CASINO code. Based on the analysis of the experimental results and the simulated charge deposition, the conditions for stabilizing the electron transport through glass capillary arepresented.</sec>

Application of Corona Charge Deposition Technique in Thin Film Industry

With the advent of new materials, microchip industry is investigating new architecture to further scale down the device size. New technologies are on the way to achieving this goal without compromising with the device’s performance and benefits. In this new scenario, corona charge deposition technique (CCDT) has become an indispensable part of the thin film industry. Due to the non-invasive and non-destructive nature of corona charge ions, they are effectively being used to improve the device properties. They are also useful to understand the electrical properties of insulators and other materials. Corona-Kelvin non-contact metrology or the C-KM is the most recent development in this field. In this review, the applications of corona charge deposition technique in the semiconductor industry have been reviewed. Further, the methodology involved is described. The advances as well as challenges and improvements including the future research are also discussed.

Roll-to-roll manufacturing toward lab-to-fab-translation of perovskite solar cells

Perovskite solar cells (PSCs) are emerging next-generation photovoltaics, and some breakthroughs for the commercialization have been rapidly made. To develop the technologies for large-area modules, economically feasible fabrication using a roll-to-roll (R2R) solution process may be the ultimate target for the fabrication of PSCs. In order to achieve successful R2R production of PSCs, however, several issues still need to be addressed. Roll-based continuous and scalable deposition of perovskite and charge transporting layers on a flexible substrate needs to be developed to obtain high-quality R2R-processed PSCs. There are also critical factors involved in accomplishing R2R fabrication: heat treatment at low temperature and a short processing time over the whole process with industrial-compatible methods. We briefly discuss this perspective: scalable deposition of layers, considerations for the R2R process, and progress and challenges in the R2R fabrication of the PSCs.

Features of a negative ionization wave development preceding the full breakdown in a long capillary tube wrapped with a continuous or fine-sectioned grounded electrode

The experimental results on the study of negative ionization wave propagating along a long capillary tube are presented. The ionization wave was initiated by high-voltage pulse of negative polarity. The propagation of this surface ionization wave precedes and influences the establishment of complete electric breakdown within the tube. The spreading of this wave is accompanied by the surface charge deposition. The usage of the fine-sectioned outer electrode allows one to find out the general features of a negative ionization wave. The main of them is the tight correlation between local currents determining the formation of local surface charge and visual discharge images taken by the fast camera characterizing the pace of the ionization wave propagation.

Radial current distribution along the ionization wave propagating in a long dielectric capillary tube filled with a low-pressure helium

The experimental results on the study of the ionization wave propagating along a long capillary tube are presented. The ionization wave was initiated by high-voltage pulse of positive or negative polarity. The propagation of this surface ionization wave precedes and influences the establishment of complete electric breakdown within the tube. The spreading of this wave is accompanied by the surface charge deposition. The usage of the fine-sectioned outer electrode allows one to find out the general features of the ionization waves.

Ionization wave propagation in a long capillary tube in the presence of a low-current glow discharge in low-pressure helium

The experimental results on the study of the positive ionization wave propagating along a long capillary tube are presented. The ionization wave was initiated by eigther high-voltage pulse of positive polarity applied over a long capillary tube with helium or high-voltage pulse applied over the same tube but in presence of low-current glow discharge. The spreading of this wave is accompanied by the surface charge deposition. The usage of the fine-sectioned outer electrode allows one to find out the features of the positive ionization wave in both cases (with or without low-current discharge).

