Electron Emission Current Research Articles

Development of Numerical Analysis Method for Cathode Sheath Considering Electron Emission From Cathode in Vacuum Arc

ABSTRACTIt is imperative to develop the simulation of vacuum arcs as a tool to aid electrode design in vacuum circuit breakers. Although the development of electromagnetic thermo‐fluid simulations for vacuum arcs has been reported, most of them do not take cathode sheath phenomena into account and have not been able to reproduce vacuum arc phenomena, especially cathode spots. As the first step, the cathode sheath voltage, cathode surface electric field, and temperature and field (T‐F) electron emission current were analyzed numerically on the basis of the space charge in the cathode sheath. In this study, the cathode sheath was assumed to exist when the charge density induced on the cathode surface is positive, and the temperature and density of vacuum arc plasma and cathode temperature, which are physical quantities obtained by electromagnetic thermo‐fluid simulation, were used as parameters of the analysis. As a result, the cathode sheath voltage, electric field, and electron emission current density can be calculated from the vacuum arc plasma temperature, density, and cathode temperature. Numerical results show that the electron emission current density has a dominant effect on the presence or absence of the cathode sheath.

Evaluate the potential adsorption of graphynes (perfect and doped) for nitrogen mustard gas: A first principles study

Density functional theory (DFT) calculations are used to thoroughly examine the reactivity and electronic sensitivity of pristine and BN-doped graphyne (BNG) toward nitrogen mustard (NM). Graphyne’s electrical conductivity is unaffected by the weak adsorption of NM, which occurs via the Cl atom on the material with an adsorption energy of roughly −3.1 kcal.mol−1. In addition to decreasing graphyne’s reactivity and work function, substituting isoelectronic BN linkages for CC linkages enhances the HOMO-LUMO energy gap (Eg). BNG’s electrical conductivity increases when Eg drops from 2.99 to 1.82 eV due to the adsorption of NM. Additionally, a significant change in BNG’s work function results in a variation in the field electron emission current. Lastly, it is anticipated that the desorption of NM from the BNG surface will take a brief recovery time of roughly 0.05 s at room temperature. It has also been demonstrated that NM concentration affects changes in electrical conductivity. The findings also suggest that BNG could be a promising NM sensor.

Emission characteristics of a forevacuum plasma-cathode source of wide-aperture pulsed electron beam with layer (mesh) stabilization of emission plasma

Research of emission characteristics of a pulsed forevacuum plasma electron source with layer (mesh) stabilization of emission plasma boundary has been carried out. Generation of a pulsed wide-aperture electron beam is provided by DC accelerating voltage (1–10 kV) and pulse-periodic formation of emission plasma by a cathodic arc with current 5–80 A, pulse duration 500–600 μs. Pressure (4–30 Pa) and the type of working gas (N2, O2, Ar, He, Kr) significantly influence on the emission characteristics of the forevacuum plasma electron source. An increase in the gas pressure and the use of gas with larger ionization cross-section provide an increase in the electron emission current. At low pressure (below a certain threshold value, which determined by the type of gas) an increase in the discharge current leads to an increase in the efficiency of electron emission. But at pressures more than the threshold value the emission efficiency decreases as the discharge current increases. The influence of pressure and type of gas on the emission characteristics are caused by the ion flux from the beam plasma which is formed due to ionization of gas by accelerated beam's electrons.

Surface plasmon-mediated enhanced field electron emission based on metasurfaces with a nano-gap driven by LEDs

Vacuum electronic devices have the advantages of no scattering, anti-irradiation, and extreme operating temperatures. With their superiorities, light-assisted field emission can be utilized to drive ultrafast micro-/nano-vacuum electronic devices. However, traditional multiphoton or optical field emission is limited by the access of the lasers with high power and energy. In this Letter, an asymmetric non-semiconductor nanostructure may be applied to reduce cost with a nano-level gas or vacuum channel. We find that the basic LED may be a candidate to enhance the electron emission current by utilizing the multi-stage field enhancement consisting of tip effects and plasmon-based enhancement. By designing a field electron emission device with LEDs in standard atmospheric environment, we realize a 25% increase in field electron emission current at the resonance frequency with the light intensity under W cm−2 and the voltage less than 5 V. By comparing with lasers, simple LEDs are beneficial to increase the scope of applications with low-energy requirements. Meanwhile, the structure paves the way to the application of microelectronic and nano-electronic components in the on-chip electronic devices, such as switches and modulators.

