Charge Deposition Research Articles

Corrections on radial edge errors of charge and current density deposition for two-dimension radial-axial particle-in-cell simulations

Corrections on radial edge errors of charge and current density deposition for two-dimension radial-axial particle-in-cell simulations

Charged Microdroplets Deposition for Nanostructured-Based Electrode Surface Modification

Accelerated synthesis of gold nanoparticles (AuNPs) in charged microdroplets produced by electrospray ionization (ESI) was exploited to modify the surface of graphite screen-printed electrodes (GSPEs). The deposited AuNPs were then functionalized by the charged microdroplets deposition of 6-ferrocenyl-hexanethiol (6Fc-ht) solutions that act as reducing and stabilizing agents and provide electrochemical properties for the modified electrodes. The morphology and composition of the AuNPs were characterized by scanning electron microscopy (SEM). Cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behavior of the modified electrodes. The results showed that the ESI microdroplets deposition technique produces uniform and well-dispersed AuNPs on GSPE, and optimal conditions for deposition were identified, enhancing GSPE electrocatalytic performance. Further functionalization by ESI microdroplets of AuNPs with 6Fc-ht demonstrated improved redox properties compared with the conventional self-assembled monolayer (SAM) method, highlighting the technique’s potential for the easy and fast functionalization of electrochemical sensors.

Direct observation of particle clustering and gas breakdown in charged granular streams

The dust layer formed by charged particles deposition significantly limit the collection efficiency and stable application of electrostatic precipitators (ESPs). However, the deposition characteristics and re-entrainment mechanism of charged particles in electric field still remain unclear. In this study, a transparent ESP was designed to investigate the dynamic process of charged particle deposition, clustering and gas breakdown in electric field. The results showed that deposited particles will aggregate and gradually grow in chains in high-voltage electric field. The length of chain agglomerates can exceed 10 mm. And interelectrode gas breakdown could suddenly occur, which significantly changed the particle charging characteristics and increased particle emission at the outlet. In addition, a perforated plate was proposed to inhibit the gas breakdown and particle re-entrainment. The mass concentrations of particle re-entrainment decreased by 85.2 % and 79.1 % for the spike electrode and the arista electrode at the applied voltage of 30 kV, respectively.

Charge monitoring of test masses in gravitational waves interferometers

The sensitivity of gravitational waves (GWs) detectors is impacted by several sources of noise. One such source is related to the deposition of charge on the test masses (TMs), since its interaction with the surrounding electrical fields introduces an unwanted non-gravitational force on the TM. The charging process is still not completely understood and the charge deposition has historically never been consistently monitored, therefore we propose to implement a real-time monitoring system to overcome these limitations. In particular, in our work we explored 32 candidate sensor locations. Using simulation, we considered more than 100,000 different Gaussian-distributed charge located on either the front or back face of the TM. Utilizing dimensional reduction theories, like the PCA, we established sensor selection criteria to individuate the most relevant sensors. Exploiting Neural Networks (NNs), trained on the simulations, we determined the charge distributions.

Turbulence Embedded Into the Ionosphere by Electromagnetic Waves

AbstractWhen charged particles are accelerated from Earth's magnetosphere and precipitate into the atmosphere, their impact with neutral gas creates the aurora. Structured electric fields drive the acceleration processes but they are also passed down to the ionosphere, meaning that turbulence can in part be embedded into the ionosphere rather than emerge through instability processes locally. Applying a point‐cloud analysis technique adapted from observational cosmology, we show how observed turbulence in the ionosphere matches electrical current signatures in the pulsating aurora in a series of conjunctions between space‐ and ground‐based instruments. We propose that the temporal spectrum of pulsations in the pulsating aurora is the driver of a clearly observed energy injection into the ionosphere's unstable bottomside. Precipitating electrons produce electric fields through charge deposition, and we observe wave characteristics that are present in this pattern. Next, the relative electron‐ion drifts excite the Farley‐Buneman instability, the distribution of whose waves are organized according to the local electric field. It is the temporal characteristics of chorus wave interactions in the magnetosphere that is imparted, via precipitating electrons, to the pulsating aurora, and so we propose that chorus wave interactions are capable of embedding turbulent structure into the ionosphere. This structure (now pressure gradients) dissipate energy in the E‐region through turbulent processes, observed by the icebear coherent scatter radar.