Plasma-assisted dry reforming of methane over Mo2C-Ni/Al2O3 catalysts: Effects of β-Mo2C promoter

Non-thermal plasma (NTP) coupled with catalysis provides a way to enable the dry reforming of methane (DRM) reaction to occur at low temperatures. While assistance of NTP brings the negative issue of coke deposition due to the faster rate of CH4 dissociation induced by NTP. Herein, β-Mo2C was employed as an effective component to activate CO2 and collaborated with Ni/γ-Al2O3 for the plasma-assisted DRM reaction. Addition of β-Mo2C facilitated the charge deposition, and Ni nanoparticles were found to re-disperse over the β-Mo2C surface due to the strong interaction between Ni and β-Mo2C. Benefiting from the new active interface of Ni-Mo2C, the mechanically mixed Mo2C-Ni/Al2O3 catalyst exhibited much better activity and stability as compared with the undoped Ni/Al2O3 catalyst. The present study reveals the crucial roles of β-Mo2C additives, providing practical solutions to depress carbon deposition, and thereby enhance the catalytic stability in plasma-assisted DRM reaction.

Numerical simulation of surface charge inhibition performance on epoxy insulator under DC voltage by flexible coating strategy

Epoxy insulator is affected by surface charge accumulation under a strong electric field, which causes a decrease in the surface flashover voltage, threatening the safe operation of power equipment. This study reports on a flexible coating strategy for the insulator to inhibit the charge accumulation through numerical simulation. The experiment was conducted initially to reveal the charge accumulation feature. Then, the flexible coating method was proposed, in which the insulator surface was divided into three parts, and surface coatings with various conductivities were painted on the designated areas to adjust the charge distribution. Finally, the efficiency of such a coating strategy was estimated considering the temperature gradient. The results presented that the homo-charge was mostly deposited on the non-planar area of the spacer. The maximum charge density first decreased and then increased with increasing surface conductivity. The charge accumulation could be restrained by increasing the surface conductivity of insulator effectively. A significant suppression was achieved by properly coating with high conductivity at the non-planar region and with low conductivity at the planar region. The suppression performance of such a strategy became reduced as the temperature gradient increased. The results indicate that the flexible coating can balance charge deposition in the non-planar region and restrain charge injection near the electrode, thereby inhibiting the charge accumulation.

Plasma synthesis of ammonia in a tangled wire dielectric barrier discharge reactor: Effect of electrode materials

Plasma synthesis of NH3 from N2 and renewable H2 under mild conditions is very attractive for decentralised sustainable green ammonia production using intermittent renewables. In this study, NH3 synthesis was performed under ambient conditions in a dielectric barrier discharge (DBD) plasma reactor. Different tangled wire internal electrodes were employed to understand the influence of electrode materials on plasma ammonia synthesis. Compared with a rod electrode, a tangled wire electrode substantially enhanced the NH3 concentration and reduced the energy cost for ammonia production, which can be attributed to the expanded surface area and the chemisorption properties of the tangled electrodes. The influence of the N2/H2 molar ratio and total flow rate on the reaction performance was also evaluated. The lowest energy cost (59.0 MJ mol−1) for ammonia production was achieved using a Cu tangled electrode at a total flow rate of 250 ml min−1 and a discharge power of 20 W. The electrical diagnostics of the plasma process showed that the tangled wire electrodes decreased the breakdown voltage of the DBD and enhanced charge deposition, which enhanced the NH3 production. The reaction mechanism was discussed for the process optimisation of ammonia synthesis in a tangled wire DBD system.

Virtual walls for dielectric fluid manipulation through controllable charge deposition

Fluid transportation is a basic physical process in various engineering applications, and solid walls are most commonly used to confine fluid flows. Solid walls, however, have some disadvantages, including large pressure drops and plaguing by fouling. Here we experimentally demonstrate a method of controlling dielectric fluid flows on planar surfaces by virtual (not solid) walls through a spatially controlled charge deposition. Acting on the three-phase contact line, an electrically induced pressure has the same function as solid sidewalls. Dielectric fluids can be confined within designated areas, or flow directionally with the aid of contactless masks. Dielectric fluids can also move on planar surfaces by moving contactless masks. Due to the virtual wall effect of this novel method, an open channel can be developed to continuously transport fluids. The method may provide a new perspective to manipulating dielectric liquid flows and can be an alternative way of open fluidic devices.