SiO2 etching and surface evolution using combined exposure to CF4/O2 remote plasma and electron beam

Electron-based surface activation of surfaces functionalized by remote plasma appears like a flexible and novel approach to atomic scale etching and deposition. Relative to plasma-based dry etching that uses ion bombardment of a substrate to achieve controlled material removal, electron beam-induced etching (EBIE) is expected to reduce surface damage, including atom displacement, surface roughness, and undesired material removal. One of the issues with EBIE is the limited number of chemical precursors that can be used to functionalize material surfaces. In this work, we demonstrate a new configuration that was designed to leverage flexible surface functionalization using a remote plasma source, and, by combining with electron beam bombardment to remove the chemically reacted surface layer through plasma-assisted electron beam-induced etching, achieve highly controlled etching. This article describes the experimental configuration used for this demonstration that consists of a remote plasma source and an electron flood gun for enabling electron beam-induced etching of SiO2 with Ar/CF4/O2 precursors. We evaluated the parametric dependence of SiO2 etching rate on processing parameters of the flood gun, including electron energy and emission current, and of the remote plasma source, including radiofrequency source power and flow rate of CF4/O2, respectively. Additionally, two prototypical processing cases were demonstrated by temporally combining or separating remote plasma treatment and electron beam irradiation. The results validate the performance of this approach for etching applications, including photomask repair and atomic layer etching of SiO2. Surface characterization results that provide mechanistic insights into these processes are also presented and discussed.

Comparative study on atomically heterogeneous surface with conical arrays of field emitters generated using plasma based low-energy ion beams

A comparative study of the field emission properties of conical arrays of atomically heterogeneous, self-organized, micro–submicro–nanodimensional structures, irradiated at normal incidence by high flux of 2 keV argon (flux=6.47×1015cm−2s−1) and krypton ions (flux=4.81×1015cm−2s−1) on copper substrates, without employing any external seeding, is presented. The variation in surface structural growths with ion beam fluence is investigated using scanning electron, atomic force, and transmission electron microscopy. The exposed surfaces are atomically heterogeneous due to the presence of embedded argon and krypton ions in the interstitial layers (≈nm) as observed from the x-ray photoelectron spectroscopy analysis. Kelvin probe force microscopy is employed to analyze the variation in local work function caused by surface deformities and implantation of inert gaseous ions. The conical arrays are naturally selected field emitter sources, and their field enhancement factor is calculated from the Fowler–Nordheim equations. The argon ion treated substrate at a fluence of 4.85×1018cm−2 gives rise to uniformly distributed structures and has a low turn-on voltage of 2.76 kV with an electron emission current of 0.58 nA. Among the krypton ion irradiated substrates, the sample irradiated at the highest fluence of 5.12×1018cm−2 produces self-organized conical arrays having uniform dimension, orientation, distribution, and even a higher electron emission current of 0.81 nA with a lower turn-on voltage of 2.12 kV. Thus, it may be concluded that krypton ion irradiation provides better generation of naturally selected arrays of field emitters.

Experimental study on the performance characteristics of a miniature microwave discharge cathode

This study experimentally examined several magnetic field topologies for the miniature microwave discharge cathode driven by water, which is indispensable for realizing water ion thrusters. The electron emission currents were measured for various operating conditions; microwave power, mass flow rate, and microwave frequency. The magnetic field topology with the magnetic field lines passing through the orifice hole without intersecting the cathode increased the electron emission current. This result agreed with the prediction derived from the 3D-Particle-in-Cell simulations with Monte Carlo collisions. The measured performance was 11.1 mA electron emission current at 2.0 W microwave forward power and 20μg/s water mass flow rate. On the other hand, the dependency of electron emission current on magnetic field topology became smaller as the mass flow rate or microwave power decreased. Additionally, the performance dependency on mass flow rate was remarkably different by the magnetic field topology. We explained those newly found trends by the difference in electron temperature dependency for the electron transport against the magnetic field lines.