Characterization of diamond and organic scintillation detectors utilizing radiation sources for continuous plasma operation.

This paper provides a comprehensive study of neutron calibration methodologies, specifically highlighting the capabilities for n-γ discrimination in diamond and EJ-309, and stilbene scintillation detectors. The calibration process detailed in this study includes pulse height analysis and pulse shape discrimination, relying on the analysis of charge deposition resulting from both γ and neutron interactions. Utilizing 60Co and 252Cf radiation sources, the energy spectra of these sources are obtained. The characterized detectors were used in ST40 experiments and allowed acquiring neutron signal during a plasma shot with good agreement among diamond and scintillation detectors. Then, the diamond detector was cross-calibrated against indium activation foils placed at the same location in proximity to the ST40 during plasma shots: both detectors measured a neutron flux of ≈106 cm-2 s-1 at ≈1 m distance from the tokamak center, and the discrepancy between the diamond detector and the activation foils is ≈25%.

A fast numerical method for calculating SPND space charge effect at steady state

To address the issue of low efficiency and long computation times in calculating the space charge effect in Self-Powered Neutron Detectors (SPNDs), we developed a fast and efficient numerical method to calculate the steady-state electric fields in SPND insulators. Previous calculations have shown that even when the electric field in the SPND insulator reaches 1 GV/m, its effect on electron transport is negligible. Therefore, we assume that the electric field has a negligible effect on electron transport. Based on this assumption, we developed a one-step numerical method for calculating the steady-state electric field in the insulator. This fast method is based on the charge conservation equation in equilibrium, thus requiring only a single charge deposition result without an electric field to obtain the distribution of the electric field under steady-state conditions. We validated our method by comparing it with precise iterative calculation results and experiments. The computational results indicate that, for three typical experimental scenarios, the fast method only takes up to one percent, or even less, of the time required by the iterative method. At the same time, the Mean Relative Error (MRE) in the electric field distribution between the fast method and iterative calculations are 1.48%, 0.31%, and 5.12%, respectively; whereas the relative errors in sensitivity calculations based on the electric field compared to iterative calculations are all less than 2%. Therefore, the fast method can significantly reduce computation time and ensure sufficient accuracy of steady state electric field distribution when the electric field is less than 1 GV/m. The introduction of this method has made it possible to conduct space charge effect assessments and precise sensitivity calculations for the placement of detectors throughout the entire reactor core.

Spectroscopic performance of Low-Gain Avalanche Diodes for different types of radiation

LGADs (Low-Gain Avalanche Diodes or Detectors) are a type of silicon Avalanche Photo-Diodes originally developed for the fast detection of minimum ionizing particles in high-energy physics experiments. Thanks to their fast timing performance, the LGAD paradigm enables detectors to accurately measure minimum ionizing particles with a timing resolution of a few tens of picoseconds. Such a performance is due to a thin substrate and the presence of a moderate signal gain. This internal gain of a few tens is enough to compensate for the reduced charge deposition in the thinner substrate and the noise of fast read-out systems. While LGADs are optimized for the detection of minimum ionizing particles for high-energy particle detectors, it is critical to study their performance for the detection of different types of particle, such as X-rays, gamma-rays, or alphas. In this paper, we evaluate the gain of three types of LGADs: two devices with different geometries and doping profiles fabricated by Brookhaven National Laboratory, and one fabricated by Hamamatsu Photonics with a different process.Since the gain in LGADs depends on the bias voltage applied to the sensor, pulse-height spectra have been acquired for bias voltages spanning from the depletion voltage up to the breakdown voltage. The signal-to-noise ratio of the generated signals and the shape of their spectra allow us to probe the underlying physics of the multiplication process.

