Non-uniform Charging Research Articles

X-ray-induced piezoresponse during X-ray photon correlation spectroscopy of PbMg1/3Nb2/3O3.

X-ray photon correlation spectroscopy (XPCS) holds strong promise for observing atomic-scale dynamics in materials, both at equilibrium and during non-equilibrium transitions. Here an in situ XPCS study of the relaxor ferroelectric PbMg1/3Nb2/3O3 (PMN) is reported. A weak applied AC electric field generates strong response in the speckle of the diffuse scattering from the polar nanodomains, which is captured using the two-time correlation function. Correlated motions of the Bragg peak are also observed, which indicate dynamic tilting of the illuminated volume. This tilting quantitatively accounts for the observed two-time speckle correlations. The magnitude of the tilting would not be expected solely from the modest applied field, since PMN is an electrostrictive material with no linear strain response to the field. A model is developed based on non-uniform static charging of the illuminated surface spot by the incident micrometre-scale X-ray beam and the electrostrictive material response to the combination of static and dynamic fields. The model qualitatively explains the direction and magnitude of the observed tilting, and predicts that X-ray-induced piezoresponse could be an important factor in correctly interpreting results from XPCS and nanodiffraction studies of other insulating materials under applied AC field or varying X-ray illumination.

Full cycle, self-consistent, two-dimensional analysis of a packed bed DBD reactor for plasma-assisted splitting: spatiotemporal inhomogeneous, glow to streamer to surface discharge transitions

We investigate the full-cycle operation of a coaxial Packed Bed Dielectric Barrier Discharge (PB-DBD) reactor operating in pure . The reactor is packed with high permittivity dielectric rods and is analyzed with a two-dimensional (2D) self-consistent plasma model. We show that the PB-DBD operation is governed by both glow and volume/surface streamer discharges, forming alternatively and non-uniformly inside the gas volume. The presence and surface charging of the dielectric rods and dielectric layer is crucial for the initiation, propagation, annihilation and afterglow of these microdischarges. Our calculations show maximum electron and densities in the order 1020 m−3, an average discharge power of 353.42 W m−1 in the first cycle, microdischarge peak currents in the order of 50–400 A m−1, total half-cycle plasma charge of around 6 µC m−1, which compare well with experimental findings. Dominant negative ions are found to be . CO molecules and O atoms are mainly formed during the MDs development and the streamer-surface ionization waves. Molecular oxygen () is preferentially formed during the glow, current-decaying and afterglow phase of each microdischarge. The spatially average reduced electric field inside the reactor lies in the 20–100 Td range. Each MD, presents distinct non-uniform and non-repeatable glow and volume/streamer discharges owed to the non-uniform surface charging processes which dictate the complex spatial distribution of produced neutral (and ion) species. These detailed results shed light on crucial, largely non-uniform plasma spatiotemporal characteristics that can help design efficient PB-DBD reactors for splitting and beyond, while emphasizing the important insights obtained by 2D simulations which can not be captured with 0D-global or 1D models.

XPS study of iodine and tin doped Sb2S3 nanostructures affected by non-uniform charging

X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements are used for investigating incorporation of iodine and tin into the stibnite (Sb2S3) lattice, as well as for determining surface composition and structure, respectively. The XRD analysis revealed the visible presence of a single phase, that of pure orthorhombic Sb2S3 structure. XPS survey spectra confirmed the presence of expected elements (Sb, S, Sn and I) at the surface of corresponding samples. Since the bonding identification was hindered by non-uniform charging of samples during acquiring the photoelectron spectra, a novel approach for the analysis of high resolution spectra was proposed and successfully implemented. XPS results showed that surface composition of the non-doped sample coincides with that of the bulk, while doping strongly affects surface of the samples. Sn-doped sample appears to be prone to surface oxidation. The presence of Sb2S3, Sb2O3, SnS2 and Sn(0) phases at the surface was revealed. Strong segregation of antimony was observed in the I-doped Sb2S3 sample. Iodine is also present at the surface in the form of the SbI3 phase, while the detected sulphur signal most probably corresponds to S atoms from unaltered deeper layers.