Negative current feedback in the accelerating gap in electron sources with a plasma cathode

Using the example of an electron source with a plasma cathode based on a low-pressure arc discharge with grid stabilization of the cathode/emission plasma boundary and an open anode/beam plasma boundary, a mechanism is described for increasing the electrical strength of a high-voltage accelerating gap by introducing a series negative current feedback (NCF) in the accelerating interval, which makes it possible to level out uncontrolled bursts of the beam current during its pulse. The introduction of NCF is achieved by using a special electrode in the space of the plasma emitter connected through a resistance to the anode of the arc discharge, and the main task of which is to intercept accelerated ions penetrating into the emitter from the high-voltage accelerating gap, due to which the current of electron emission from the arc discharge plasma decreases by a value proportional to the ion current in the accelerating gap. Since most sources and accelerators of electrons with plasma cathodes based on discharges of various types have a similar principle of operation, the use of this method will not only expand the limiting parameters of the generated electron beams, but also increase the stability of the operation of such electron sources, and, accordingly, beam irradiation of various materials and products. Keywords: arc discharge, plasma cathode, electron source, electron beam, ion beam, negative feedback.

Отрицательная обратная связь по току в ускоряющем промежутке в источниках электронов с плазменным катодом

Using the example of an electron source with a plasma cathode based on a low-pressure arc discharge with grid stabilization of the cathode/emission plasma boundary and an open anode/beam plasma boundary, a mechanism is described for increasing the electrical strength of a high-voltage accelerating gap by introducing a series negative current feedback (NCF) in the accelerating interval, which makes it possible to level out uncontrolled bursts of the beam current during its pulse. The introduction of NCF is achieved by using a special electrode in the space of the plasma emitter connected through a resistance to the anode of the arc discharge, and the main task of which is to intercept accelerated ions penetrating into the emitter from the high-voltage accelerating gap, due to which the current of electron emission from the arc discharge plasma decreases by a value proportional to the ion current in the accelerating gap. Since most sources and accelerators of electrons with plasma cathodes based on discharges of various types have a similar principle of operation, the use of this method will not only expand the limiting parameters of the generated electron beams, but also increase the stability of the operation of such electron sources, and, accordingly, beam irradiation of various materials and products.

Влияние рода газа на электрическую прочность ускоряющего промежутка форвакуумного плазменного источника электронов

The electrical strength of the accelerating gap of a fore-vacuum plasma electron source is compared for different working gases: argon, nitrogen, oxygen, and helium. The dependences of the limiting electron emission current, above which breakdown occurs, on the voltage across the accelerating gap are presented. It has been established that the limiting emission currents are determined by the thickness of the emission electrode, the diameter of the holes in it, as well as the gas type and pressure. It has been established that for all gases the limiting emission currents decrease with increasing pressure. The limiting pressures, when exceeded, breakdown occurs, decrease in the series: helium, oxygen, nitrogen, argon. For different experimental conditions, the dependences of the limiting emission currents on the accelerating voltage can be both monotonically growing and containing an extremum.

Incorporating photoemission into the theoretical unification of electron emission and space-charge limited current

Photon emitters are becoming increasingly important due to their ability to generate high brightness, low emittance, and spatiotemporally coherent electron bunches for multiple applications; however, these emitters rarely produce electrons solely due to photoemission. Often, photon emitters are prone to undesired thermionic emission; alternatively, some devices intentionally leverage field and thermionic emission to increase output current. Regardless, attempting to extract higher currents from these devices raises concerns about space-charge buildup. While theories have examined the transitions between many of these mechanisms, none have used a common framework to unify photo-, thermionic, field, and space-charge limited emission simultaneously, typically represented individually by the Fowler–Dubridge (FD), Richardson–Laue–Dushman (RLD), Fowler–Nordheim (FN), and Child–Langmuir (CL) equations, respectively. This paper derives an exact solution unifying these mechanisms and reports conditions where emission bypasses RLD to directly transition from FD to FN based on asymptotically matching the three models at a nexus point. Furthermore, we provide a step-by-step approach for developing nexus phase space plots exhibiting the operating conditions for transitions among FD, RLD, FN, CL, Mott–Gurney for space-charge limited current with collisions, and Ohm's law for an external resistor. We demonstrate the utility of nexus plots for assessing the applicability of the simple well-known theories based on a single mechanism or the necessity to use more complicated solutions combining multiple mechanisms. As such, nexus theory provides a simple framework for guiding theorists in model development, simulation experts in algorithm development and selection, and experimentalists in device design.