Gate breakdown induced stuck bits in sub-20 nm FinFET SRAM

This paper discusses the stuck bits induced by the gate breakdown of PMOS in the sub-20 nm FinFET static random access memory (SRAM) device. After the heavy-ion experiment, several stuck bits are in the FinFET SRAM matrix, which cannot be set or reset. To investigate the factors that caused the stuck bit, we perform the electrical failure analysis (EFA) to measure the electric characteristics of the transistors in the stuck bits and normal cells separately. The measurement results show a clear gate breakdown at the PMOS pull-up (PPU) transistor in all of the measured SRAM cells. Meanwhile, the SPICE simulation based on the EFA results verifies the impact of the damaged PPU. Finally, considering all of the phenomena, the charge deposition from single events is the major mechanism that causes the stuck bits in FinFET SRAM. The experiment results alert a potential gate breakdown risk in the ultra-high-density FinFET SRAM applied in the space environment.

Effective removal of uranium (VI) with a SDBS doped PPy-SUS304 electrode from alkaline wastewater using electrodeposition strategy

The immobilization of uranium in nuclear wastewater is of paramount importance for environmental and human health. However, there is a paucity of research on the immobilization of uranium in alkaline wastewater, particularly with regards to the application of novel electrodes. This article presents the utilization of an electrochemically polymerized polypyrrole stainless steel (PPy-SUS304) electrode for the effective electrochemical deposition and removal of uranium from alkaline wastewater containing uranium. According to the electrodeposition results, the uranium deposition efficiency of the novel electrode reached 96.82 %, with a uranium deposition rate of 0.048 mg U/(h·cm2) and a charge efficiency of 0.055 mg U/C. These findings demonstrate the successful electrochemical reduction of UO2(CO3)34- in alkaline uranium-containing wastewater using the novel electrode, resulting in improved charge deposition efficiency. The electrode surface products were investigated using scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), and X-Ray Photoelectron Spectroscopy (XPS). The SEM and EDS results demonstrate the formation of a uniform PPy film on the surface of SUS304. In addition, the White light interferometer (WLI) test reveals that the PPy-SUS304 electrode exhibits increased roughness compared to the SUS304 electrode. The XPS results revealed that the electrode surface products of PPy-SUS304 were actually U compounds constituted of U(IV) oxides or hydroxides. This study provides a new perspective for the development of novel electrodes to suppress side reactions and efficiently recover uranium from alkaline uranium-containing wastewater.

How Charges Separate when Surfaces Are Dewetted.

Charge separation behind moving water drops occurs in nature and technology. Yet, the physical mechanism has remained obscure, as charge deposition is energetically unfavorable. Here, we analyze how a part of the electric double layer charge remains on the dewetted surface. At the contact line, the chemical equilibrium of bound surface charge and diffuse charge in the liquid is influenced by the contact angle and fluid flow. We summarize the mechanism in an analytical model that compares well with experiments and simulations. It correctly predicts that charge separation increases with increasing contact angle and decreases with increasing velocity.

Toward a multi-layer micro-structured detector for high-energy electron radiotherapy.

The use of electron beams has been rekindled by the advent of ultra-high-dose rate radiotherapy (FLASH) and very high energy electrons (VHEE). The need for development of novel technology for beam monitoring and dosimetry of such beams is of paramount importance prior to their clinical translation. In this work we explore the potential of a multi-layer nanoporous aerogel High-Energy-Current (HEC) detector as a dosimeter for electron beam. The detector does not suffer from radiation damage or signal saturation, making it suitable for very-high-dose-rate applications. Standard dose rates and energies are used to establish reference for FLASH and VHEE. We explore detector response to electron energy and residual range both experimentally and computationally. Multilayer HEC detectors were constructed using 1×-10× basic modules of Aluminum(Al)_aerogel(A)_Tantalum(Ta) with 10-70 µm layer thicknesses. Signals are collected from all electrodes (3-21, depending on module multiplicity) with zero external voltage bias. Measurements are acquired as a function of depth(z) in water equivalent plastic using Varian TrueBeam for energies E=6,9,12,15 MeV (SAD=105cm, 6×6 cone, 1000 MU/min). Computational simulations of identical detector geometries are performed using the 1D deterministic code CEPXS/ONEDANT. Additionally, percent-depth-doses PDD(z), measured with diode in water, are used to explore the response of HEC for various energies and residual ranges. The current measured from Ta electrodes resembles the shape of deposited charges in water and it is proportional to the derivative of the clinical PDD corrected for contribution from photon contamination. The signal is positive on the surface, and it decreases with depth reaching a negative local minimum at z=R50, before increasing again, reaching zero at about the practical range z=Rp. In contrast, the signal from Al electrodes is shaped like the electron PDD(z) shape but with lower signal at the surface and higher bremsstrahlung tail. By subtracting the signal from Ta and Al electrodes we obtained a curve resembling PDD(z,E) after Bremsstrahlung contamination correction. Multi-layer HEC sensors exhibit characteristic responses to electron beams that are unlike responses of ion chambers or diodes. Since the sensor structures are sensitive to electronic disequilibrium, high-Z electrodes give a signal proportional to the charge deposition pattern and can be modeled using the derivative of PDD(z).