A non-uniform charging scheme to decipher charge state propensities measured in nano-cluster ionization

A non-uniform charging scheme to decipher charge state propensities measured in nano-cluster ionization

On the Discharge Transport Mechanisms Through the Dielectric Film in MEMS Capacitive Switches

A method that allows the investigation of discharge transport mechanism in dielectric films used in MEMS capacitive switches or MIM capacitors or even bare dielectric films is presented. The method is based on monitoring the dielectric film surface or MIM top electrode potential decay rate and the dependence of conductivity on surface potential. The method has been applied in MEMS and MIMs with simultaneously deposited dielectric film to confirm the closeness of transport data in MIM and MEMS devices. The impact of non-uniform charging on local discharge rate and different dielectric film stoichiometry has been also assessed. Finally, the effect of surface leakage due to environment humidity has been also investigated. [2019-0159].

Sulfur heat transfer behavior for uniform and non-uniform thermal charging of horizontally-oriented isochoric thermal energy storage systems

Elemental sulfur is a low-cost, chemically stable thermal storage medium suitable for many medium to high temperature applications. In this study, we investigate the heat transfer behavior of sulfur, isochorically stored in a horizontally-oriented thermal storage element (steel tube) using experimental, analytical, and computational methods. The sulfur container was uniformly and non-uniformly heated along its axis from 50 to 600 °C to simulate the potential operating conditions for the full-scale thermal energy storage systems. The results of the study reveal distinct sulfur heat transfer mechanisms based on the temperature range and mode of thermal charging. For temperatures from 50 to 200 °C, the sulfur heat transfer behavior is governed by two primary mechanisms; 1) solid–liquid phase change, and 2) sulfur viscosity that varies strongly with temperature. From 200 to 600 °C, the buoyancy-driven natural convection is the dominant heat transfer mechanism and facilitates significantly high thermal charge rates. For axially non-uniform thermal charging, the axial temperature gradient induces natural convection along the axis that rapidly redistributes the thermal energy within the sulfur mass. Such axial convection has a strong impact on the thermal characteristics, including thermal charge/discharge rate and exergetic efficiency of the thermal storage systems. These observations and the high-fidelity computational model used in this study provide important means to identify the design parameters and operating conditions for which sulfur-based thermal energy storage (SulfurTES) systems will provide desirable thermal performance at a low thermal storage cost.

High C-Rate Differential Expansion and Voltage Model for Li-Ion Batteries

The differential voltage analysis (DVA) is one of the conventional approaches for estimating capacity degradation. The phase transitions in the graphite electrode emerge as observable peaks in the differential voltage. The DVA method utilizes these peaks for estimating battery’s capacity. Unfortunately, at higher C-rates (above C/2) the peaks flatten, and their locations become unobservable. Hence the capacity estimation becomes highly uncertain. Li-ion batteries also expand (contract) during charging (discharging) in repeatable patterns. Thus, the derivative of cell expansion is also used for identifying phase transitions. The peaks in the voltage derivative curve and the second derivative of the expansion curve correspond to the same phase transitions in the material [1]. Unlike the differential voltage, the peaks are observable up to 1C rate in the differential expansion curve, which makes the differential expansion an excellent method for capacity estimation during fast charging scenarios (above C/2). To understand why that is the case, and at the same time develop a model-based estimator a multi-particle electrochemical model is developed. The electrochemical model is primarily based on the well-known Doyle Fuller Newman (DFN) model. The inclusion of electrodes with multiple materials is done in [2], and the approach to modeling multiple sized particles is analogous to the models for multi-material electrodes. The particles are in a parallel configuration, and similar to the single particle model (SPM) the molar flux and solid concentration are independent of location [3]. However, the electrolyte dynamics are considered in the model. The model also includes a particle expansion model and an energy balance model. Currently, the temperature is only coupled to the thermal expansion model. The cell under consideration in this study is a 5 Ah graphite/NMC pouch cell fabricated at the University of Michigan Battery Lab. A fixture was designed to measure the mechanical response of the cell. The expansion was measured using a displacement sensor (Keyence, Japan) mounted on the top plate, and a battery cycler (Biologic, France) was used for measuring the voltage. The fixture was installed inside a climate chamber with the temperature set to 25˚C. The cell was charged with a constant current (CC) from the fully discharged state at different rates (C/20, C/10, C/5, C/2.5, 1C, and 2C) up to 4.2 V, followed by a constant voltage (CV) period until (I<C/50), followed by a pause of 3 h. The thermal tests were performed to characterize the thermal expansion and cooling behavior of the fixture. The expansion was also monitored during these tests and used in thermal expansion coefficient estimation. Furthermore, to measure the potential of graphite and NMC electrodes, coin cells were built. The Li/NMC (Li/graphite) coin cell was cycled at C/50 between 2.8 and 4.35 V (0.005 and 1.0 V). The lattice expansion data was taken from literature for graphite and NMC. Figure 1(a) shows the overall model structure. Furthermore, Fig. 1(b) presents the voltage and expansion derivatives; from this figure, the aforementioned smoothing effect of the voltage derivative is seen. Note that the voltage peaks are unobservable at 1C rate. The voltage and expansion derivatives for the C/5 and 1C are selected to showcase the smoothing effect of the model, and they are depicted in Fig. 1(c) and (d). Finally, Fig. 1(e), (f), and (g) show the model prediction together with the data for voltage, expansion, and temperature rise, respectively. The multi-particle model with different particle sizes results in a distribution of concentration among the particles. This is simulating the non-uniform charging of particles that can happen at higher rates, which is causing the smoothing effect. Furthermore, the reason for the observability of the peaks at higher rates in expansion is that first, the changes between lattice parameters of two different phases are more significant compared to their voltage, and second, the voltage is a function of the surface concentration, while the expansion is a function of the concentration curve in the particle.