Low-energy electron ionization optimization for steroidomics analysis using high-resolution mass spectrometry.

Systematic electron ionization fragmentation studies of steroids have been performed to elucidate and trace their characteristic fragmentation patterns. However, the electron ionization source setting at 70 eV electron energy is much higher than the ionization potential (7-15 eV) of most organic compounds, leading to extensive fragmentation. We present a multifactorial study on optimizing a low-energy electron ionization source to maximize molecular ion formation while minimizing the extent of fragmentation to improve the analytical sensitivity of steroids, especially the more thermolabile ones, while preserving the information that can be extracted from the data. Twenty-seven steroid reference materials, chosen to cover four main classes of urinary steroids, were considered; gas chromatography/quadrupole time-of-flight (GC/qTOF) analyses were carried out using an Agilent Technologies model 8890 gas chromatograph coupled to an Agilent Technologies model 7250 accurate-mass quadrupole time-of-flight (GC/qTOF) instrument. The effects of electron energy, emission current, and source temperature, as well as their potential interactions on steroid fragmentation pathways, have been assessed in full factorial experimental designs. Three parameters were specifically evaluated to improve the chromatographic/spectrometric response of the selected steroids: (i) degree of fragmentation; (ii) relative abundance of the molecular ion; and (iii) peak width. The first two were evaluated by screening designs that highlighted collision energy and source temperature as the most influential factors on the analytical responses of the considered steroids, while emission current always showed a non-significant influence. Then, an optimization design was performed to select the final source setting by searching for the combination of factors that minimize peak tailing. The proposed analytical approach permits a faster selection of optimal experimental conditions for steroidomics analysis using low-energy electron ionization and high-resolution mass spectrometry. The development of these designs of experiments (DoE) in full factorial design (FFD) allowed multiple inputs to be monitored at the same time, highlighting the possible interactions and estimating the effects of a factor in the different levels of the other factors considered.

Effect of a longitudinal magnetic field on the emission characteristics of a forevacuum plasma electron source based on a hollow cathode discharge

The effect of a longitudinal magnetic field on the emission characteristics of a forevacuum plasma electron source based on a discharge with a hollow cathode is studied. It is shown that, starting from a certain threshold value of the induction Bc, the magnetic field leads to a decrease in the plasma concentration on the axis of the cathode cavity. With a decrease in the diameter of the cathode cavity, the threshold value of Bc increases. On the other hand, the longitudinal magnetic field makes it possible to increase the diameter of the emission chan-nel, which contributes to a significant increase in the current of electron emission from the plasma. In this case, the degree of increase in the emission current is determined by the ge-ometry of the cathode cavity and the pressure of the working gas.

Beyond Fowler–Nordheim model: harmonic generation from metallic nano-structures

Metallic structures interacting with electromagnetic fields are known to exhibit properties similar to those found in atoms and molecules, such as multi-photon and tunnel ionization. Developing this similarity beyond the electron emission current, we generalize the well-known Fowler–Nordheim model, and predict a heretofore unrecognized source of nonlinear optical response from nano-structures exposed to illumination with intense optical pulses. We find that the harmonic generation by these structures is non-perturbative in the sense that higher harmonic orders can be almost as strong as the lower orders. At the same time, the predicted spectrum is distinct from the usual high-harmonic generation in that it does not exhibit a sharp cutoff.