Research on a Neutron Detector with a Boron-Lined Multilayer Converter

3He is a splendid neutron detection material due to its high neutron reaction cross section, gaseous state, and nonelectronegative and nonpoisonous nature. With the worldwide problem of the “3He supply crisis” arising, boron-lined gaseous neutron detectors are being widely used in neutron detection to replace 3He neutron detectors. In this work, to reduce the scattering neutron background coming from the substrate of a boron-lined neutron detector in the application of neutron scattering, a new design of the boron-lined gaseous neutron detector composed of a boron-lined multichip converter and a multiwire proportional chamber was proposed. The electron drift efficiency matrix simulated by Garfield++ (Version 2023.4) and the values and positions of electron energy deposition simulated by Geant4 were obtained. The α, 7Li, and total charged particle energy deposition spectra were acquired via coupling calculations of the electron drift efficiency matrix and the values and positions of electron energy deposition, and the width of the slit was selected as 3 mm. The boron-lined multilayer converter neutron detector (BMCND) was tested using a 241Am–239Pu mixture α source, and the total count rate of α charged particles was measured as 599.5 s−1, which is 89% of the theoretical α particle emission rate of 672.9 s−1. The drift voltage experiments showed that 1200 V is enough to acquire a relatively ideal count, and a 2500 V drift voltage was confirmed, considering the higher count and instrument safety. We also performed the neutron detection experiments using a photo-neutron source, and a characteristic spectrum shape of “two stairs” was measured. When borated polyethylene was used to shield the BMCND, the detected total count decreased while keeping the characteristic spectrum shape, demonstrating that the BMCND was equipped with the ability to detect neurons, indicating that BMCNDs have the potential to be an outstanding 3He alternative neutron detector.

Control of spontaneous charging of sliding water drops by plasma-surface treatment

Slide electrification is the spontaneous separation of electric charges at the rear of water drops sliding over solid surfaces. This study delves into how surfaces treated with a low-pressure plasma impact water slide electrification. Ar, O2, and N2 plasma treatment reduced the drop charge and contact angles on glass, quartz, and SU-8 coated with 1H,1H,2H,2H-perfluoroctyltrichlorosilane (PFOTS), and polystyrene. Conversely, 64% higher drop charge was achieved using electrode-facing treatment in plasma chamber. Based on the zeta potential, Kelvin potential, and XPS measurements, the plasma effects were attributed to alterations of the topmost layer's chemistry, such as oxidation and etching, and superficially charge deposition. The surface top layer charges were less negative after electrode-facing and more negative after bulk plasma treatment. As a result, the zeta potential was less negative after electrode-facing and more negative after bulk plasma treatment. Although the fluorinated layer was applied after plasma activation, we observed a discernible impact of plasma-glass treatment on drop charging. Plasma surface modification offers a means to adjust drop charges: electrode-facing treatment of the fluorinated layer leads to an enhanced drop charge, while plasma treatment on the substrate prior to fluorination diminishes drop charges, all without affecting contact angles or surface roughness.