Surface charging and its effects on DC flashover strengt of insulating materials

Surface charging is a common occurrence during service for all HV insulators as well as live-line tools during live-line maintenance work. The main sources of non-uniform charging are corona discharges from nearby and/or direct contact with energized objects and cloth wiping by tribo-charging effect. This paper focuses on studying the DC charging characteristics of three different insulating materials and the flashover performance of such pre-charged insulating materials. The samples used are cylinders of 130 mm length with different diameters. Surface charging by cloth wiping is found to be much more than that of corona discharges from energized objects. Surface charges take more than four hours to decay by 80%. Moreover, surface charges can increase the positive and negative flashover voltages of pre-charged samples by up to 13%. Mitigation methods to improve the flashover performance of insulating materials are identified. The research on surface charging forms hypotheses and recommendations which may improve the live-line maintenance procedures in ways that protect live-line workers from accidents.

Redefinition of the self-bias voltage in a dielectrically shielded thin sheath RF discharge

In a geometrically asymmetric capacitively coupled discharge where the powered electrode is shielded from the plasma by a layer of dielectric material, the self-bias manifests as a nonuniform negative charging in the dielectric rather than on the blocking capacitor. In the thin sheath regime where the ion transit time across the powered sheath is on the order of or less than the Radiofrequency (RF) period, the plasma potential is observed to respond asymmetrically to extraneous impedances in the RF circuit. Consequently, the RF waveform on the plasma-facing surface of the dielectric is unknown, and the behaviour of the powered sheath is not easily predictable. Sheath circuit models become inadequate for describing this class of discharges, and a comprehensive fluid, electrical, and plasma numerical model is employed to accurately quantify this behaviour. The traditional definition of the self-bias voltage as the mean of the RF waveform is shown to be erroneous in this regime. Instead, using the maxima of the RF waveform provides a more rigorous definition given its correlation with the ion dynamics in the powered sheath. This is supported by a RF circuit model derived from the computational fluid dynamics and plasma simulations.

Comparative study of image contrast in scanning electron microscope and helium ion microscope.

Images of Ga+ -implanted amorphous silicon layers in a 110 n-type silicon substrate have been collected by a range of detectors in a scanning electron microscope and a helium ion microscope. The effects of the implantation dose and imaging parameters (beam energy, dwell time, etc.) on the image contrast were investigated. We demonstrate a similar relationship for both the helium ion microscope Everhart-Thornley and scanning electron microscope Inlens detectors between the contrast of the images and the Ga+ density and imaging parameters. These results also show that dynamic charging effects have a significant impact on the quantification of the helium ion microscope and scanning electron microscope contrast.

A model for the non-uniform contact charging of particles

If a particle is in contact with another solid electric charge may be exchanged. Previous experimental observations clearly prove that the amount of exchanged charge does not only depend on the charge carried by the particle prior to the contact but also on its local distribution on the particles surface. However, most existing modeling approaches utilize the assumption of a uniformly charged particle. In the present paper we propose a new model which accurately accounts for the charge distribution on the particles surface during particle-wall and inter-particle collisions. Further, the results obtained with the new model are compared to data of single particle charging experiments. Moreover, we implemented the model in a Computational Fluid Dynamics (CFD) simulation of powder pneumatically transported in a pipe. We show that the charging behavior of the powder is quantitatively and qualitatively different if a non-uniform charge distribution is taken into account.

