Measurement Of Charge Distribution Research Articles

Extreme lightwave electron field emission from a nanotip

We report on sub-cycle terahertz light-field emission of electrons from tungsten nanotips under extreme conditions corresponding to a Keldysh parameter $\gamma_K\approx10^{-4}$. Local peak THz fields up to 40~GV/m are achieved at the apex of an illuminated nanotip, causing sub-cycle cold-field electron emission and acceleration in the quasi-static field. By simultaneous measurement of the electron bunch charge and energy distribution, we perform a quantitative test of quasi-static Fowler-Nordheim tunnelling theory under field conditions that completely suppress the tunnel barrier. Very high bunch charges of $\sim10^6$ electrons/pulse are observed, reaching maximum energies of 3.5~keV after acceleration in the local field. The energy distribution and emission current show good agreement with Fowler-Nordheim theory even in this extreme field regime. Extending this model to the single-shot regime under these conditions predicts peak electron distributions with a spectral purity of $10^{-4}$. THz field-induced reshaping and sharpening of the nanotip is observed, reducing the tip radius from 120~nm to 35~nm over roughly $10^9$ THz shots. These results indicate THz-driven nanotips in the extreme field limit are promising electron sources for ultrafast electron diffraction and microscopy.

Trapped fractional charges at bulk defects in topological insulators.

Topological crystalline insulators (TCIs) can exhibit unusual, quantized electric phenomena such as fractional electric polarization and boundary-localized fractional charge1-6. This quantized fractional charge is the generic observable for identification of TCIs that lack clear spectral features5-7, including ones with higher-order topology8-11. It has been predicted that fractional charges can also manifest where crystallographic defects disrupt the lattice structure of TCIs, potentially providing a bulk probe of crystalline topology10,12-14. However, this capability has not yet been confirmed in experiments, given that measurements of charge distributions in TCIs have not been accessible until recently11. Here we experimentally demonstrate that disclination defects can robustly trap fractional charges in TCI metamaterials, and show that this trapped charge can indicate non-trivial, higher-order crystalline topology even in the absence of any spectral signatures. Furthermore, we uncover a connection between the trapped charge and the existence of topological bound states localized at these defects. We test the robustness of these topological features when the protective crystalline symmetry is broken, and find that a single robust bound state can be localized at each disclination alongside the fractional charge. Our results conclusively show that disclination defects in TCIs can strongly trap fractional charges as well as topological bound states, and demonstrate the primacy of fractional charge as a probe of crystalline topology.

Inversion Algorithm for Surface Charge Distribution on Insulator in Shift-Invariant System Based on Constrained Least Square Filter

Surface flashover on an insulator caused by the charge accumulation at the gas–solid interface is one of the main reasons limiting the development of gas insulated equipment in high voltage direct current (HVDC) condition. Therefore, it is helpful to clarify the mechanism of surface flashover and surface charge behavior by measuring charge distribution with high accuracy. In this article, a surface charge inversion algorithm based on constrained least square filter (CLSF) is proposed for surface charge measurement in a shift-invariant system. By taking the image restoration technology as an analogy, the algorithm transfers matrix equation into frequency domain by 2-D Fourier transform, which significantly simplifies the computational process. Then the CLSF is used to suppress the noise signal and actualize the conduction from surface potential distribution to surface charge density distribution. The calculation process and accuracy of the algorithm are discussed in detail with the simulated examples, and the inversion performance of CLSF is compared with Wiener filter. At last, the effectiveness of the algorithm is verified by performing surface charge measurement and dust figure. This methodology gives an innovative idea of potential-charge transformation process with higher accuracy and stability, which benefits the development of surface charge measurement technology.