Advances in Particle-In-Cell Modeling of Low-Temperature Plasma Ion Sources

Ion sources that use low-temperature plasma (LTP) discharges are used in a variety of applications, including ion implantation, mass spectrometry, and plasma processing. In recent years there has been a growing interest in using particle-in-cell (PIC) modeling to improve the performance and optimization of LTP-based ion sources. PIC modeling is a powerful tool for simulating the dynamics of plasmas because it accurately models the effects of self-consistent fields, charge deposition, plasma chemistry, magnetic confinement, and accurate sheath physics. However, PIC simulations can be computationally demanding, especially for 3D systems.We present new advances in PIC modeling of LTP ion sources. We focus on two key challenges: 1. Efficient and accurate modeling of plasma chemistry: Plasma chemistry is a complex process that can have a significant impact on the performance of LTP ion sources. We demonstrate using global models to reduce the computational cost of plasma chemistry simulations, and diagnostics for understanding the physics of those reactions. 2. Energy-conserving PIC models: PIC simulations typically require a fine spatial grid in order to resolve the Debye length. This can be computationally expensive, especially for 3D systems. We present a new energy-conserving PIC model implementation that allows us to perform simulations without resolving the Debye length. We validate these methods on two different types of LTP ion sources: a Bernas source and a Penning source. Our results show that these methods can significantly improve the efficiency and accuracy of PIC simulations of LTP-based ion sources.

Self-pulsing of dielectric barrier discharges at low driving frequencies

This paper investigates the self-pulsing of dielectric barrier discharges (DBDs) at low driving frequencies. In particular, (a) the dependence of current on the product pd of gas pressure p and the gas gap length d, (b) the effects of lossy dielectrics (in resistive discharges) and large dielectric permittivity (in ferroelectrics) on current dynamics, (c) the transition from Townsend to a dynamic capacitively coupled plasma (CCP) discharge with changing pd values, and (d) the transition from Townsend to a high-frequency CCP regime with increasing the driving frequency. A one-dimensional fluid model of argon plasma is coupled to an equivalent RC circuit for lossy dielectrics. Our results show multiple current pulses per AC period in Townsend and CCP discharge modes which are explained by uncoupled electron–ion transport in the absence of quasineutrality and surface charge deposition at dielectric interfaces. The number of current pulses decreases with an increasing applied frequency when the Townsend discharge transforms into the CCP discharge. The resistive barrier discharge with lossy dielectrics exhibits Townsend and glow modes for the same pd value (7.6 Torr cm) for higher and lower resistances, respectively. Finally, we show that ferroelectric materials can amplify discharge current in DBDs. Similarities between current pulsing in DBD, Trichel pulses in corona discharges, and subnormal oscillations in DC discharges are discussed.

Characteristics of Surface Charge Accumulation on Spacers and Its Influencing Factors

Charge accumulation usually happens on the surface of spacers under DC operation, which is susceptible to inducing surface flashover. In order to explore the surface charge accumulation mechanisms and the influences of dielectric conductivity, gas ion mobility, and temperature field on the surface charges, a time-varying charge density model at the gas–solid interface of spacers was established. The results of the simulation show that the discontinuity of the current density between the spacer bulk side and the gas ion flow is the fundamental reason for the charge accumulation on the spacer surface. Additionally, the value of current density fluxes at the interface continues to decrease with the change of the electric field, and the progress of charge transfer gradually stabilizes. Moreover, the dielectric conductivity directly affects the charge accumulation process, and there is a critical conductivity in which the effect of charge conduction in dielectrics counteracts that of gas-phase charge deposition, theoretically. When the conductivity is higher than the critical conductivity, the solid-side charge conduction is the main source of the surface charge accumulation, while the gas-phase charge deposition on the gas side plays a dominant role when the conductivity is lower than the critical conductivity. The charge accumulation is not significantly affected by gas ion mobility when the temperature is evenly distributed. However, under the temperature field with gradient distribution, the current density fluxes at the interface change, causing the polarity reverse of the accumulated charge. In the high-temperature region, the volume current density surges simultaneously with the conductivity, leading to a higher density of surface charge accumulation. Lastly, the design of spacers needs to keep the current densities on both sides of the interface as similar as possible in order to avoid excessive charge gathering in localized areas.