Study of the Effects of Thermal Annealing Temperature to Electrochemical Cycling of Mg2+ and Structure of Spinel MgV2O4 Crystals

Spinel vanadium oxides are a promising candidate material for multivalent battery cathodes due to the various possible valence states of V within the spinel framework, which allows for pathways in Mg2+ ion deintercalation [1]. In recent work, Hu et al. experimentally demonstrated that spinel vanadium oxides nanocrystals have a high capacity for Mg2+ electrochemical cycling [2]. While they reported capacities above 200mAh/g at 110 °C, thus outperforming counterparts such as Cr and Mn oxide spinels, it was noted that these capacities are limited by complex defect structures, as suggested by peak pair distances that cannot be explained in the spinel framework in X-ray diffraction measurements.Here, we will utilize atomic-resolution scanning transmission electron microscopy to characterize the structural defects in spinel V2O4 nanocrystals and their possible effect on Mg2+ intercalation. Additionally, we will report the effects of thermal annealing on the structure as a function of temperature and explore the stability of the MgV2O4 nanocrystals. We find that the effects of electron beam exposure can be used as a proxy for damage incurred on the crystals during electrochemical cycling, on the structure of the crystals. The atomic-resolution characterization will be conducted with an aberration-corrected cold field emission JEOL ARM200CF operated at 200kV primary electron energy and emission current of 15μA. The electron probe will be operated at 24mrad convergence semi-angle. High angle annular dark field, low angle annular dark field and annular bright field detectors will be set to the following inner angles: 75 mrad, 30 mrad, 11mrad. X-ray energy dispersive spectroscopy measurements will be conducted using a large solid-angle Oxford XMAX100TLE detector. Additionally, the ARM200CF is equipped with a post-column Gatan Continuum GIF spectrometer providing capabilities for electron energy loss spectroscopy measurements.In this contribution, we will demonstrate that thermal annealing at higher temperatures increases the crystal size of the MgV2O4 crystals while simultaneously decreasing the presence of defect structures. Additionally, we will characterize a variety of defect structures, similar to those shown in Figure 1, present in crystals annealed at lower temperatures using atomic resolved images and electron spectroscopy techniques. [3]Figure 1. LAADF Image showing a grain boundary defect in a spinel MgV2O4 nanocrystal thermally anneal at 400 degrees Celsius.[1] Computer Modeling Investigation of MgV2O4 for Mg-ion Batteries. Navaratnarajah Kuganathan, Konstantinos Davazolglou, Alexander Chroneos; Journal of Applied Physics 2020 127, 035106.[2] High Capacity for Mg2+ Deintercalation in Spinel Vanadium Oxide Nanocrystals. Linhua Hu, Jacob R. Jokisaari, Bob Jin Kwon, Liang Yin, Soojeong Kim, Haesun Park, Saul H. Lapidus, Robert F. Klie, Baris Key,Peter Zapol, Brian J. Ingram, John T. Vaughey, and Jordi Cabana; ACS Energy Letters 2020 5 (8), 2721-2727.[3] This work is solely supported by the Joint Center for Energy Storage Research (JCESR) and Energy Innovation Hub funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences. Figure 1

Effect of space charge on vacuum pre-breakdown voltage and electron emission current

The recent developments in nanosecond pulsed power supplies facilitate the emission of high density electron bursts but their safe operation demands avoiding breakdowns. Using the theoretical and numerical modeling of the electron emission phenomena from a tip (micro-protrusion), the breakdown threshold (pre-breakdown) is analyzed considering it as the highest value of the voltage preserving the system out of the thermo-emission instability regime. However, the space charge that builds up in front of the tip limits the performance of these electron sources by decreasing the local electric field and consequently the thermo-field emission as well as the temperature of the emissive surface. Hence, it is found that the system can safely hold higher voltages (without breakdown) in the presence of dense space charge. In direct current, for a titanium elliptic tip, the highest operation voltage increases by about 15%, whereas for a tungsten hyperbolic tip, it increases by 70%. Remarkably, the emitted current close to the pre-breakdown voltage stays unchanged with or without taking into account the space charge. Surprisingly, when very short pulses (3 ns) are applied to a tungsten hyperbolic tip, the pre-breakdown voltage additionally increases by 30%, and the Coulomb screening, very effective in front of the tip apex, enlarges the electron emission area by 60%, releasing about 1.3 times more electrons compared to vacuum emission (without the space charge). Moreover, the ring effect, experimentally discovered by Dyke and Trolan [Phys. Rev. 89, 799 (1953)] on the radial electron density distribution, can be microscopically observed and understood with your model.