Measurement of Space Charge Distribution in Epoxy/Fullerene Nanocomposite at High Temperature under High DC Stress

Measurement of Space Charge Distribution in Epoxy/Fullerene Nanocomposite at High Temperature under High DC Stress

Correction to: Measurement of Sheet-like Space Charge Distribution and Signal Calibration of Insulator XLPE Using PEA Method

Correction to: Measurement of Sheet-like Space Charge Distribution and Signal Calibration of Insulator XLPE Using PEA Method

Space Charge Distribution Measurement in FEP Film Irradiated by Proton

Space Charge Distribution Measurement in FEP Film Irradiated by Proton

Measurement of Sheet-like Space Charge Distribution and Signal Calibration of Insulator XLPE Using PEA Method

Long-distance power transmission requires durable and high-performance cables with insulators resistant to dielectric breakdown. However, space charge can cause dielectric breakdowns by affecting the electrical characteristics inside the insulator as it is injected, generated, or moved inside the insulating materials. In this study, the sheet-like space charge distribution of the insulator cross-linking polyethylene (XLPE) was measured using the pulsed electro acoustic (PEA) method. As compared to the existing method, a more convenient method was designed and produced using NI’s PXI System and LabVIEW software. Furthermore, a signal calibration program was developed to correct the distortions of the measured signals. The accuracy and reliability of the space charge distribution signals were improved by correcting the distortions of the signals.

Broken Insulator Effects on Charge Distribution Measurement along Suspension Insulators

In the early years of power system network, porcelain and glass were used and still continuously serve the overhead lines to the present time. Obviously, they can provide distinction services over a long period of time. In spite of that, one or two of the insulators in the suspension may be damaged due to some cases yet the suspension insulator is believed can still be used for a certain amount of time. By studying some research from previous works, it is accepted that the different properties of porcelain and glass type had made these insulators vary in their respective capabilities to serve overhead lines. This paper endeavours the distribution of charge for the porcelain suspension insulator using chamber method. Finite element software particularly QuickfieldTM was used in simulation purpose to validate the experimental results. Similar patterns of charge distributions were acquired for both experimental and simulation works.

Measuring the bipolar charge distribution of nanoparticles: Review of methodologies and development using the Aerodynamic Aerosol Classifier

A review of methodologies to measure the bipolar charge distribution of nanoparticles is completed, including their advantages/disadvantages and sequential development. This summary also provides context for a new development, which uses an Aerodynamic Aerosol Classifier (AAC) and Differential Mobility Analyzer (DMA) in tandem for a similar purpose. It is demonstrated that the tandem AAC-DMA system overcomes some significant limitations of the previous methodologies, such as multiply-charged particle artefacts and low measurement signals. The tandem AAC-DMA methodology also has the sensitivity to detect other charging phenomena, such as the effects of different sample flow rates through the charger, free-ions downstream of the charger, the inlet insert on the 85Kr charger and different particle chargers (x-ray, old 85Kr and new 85Kr).The charge fractions of the particles at low-flow (0.6 L/min) through the new 85Kr charger agreed well (average absolute difference of 0.007) with widely-used charging theory. However, significant deviations from theory (up to a 0.044 difference in charge fractions) were found with a higher sample flow rate (1.2 L/min), with different exposure times to free-ions downstream of the charger, or with the inlet insert on the new 85Kr charger. It was found that regardless of flow rate, a soft x-ray charger resulted in charge fractions which deviated significantly from theory (up to a 0.084 difference in charge fractions), producing higher fractions of positively charged particles and lower fractions of negatively charged particles relative to theory. All of these deviations are likely due to the simplifying assumptions made by the charging theory. Therefore, rigorous measurement of particle charge distributions are necessary for accurate aerosol characterization, such as standard SMPS measurements.

다중 유전체에서의 공간전하 분포 측정 및 신호 보정에 대한 연구

다중 유전체에서의 공간전하 분포 측정 및 신호 보정에 대한 연구

Single Electron Precision in the Measurement of Charge Distributions on Electrically Biased Graphene Nanotips Using Electron Holography.

We use off-axis electron holography to measure the electrostatic charge density distributions on graphene-based nanogap devices that have thicknesses of between 1 and 10 monolayers and separations of between 8 and 58 nm with a precision of better than a single unit charge. Our experimental measurements, which are compared with finite element simulations, show that wider graphene tips, which have thicknesses of a single monolayer at their ends, exhibit charge accumulation along their edges. The results are relevant for both fundamental research on graphene electrostatics and applications of graphene nanogaps to single nucleotide detection in DNA sequencing, single molecule electronics, plasmonic antennae, and cold field emission sources.