Deformation and Non-uniform Charging of Toner Particles: Coupling of Electrostatic and Dispersive Adhesion Forces

Both electrostatic and dispersive (van der Waals) forces contribute to particle adhesion, which has a significant effect on toner transfer in the electrophotographic process. Several approaches to adhesion measurements have yielded a large range of results for a variety of particle and environmental conditions. We present adhesion measurements taken in different environments using the metered air pulse method. They yield significantly different removal forces as a function of temperature for the same average particle charge. Particle deformation due to a combination of changes in particle stiffness with temperature and compressive electrostatic forces can predict the resulting adhesion increase. The morphology change is one of several factors which can contribute to the measured adhesion, which is significantly higher than values obtained by considering only the charged particle monopole and its image. Additionally, non-uniform charging in controlled adhesion experiments provides further muddling between the electrostatic and dispersive forces. This result is due to the electrostatic force having a component which is independent of the nominal charge under certain conditions. We find that the adhesion forces can be fully cubic with respect to the average particle charge, and that the components of the adhesion force may be much more difficult to decouple than previously thought.

充电不均匀对脉冲形成系统输出方波脉冲平顶的影响

充电不均匀对脉冲形成系统输出方波脉冲平顶的影响

Effect of Asymmetric Channel on Charging Behavior of 22-nm Quantum-Dot Floating-Gate Flash Memory Cell

The need of high density, high speed, and reliable memories is leading toward the development of new approaches such as quantum-dot floating gates (QDFGs), use of high- $k$ dielectrics as tunneling/control gate oxides, and metal-gate technology. QDFG 22-nm Flash memory cells based on these new approaches are investigated through process and device simulations using Synopsys Technology Computer-Aided Design tools. Hafnium oxide is used as both tunneling and control gate oxides along with the metal control gate. As a solution to the nonuniform charging of QDFGs in these structures, asymmetric doping of the channel region is proposed. The effect of asymmetric channel doping on the charging behavior of QDFGs is studied, and the device characteristics are compared with symmetric channel counterpart. The simulation results confirm that the asymmetric channel device is faster in terms of programming and erasing time than the symmetric channel device.

Surface charging, discharging and chemical modification at a sliding contact

Electrostatic charging, discharging, and consequent surface modification induced by sliding dissimilar surfaces have been studied. The surface-charge related phenomena were monitored by using a home-built capacitive, non-contact electrical probe, and the surface chemistry was studied by X-ray photoelectron spectroscopy (XPS). The experiments were performed on the disk surface of a ball-on-rotating-disk apparatus; using a glass disk and a Teflon (polytetrafluoroethylene) ball arrangement, and a polyester disks and a diamondlike carbon (DLC) coated steel ball arrangement. The capacitive probe is designed to perform highly resolved measurements, which is sensitive to relative change in charge density on the probed surface. For glass and Teflon arrangement, electrical measurements show that the ball track acquires non-uniform charging. Here not only the increase in charge density, but interestingly, increase in number of highly charged regions on the ball track was resolved. Threefold increase in the number of such highly charged regions per cycle was detected immediately before the gas breakdown-like incidences compared to that of other charge/discharge incidences at a fixed disk rotation speed. We are also able to comment on the behavior and the charge decay time in the ambient air-like condition, once the sliding contact is discontinued. XPS analysis showed a marginal deoxidation effect on the polyester disks due to the charging and discharging of the surfaces. Moreover, these XPS results clearly indicate that the wear and friction (sliding without charging) on the surface can be discarded from inducing such a deoxidation effect.

In Situ Measurements of Potential, Current and Charging Current across an EDL Capacitance Anode for an Aqueous Sodium Hybrid Battery

This paper presents a novel method for obtaining in situ, through-thickness measurements of potential, current, charging current, and charge stored or discharged across capacitor and battery electrodes. Here we apply the method to an electrochemical double layer capacitance (EDLC) negative electrode for an aqueous sodium hybrid battery. In this approach, an electrode scaffold (ES) is used to directly measure the electric potential at discrete distances through the electrode under charging and discharging conditions. Finite difference methods are used to calculated local current and charging/discharging rates. The distributions obtained from these measurements are used to show non-uniform charging across an ultra-thick electrode intended for high area-specific energy storage in grid-scale energy storage applications. Using the ES we are able to gain insight into several complex phenomena that cannot be directly observed by other methods. For instance, we identify the portions of the electrode that are underutilized as well as the location of stray, parasitic currents.