Simulation study of the response of a highly sensitive silver-activation detector for neutron detection using MCNP code

In this paper, simulations were carried out using Monte-Carlo N-Particle MCNP-4C code to determine the energy dependence of the response of a highly sensitive silver-activation detector used for fast-neutron detection after moderated to thermal neutrons. The detector consists of sandwiched alternating thin-sheets of silver and crystal scintillator Anthracene. The simulations also had considered different materials and designs to get the most efficient design for detecting signals from fast-neutrons interactions with the active materials (silver) and the scintillator. The energy and charge depositions of photons and electrons created by fast-neutron interactions with detector within the detection-cell were simulated for different scenarios. Owing on the simulations, a method to maximize the response by modifying the design was identified. The optimal configurations are suitable for a wide range of monitoring and detecting neutron sources especially for big detectors implemented for security purposes, where the costs and weighs can be reduced significantly.

The Timing Resolution of IHEP-NDL LGAD Sensors With Different Active Layer Thicknesses

The thickness of the high-resistivity layer (activelayer) is a crucial factor affecting the timing resolution oflow gain avalanche diodes (LGADs). We studied the poten-tial improvement of the timing resolution of charge particlesbased on LGADs with different active layer thicknesses. TheInstitute of High Energy Physics (IHEP) and the Novel DeviceLaboratory (NDL) jointly designed two types of LGAD sensorswith active layer thicknesses of 33 and 50μm. The timingresolution is given by contributions from the time walk, jitter,and nonuniform charge deposition (Landau term). The jitterand the Landau term contributions in the timing resolution areextracted by the combination of the90Srbeta source test andthe picosecond laser test. The Landau contribution is found tobe the dominant contribution for both types of LGAD sensors,and the Landau contribution of the 33μm sensor is lowerthan that of the 50μm sensor. Based on the experimentalresults, we perform the simulation for thinner active layer LGADwith the WeightField2 program. The timing resolution can befurther improved by reducing the active layer thickness from33 to 20μm.

A non-equal gap distance dielectric barrier discharge: between a wedge-shaped and a plane-shaped electrode

For all volume dielectric barrier discharges (DBDs) reported, including both planar configuration volume DBDs and cylindrical or coaxial volume DBDs, the gap distance between the two electrodes is always a constant. In this paper, a non-equal gap distance DBD between a wedge electrode and a plane-shaped electrode is reported. It is found that the plasma can self-organize into a striped shape, which makes it possible to achieve a homogeneous plasma treatment effect by scanning the plasma over the surface. The high-speed photographs show that the discharge first occurs at the center of the wedge-shaped electrode where the gap distance is smallest, and it jumps to the next position with a relatively larger gap distance after a certain delay time. This is because of the build up of the reverse voltage due to the deposit of charges at the locations where discharge is ignited. Detailed analysis shows that the width of the equivalent charge deposit region is larger than that of the bright plasma stripe. According to the intensity ratio of N2 + (391.4 nm) and N2 (394.3 nm), the reduced electric field strength is evaluated to be in the range of 250–370 Td. It decreases with the increase in the gap distance. In addition, plasma of another type of non-equal gap distance DBD with a conical shape and a plane-shaped electrode is explored, and it is found that the plasma can also self-organize into concentric rings.

Simulation of positive streamer propagation in an air gap with a GFRP composite barrier

The puncture of glass fibre reinforced polymer (GFRP) laminate is a primary damage pattern of wind turbine blades due to lightning strikes. A numerical simulation model of positive streamer propagation in a needle-to-plate air gap with a GFRP laminate is established to investigate the breakdown mechanism of GFRP laminate. The model not only considers the dynamics of charged particles in the air and the composite laminate, but also the current continuity at gas–solid interfaces. The simulated streamer discharge pattern and the surface streamer length are in good agreement with the observation results. The distributions and evolutions of the electron number density, electric field, and surface charge densities during streamer propagation are obtained. It is found that the enhancement of the electric field on the GFRP laminate is caused by the rapid deposition of positive and negative space charges on the GFRP laminate after a secondary streamer incepts on the lower surface of the GFRP laminate. The effects of the applied voltage, relative permittivity, and thickness of the GFRP laminate on the electric field on the GFRP laminate are investigated. The obtained results could assist in further understanding of the mechanism of GFRP wind blade breakdown due to lightning strikes.