Automatic Measurement System of the Space Charge Distribution by a Two-Step Deconvolution

The pulsed electro-acoustic method (PEA) is widely used both in laboratory for fundamental research and in industry for high-voltage direct current cable assessment and diagnosis. It is well known that the electrical stress in dielectrics can be influenced by space charges. In this study, we have modified and upgraded the PEA system for better resolution, safety, and measurement of the space charge distributions automatically in a solid dielectric during the application of various DC high voltages. We adapt the PCI extensions for instrumentation system with a DSO/DAQ system for automatic measurements. The system could be used to automatically measure the space charge distribution with higher accuracy under various applied DC voltages.

Direct measurement of surface charge distribution in phase separating supported lipid bilayers

Direct measurement of surface charge distribution in phase separating supported lipid bilayers

Space Charge and Electric Field Analysis on Contaminated XLPE Insulator

<p>Nowadays, XLPE cable has been widely used because it has better resistance than other cables. XLPE insulation has unique features including a high dielectric strength and high insulation resistance. A lot of researches based on hardware and software have been conducted to prove the effectiveness of XLPE cable such as AC and DC applications and Space Charge Distribution measurement under HVDC at High Temperature. This research focused on analysis of space charge and electric field on XLPE cable with effect of non-uniform contamination layer by using Quickfield Software. Non-uniform contaminations have been applied along XLPE cable using Arsenic Tribromide (AsBr3), Boron Bromide (BBr3), Ethylene Dichloride (CH2C1), Formic Acid (CH1O2), Formamide (CH3NO) and Alcohol element. Presence of these contamination elements represent of underground contamination. The size and layer of the contamination were non-uniform type. From the results, it is shown that lower dielectric constant of contamination will affect more on charge of XLPE insulation. As a conclusion, it can be seen lower dielectric constant value of contamination element greatly affecting the performance of XLPE insulation. Furthermore, size of contamination also influences the content of charge in contamination where the bigger the contamination size, the more charge contained in the contamination.</p>

Effects of electric field and temperature on space charge characteristics in double-layered polytetrafluoroethylene films

As the core component of composite insulation for dry-type high-voltage equipment, polytetrafluoroethylene (PTFE) films are subjected to high temperatures and complex electric fields. Therefore, this study explores the effects of electric field and temperature on the space charge characteristics of double-layered PTFE films based on the measurement of space charge distribution in double-layered PTFE films under different DC voltages and temperatures using the pulsed electro-acoustic measurement system. Results show that more charges accumulated in the PTFE sample subjected to a positive electric field during polarization and the space charges dissipated more rapidly during depolarization compared with those subjected to a negative electric field. The existence of a PTFE/PTFE interface increased the density of trap and deepened the trap. The positive charges that accumulated at the PTFE/PTFE interface during polarization gradually held a dominant position with the increase of temperature. Finally, the formation of charge in the PTFE/PTFE interface mainly depended on two factors. When the applied DC voltage was not large, the charge formation was mainly dominated by the Maxwell-Wagner polarization effect. When the voltage increased to a certain threshold, the charge formation was mainly caused by the charge injection and migration characteristics.

Amplified Sensitivity of Nitrogen-Vacancy Spins in Nanodiamonds Using All-Optical Charge Readout.

Nanodiamonds containing nitrogen-vacancy (NV) centers offer a versatile platform for sensing applications spanning from nanomagnetism to in vivo monitoring of cellular processes. In many cases, however, weak optical signals and poor contrast demand long acquisition times that prevent the measurement of environmental dynamics. Here, we demonstrate the ability to perform fast, high-contrast optical measurements of charge distributions in ensembles of NV centers in nanodiamonds and use the technique to improve the spin-readout signal-to-noise ratio through spin-to-charge conversion. A study of 38 nanodiamonds with sizes ranging between 20 and 70 nm, each hosting a small ensemble of NV centers, uncovers complex, multiple time scale dynamics due to radiative and nonradiative ionization and recombination processes. Nonetheless, the NV-containing nanodiamonds universally exhibit charge-dependent photoluminescence contrasts and the potential for enhanced spin readout using spin-to-charge conversion. We use the technique to speed up a T1 relaxometry measurement by a factor of 5.