Electrostatic force behavior of a nonuniformly charged particle on a planar dielectric solid

This paper presents the analysis of the electrostatic force on a nonuniformly charged dielectric particle resting on a dielectric solid. The purpose of the analysis is to clarify the force enhancement caused by the nonuniform charging when the particle is on the dielectric solid, and to examine the role of the dielectric solid on the force behavior in the presence of an external electric field. The method of images using multipoles is applied to electric field calculation, and the electrostatic force is determined from the Maxwell stress. The analytical results show significant force enhancement due to nonuniform charging even in the case where the particle and the dielectric solid have the same dielectric-constant value. However, with an externally applied electric field, the nonuniform charging also results in higher force magnitude for detachment of the particle from the plane in comparison with the case of uniform charging. The roles of the dielectric constants of the media involved on the electrostatic force behavior are investigated. Critical difficulty for the detachment is not found for a particle with dielectric constant equal to 4, which is remarkably different from the corresponding case of a particle lying on a conducting plane.

Observed Weak Electron Beam Discharge Driven Grain Acceleration/Accretion with Implications for Planet Formation

Work presented here addresses the issue of grain accretion, an essential yet poorly understood process in planetary system formation, linking the dynamically modeled steps of temperature-dependent condensation of gases after proto-sun gravitational collapse to coalescence of kilometer-size planetesimals into planets. The mechanism for grain accretion has proven difficult to model dynamically. Here, we attempt to test the thesis that the accretion process is electrostatically-driven by non-uniform charging of grains in a low discharge/weak field environment equivalent to periodic conditions in protoplanetary nebulae during solar discharge events such as flares. We simulate in the laboratory the behavior of grains in relationship to surfaces in such an environment. The nature of the observed disaggregation, repulsion, and acceleration of grains away from initial surfaces, and their reaggregation as coatings on surrounding oppositely charged surfaces, provide an empirical experimental basis for an electrostatically-driven model for grain behavior and accretion. Similar weak discharge processes in the protoplanetary disk solar nebula could give rise to increased grain acceleration and collisional compression induced surface coating, necessary conditions for increased accretion. The frequency, timing, and level of energetic output of the proto-sun would influence the effectiveness of such processes in developing stable aggregates, and the nature of the solar system that would result.

A computational model of a barrier discharge in air at atmospheric pressure: the role of residual surface charges in microdischarge formation

A two-dimensional (axially symmetric) computational model of the microdischarge formation in a barrier discharge for short (1–2 mm) gaps in air at atmospheric pressure is proposed. A non-homogeneous electric field, caused by a residual non-uniform charging of the dielectric barriers, is considered as an important reason for the filament formation by a Townsend mechanism. The ion–electron emission from the dielectric covering the cathode is treated as the principal secondary process; the secondary emission coefficient in the model is selected to be consistent with the Paschen voltage. For an applied sinusoidal voltage, this follows the microdischarge development on a microsecond scale. It is shown that even a slight inhomogeneity of the initial electric field leads to the formation of a narrow microdischarge channel.The two-dimensional dynamics of the radiation from a microdischarge for the case of the second positive and the first negative systems of nitrogen is simulated and compared with recent experimental data. The effects of the secondary emission coefficient and of a distribution of residual surface charges are investigated. It is shown that the level of inhomogeneity of the residual surface charge distribution does not affect the radius of the microdischarge channel, but affects its two-dimensional structure.The proposed model explains satisfactorily the experimental results for the velocity of the cathode-directed ionizing wave and the emission of the N2 second positive system from a microdischarge.

Nonuniform charging effects on ion drag force in drifting dusty plasmas

The nonuniform polarization charging effects on the ion drag force are investigated in drifting dusty plasmas. The ion drag force due to the ion-dust grain interaction is obtained as a function of the dust charge, ion charge, plasma temperature, Mach number, Debye length, and collision energy. The result shows that the nonuniform charging effects enhance the momentum transfer cross section as well as the ion drag force. It is found that the momentum transfer cross section and the ion drag force including nonuniform polarization charging effects increase with increasing the Mach number and also the ion drag force increases with increasing the temperature. In addition, it is found that the ion drag force is slightly decreasing with an increase of the Debye length.