Plasma–liquid interaction during a pulsed vacuum breakdown

The dynamics of phase changes in the material of a copper cathode during the explosion of a microprotrusion on its surface under the action of the explosive electron emission current has been numerically simulated. Numerical data have been obtained that characterize the interaction of the liquid metal and the dense cathode plasma that are formed due to the microprotrusion explosion. It has been shown that, under the action of the pressure exerted by the plasma, the liquid metal is almost completely displaced from the zone of operation of the cathode spot of the vacuum discharge. This leads to the formation of a crater on the cathode surface with microirregularities at its edge. Thus conditions are created for the formation of new microprotrusions, which, when exploding, provide self-sustained and cyclic operation of the vacuum discharge.

Screen-printed Dual-Particle-Containing Multicomponent-Blending Carbon Nanotube Cathode: Enhancement of Electron Emission Characteristics, Current Emission Stability, and Uniformity

The electron emission characteristics, current emission stability, and uniformity of screen-printed carbon nanotube were enhanced by introducing a novel dual-particle-containing multicomponent-blending carbon nanotube cathode via the comprehensive combination of baking in the air and sintering in the inert gas atmosphere. The dual-particle-containing multicomponent-blending carbon nanotube cathode’s design and manufacturing improvements ensured its steeper emission curve variation amplitude, larger maximum emission current, better electron emission current of 806.7 μA was only 2.56 V/μm. When it was increased from 2.78 to 2.91 V/μm, the enhancing current emission amplitude of the proposed cathode was increased by 600.7 μA versus 324.1 μA of the conventional non-blending carbon nanotube cathode. The maximum emission current of the proposed cathode was 3762.5 μA. After the vacant static state of 72 h, the measured emission current had no obvious attenuation, and the fluctuation rate of emission current did not exceed 5%. The backlight unit with dual-particle-containing multicomponent-blending carbon nanotube cathode was sealed, and the obtained emission image had high luminescence brightness and uniformity.

Quantum chemical study on the adsorption of megazol drug on the pristine BC3 nanosheet

ABSTRACT In order to assess the electrical response of the BC3 nanosheets to megazol, computations according to the density functional theory (DFT) have been done. Pristine BC3 is determined to have a notable trend towards the megazol molecules. For the most stable configuration, the adsorption energy is approximately −20.7 kcal/mol. Megazol adsorption makes a noticeable decrease in the gap of HOMO (highest occupied molecular orbital) -LUMO (lowest unoccupied molecular orbital) BC3 nanosheets (from 1.45 to 0.75 V), thereby enhancing the electrical conductivity, which means the BC3 can be a proper choice for megazol detection and electronic sensor applications. Additionally, megazol adsorption has affected the work function of BC3, which remarkably shifts the current of field electron emission from its level, suggesting it for detecting megazol as a function-based sensor. Also, BC3 has the benefit of a short recovery time of approximately 7.72 ms for megazol desorption.

МИНИАТЮРНЫЙ ОРБИТРОННЫЙ ВАКУУММЕТРИЧЕСКИЙ ДАТЧИК С ДВОЙНЫМ АНОДОМ

Miniature (volume~ 6 cm3) ionization vacuum gauge of orbitron type is developed. The anode of orbitron is made as two wolfram wires with 70 μm diameter, located parallel to gauge axis and being at the distance of 0,5 mm from the axis, much smaller than ion collector radii (8 mm). Diameter and length of the collector are 16 mm and 32 mm, accordingly, of the cathode – 70 μm and 9 mm. Potentials of anode and collector are zero, anode potential is 300 V, cathode potential is (5 – 15) V, cathode burning voltage is 1,6 V at the current of 0, 76 A, electron emission current – 5 μA. Binary anode is applied for thermal degasation (gas away) of electrodes. The numerical simulation has shown that electron trajectories have spiral-shuttle form (as at one wire anode). Spiral radius is (1 – 6) mm, step – (4 – 8) mm, rotation and shuttle periods – 6 ns and 30 ns, the number of turns and traveling time – 1500 and 7 μs, path length and energy – 1000 cm and (20 – 200) eV. It was experimentally confirmed that manometer sensitivity is about 1000 Torr– 1, that is 1,5 orders of magnitude more than for PMI-2 ion manometer. The orbitron with binary anode is better than PMI-2 manometer because it has considerably less value of electron current (two orders of magnitude), cathode burning power (5 times) and work volume (3 times).