Sensitivity of heavy-ion-induced single event burnout in SiC MOSFET

The energy deposition and electrothermal behavior of SiC metal–oxide–semiconductor field-effect transistor (MOSFET) under heavy ion radiation are investigated based on Monte Carlo method and TCAD numerical simulation. The Monte Carlo simulation results show that the density of heavy ion-induced energy deposition is the largest in the center of the heavy ion track. The time for energy deposition in SiC is on the order of picoseconds. The TCAD is used to simulate the single event burnout (SEB) sensitivity of SiC MOSFET at four representative incident positions and four incident depths. When heavy ions strike vertically from SiC MOSFET source electrode, the SiC MOSFET has the shortest SEB time and the lowest SEB voltage with respect to direct strike from the epitaxial layer, strike from the channel, and strike from the body diode region. High current and strong electric field simultaneously appear in the local area of SiC MOSFET, resulting in excessive power dissipation, further leading to excessive high lattice temperature. The gate–source junction area and the substrate–epitaxial layer junction area are both the regions where the SiC lattice temperature first reaches the SEB critical temperature. In the SEB simulation of SiC MOSFET at different incident depths, when the incident depth does not exceed the device’s epitaxial layer, the heavy-ion-induced charge deposition is not enough to make lattice temperature reach the SEB critical temperature.

Noise and error analysis and optimization in particle-based kinetic plasma simulations

In this paper we analyze the noise in macro-particle methods used in plasma physics and fluid dynamics, leading to approaches for minimizing the total error, focusing on electrostatic models in one dimension. We begin by describing kernel density estimation for continuous values of the spatial variable x, expressing the kernel in a form in which its shape and width are represented separately. The covariance matrix C(x,y) of the noise in the density is computed, first for uniform true density. The bandwidth of the covariance matrix is related to the width of the kernel. A feature that stands out is the presence of constant negative terms in the elements of the covariance matrix both on and off-diagonal. These negative correlations are related to the fact that the total number of particles is fixed at each time step; they also lead to the property ∫C(x,y)dy=0. We investigate the effect of these negative correlations on the electric field computed by Gauss's law, finding that the noise in the electric field is related to a process called the Ornstein-Uhlenbeck bridge, leading to a covariance matrix of the electric field with variance significantly reduced relative to that of a Brownian process.For non-constant density, ρ(x), still with continuous x, we analyze the total error in the density estimation and discuss it in terms of bias-variance optimization (BVO). For some characteristic length l, determined by the density and its second derivative, and kernel width h, having too few particles within h leads to too much variance; for h that is large relative to l, there is too much smoothing of the density. The optimum between these two limits is found by BVO. For kernels of the same width, it is shown that this optimum (minimum) is weakly sensitive to the kernel shape.We repeat the analysis for x discretized on a grid. In this case the charge deposition rule is determined by a particle shape. An important property to be respected in the discrete system is the exact preservation of total charge on the grid; this property is necessary to ensure that the electric field is equal at both ends, consistent with periodic boundary conditions. We find that if the particle shapes satisfy a partition of unity property, the particle charge deposited on the grid is conserved exactly. Further, if the particle shape is expressed as the convolution of a kernel with another kernel that satisfies the partition of unity, then the particle shape obeys the partition of unity. This property holds for kernels of arbitrary width, including widths that are not integer multiples of the grid spacing.We show results relaxing the approximations used to do BVO optimization analytically, by doing numerical computations of the total error as a function of the kernel width, on a grid in x. The comparison between numerical and analytical results shows good agreement over a range of particle shapes.We discuss the practical implications of our results, including the criteria for design and implementation of computationally efficient particle shapes that take advantage of the developed theory.