Direct measurement of surface charge distribution in phase separating supported lipid bilayers.

The local surface charge density of the cell membrane influences regulation and localization of membrane proteins. The local surface charge density could, until recently, not be measured directly under physiological conditions, and it was largely a hypothetical yet very important parameter. Here we use unsaturated lipids of a distinct charge (DOTAP, DOPC, and DOPG) and a neutral fully saturated lipid (DPPC) to create model membranes with phase separating domains of a defined charge. We then apply quantitative surface charge microscopy (QSCM) to investigate the local surface charge density; this is a technique based on a scanning ion conductance microscope (SICM) capable of measuring surface charge density with nanoscale lateral resolution. We are able to clearly distinguish lipid domains from charge and topography in all three model membranes. The measured surface charge densities furthermore reveal that disordered domains formed by charged lipids are in fact not only impure, but also incorporate uncharged saturated lipids. We estimate that at least 30% of disordered domains in DOPG : DPPC and DOTAP : DPPC will be DPPC. These ratios could present a limit for the formation of charged domains in lipid membranes.

Aspects of charge distribution measurement for Cf252 (sf)

Measurements of charge distributions of fragments in the spontaneous fission of $^{252}\mathrm{Cf}$ have been performed using a unique detector setup consisting of a typical grid-ionization chamber coupled with a $\mathrm{\ensuremath{\Delta}}E\ensuremath{-}E$ charged particle telescope. We find that the fragment mass dependency of the kinetic-energy-averaged width of the charge distribution shows a systematically decreasing trend with obvious fluctuations. The variation of the widths of the charge distribution with kinetic energy shows a pan-like shape. This is due to the large number of neutrons emitted at the high excitation energies and cold fragmentation at the low excitation energies. Deviation of the kinetic-energy-averaged most probable charge ${Z}_{p}$ from the unchanged charge distribution (UCD), $\mathrm{\ensuremath{\Delta}}Z$, as a function of the mass number of primary fragments, ${A}^{*}$, changes from negative for mass asymmetric fission to positive near the symmetric fissions. Concerning the kinetic energy dependence of ${Z}_{p}$ given primary mass number ${A}^{*}$, obvious increasing tendencies of ${Z}_{p}$ with increasing kinetic energy are observed.

Charge transport properties of intrinsic layer in diamond vertical pin diode

Diamond is hoped to be utilized in ultimate power electronic devices exhibiting ultra-high blocking voltages. For practical device formation, it is important to characterize the electric properties to precisely simulate carrier transport and to practically design optimum device structures. In this study, we experimentally evaluated the charge transport properties of intrinsic layers in diamond vertical pin diodes using alpha-particle induced charge distribution measurements. The charge collection efficiencies were 98.1 ± 0.6% for a {111} pin diode and 96.9 ± 0.6% for a {100} pin diode, which means that almost all generated charges are collected accordingly equivalent to conventional Silicon pin photodiodes. Mobility-lifetime (μτ) products of holes were (2.2 ± 0.3) × 10−6 cm2/V for {111} and (1.8 ± 0.1) × 10−5 cm2/V for {100} diamond pin diodes.

Contamination effects on charge distribution measurement of high voltage glass insulator string

Abstract It is certain that accumulated charge greatly enhances the local electric field distribution of insulator and may lead to breakdown even under nominal voltage. Although research on charge distribution has gained worldwide attention for the past few decades, yet the study of charge distribution on its surface is still insufficient. Therefore, this paper presents the charge distributions measurement on the surfaces of glass insulators string without grading ring subject to clean and contaminated conditions. The experimental results revealed that the distribution of charge for glass insulator recently removed from service has negative distribution pattern and this is further supported by the simulation work results. Charge injection and extraction occurring at the metal-dielectric interface greatly affects the charge amplitude of the adjacent insulators. This study also revealed that the presence of contamination affect the charge distribution of the insulator located near to ground electrode.