Analogous Charging Effect of Surfactant-Pesticide Spray Jet on Droplet Characteristics and Deposition on Hydrophobic Leaf Surfaces

An induction charging principle had been applied to enhance spray droplet characteristics and quantity deposition on hydrophobic abaxial-adaxial leaf surfaces from pesticide EC Glyphosate [C3H8NO5P] and surfactant Silwet L-77 [C13H34O4Si3] formulations. A nozzle cap containing two electrodes (spacing at 9 mm apart) was used to superpose charges to spray droplets under applied voltages of 2–12 kV in an electric field (E) of 8.9 × 105 V/m. From a tee-jet flat fan (TP11004VS) nozzle tip fitted into the electrode cap and positioned at 60 cm high above targeted Brassica campestris leave surfaces, the spray droplets were directed onto the leaves at a liquid flow pressure of 4 bar and travelling speed of 2 m/s. The measurements were done using Keithsley picoammeter to quantify spray chargeability (CMR), droplet sizes by lesser particle size analyzer (LPSA) and deposition on leaf surfaces by high-speed camera. In effect, droplet sizes of EC, L-77 and EC + L-77 decreased with an increasing applied voltage. The CMR of L-77 was lower than EC and highest for EC + L-77 composite solution. Based on Image analysis of droplets density per leaf area, maximum exposure of adaxial leaf surfaces intercepted many charged spray droplets than abaxial surfaces. As regressed, the quantity of charged spray deposition from EC + L-77 formulation was highest at both adaxial (approx. 27.44 Qd/cm2) and abaxial (approx. 5.57 Qd/cm2) hydrophobic leaf surfaces than EC of 26.12: 3.19 Qd/cm2 and L-77 of 24.80: 2.53 Qd/cm2, respectively. Also, contact angle, Theta E, of charged spray droplets was smaller than Theta C on adaxial than abaxial leave surfaces, a phenomenon attributed to high chemo-electrical properties of formulations that aided the direct flight, coiling and deposition of droplets in order of EC > EC + L-77 > L-77. Generally, there was no observable droplet rebound; hence, surfactant-pesticide composite spraying is considered suitable for electrostatic application in plant protection technology. Therefore, for effective application, charged droplets from glyphosate EC in silwet L-77 solution should be recommended, as it provides optimum droplet sizes, chargeability, contact angle and deposition on hydrophobic leave surfaces.

Analytical and numerical modelling of the electrostatic behaviour of highly insulating materials in the time domain

The usual response of an insulator subjected to a voltage step involves time power laws. We present here mathematical tools allowing to calculate this time domain response in open circuit after an initial charge deposit, within the framework of linear systems theory, using linear fractional transfer functions. In the time domain, the inverse Laplace transform of the data taken from the frequency domain leads to Mittag-Leffler functions, generalizing the Debye exponential response to an extended fractional α-order response. The open-circuit boundary conditions are different from the closed-circuit ones. We nevertheless demonstrate that using a transfer function deduced from the Cole-Cole response in closed-circuit, a precise analytical formula of the potential decay after an initial charge deposit may be established, and a numerical computation of this decay may be performed using easily available software. Applying the superposition principle, the voltage return following a brief short circuit may also be deduced. Experimental results are presented and the limits of the superposition principle applied to real materials are discussed.

Elimination of gas entrapment in droplet-based 3D printing by induced electric-field

Gas entrapment during droplet deposition may induce pinhole defects in droplet-based 3D printing. However, achieving effective suppression of gas entrapment is challenging given that gas entrapment behavior is the physical essence of droplet impact. Inspired by that charged droplets will be deformed in the electric field, a method of suppressing gas entrapment by weakly charging the droplet was proposed. Here, a numerical model is developed to systematically investigate the gas entrapment behaviors during neutral droplet and charged droplet deposition. Results show that the electric field will be induced before the instant of droplet impact on the substrate, which fundamentally changes the gas entrapment behavior. Moreover, the competition mechanism between Maxwell stress and lubrication pressure during droplet deposition is revealed, and the pressure inside and outside the droplet bottom profile is quantified. Compared with the neutral droplet, the additional electric stresses act against the lubrication pressure, which increases sharply before the droplet touches the substrate. When the charge level reaches a critical value, the electric stresses are slightly stronger than the lubrication pressure at the bottom center, and the decrease rate of electric stresses along the horizontal distance r is higher than that of gas film pressure, leading to a central touchdown with residue concentric circle gas rings. Furthermore, the evolution of phase fraction, velocity field, and pressure field during droplet deposition with different charge level is investigated comprehensively. Based on this, the dimensionless scale of critical charge level to fundamentally eliminate gas entrapment is obtained. This work may provide new insights into various applications involving droplet deposition, such as eliminating pinhole defects in droplet-based additive manufacturing.