Beam Current Increases Research Articles

Transparent Conductive p-Type Cuprous Oxide Films in Vis-NIR Region Prepared by Ion-Beam Assisted DC Reactive Sputtering

Cu2O thin film has been widely studied due to its intrinsic p-type conductivity. It can be used as p-type transparent conductive electrode or hole transport layer in various potential applications. However, its intrinsic p-type conductivity is very limited, which needs to be optimized by introducing acceptor defects. In this work, the electrical properties of the Cu2O films was improved through introducing interstitial oxygen in the films those were deposited via direct current sputtering assisted by oxygen ion beam. The results show that with oxygen ion beam current increase, the carrier concentration effectively improves. However, with more interstitial oxygen introduced, the film’s crystallinity significantly reduces, as well as the carrier mobility decreases. Meanwhile, all of the Cu2O films present moderate transmittance in the visible region (400–800 nm), but ideal transmittance in the near infrared (NIR) light region (800–2500 nm). When compared with the strong reflection of the n-type transparent conductive film to the near infrared light, the Cu2O film is transparent conductive in NIR region, which expands its application in the fabrication of NIR electrical devices.

PIC Simulation of Pseudospark Discharge-Based Plasma Cathode Electron Source for the Generation of High Current Density and Energetic Electron Beam

A plasma cathode electron (PCE) source using single-gap to multigap pseudospark discharge (PD) for the generation of high density and energetic electron beams has been proposed based on our study with the help of OOPIC PRO simulation code. The simulation model comprises the successive high voltage breakdown and plasma discharge processes for single-gap to multigap PD-PCE sources. A combined analysis of a single gap to multigap PD-PCE source with the operating gas pressures 20–60 Pa, the applied voltages 20–35 kV, and the electrode aperture sizes 2–6 mm for the generation of pulsed electron beams suitable for potential and growing applications in extreme ultraviolet (EUV)/Soft X-ray, microwave, and surface modification is presented. Trigger electrons are used to form the controlled and efficient plasma inside the hollow cathode cavity. The generated high density ( $\sim \!\!{2.8} \times {10}^{{{5}}}$ A/cm2) and up to 32-kV electron beams are governed by the penetrated dynamic equipotential lines. The electron beam current increases with the increase of gas pressure and the number of gaps and decreases for the increase in the diameter of the electrode apertures of the PD-PCE source. The investigation has helped to generate the required electron beam by optimizing the operating and geometrical parameters of the PD-PCE source.

Influences of Oxygen Ion Beam on the Properties of Magnesium Fluoride Thin Film Deposited Using Electron Beam Evaporation Deposition

Magnesium fluoride (MgF2) materials are commonly used for near/medium infrared anti-reflection optical coatings due to their low refractive index and wide-range transparency. Ion assistant deposition is an important technique to increase the density of MgF2 and reduce absorption around 2.94 µm caused by high porosity and moisture adsorption. However, the excessive energy of Argon ion will induce a color center and; therefore, lead to UV/Visible absorption. In this paper, oxygen ion was introduced to reduce the color center effect in MgF2 thin film deposited using electron beam evaporation with ion assistant. The films were deposited on Bk7 and single crystal silicon substrates under various oxygen ion beam currents. The microstructure, optical constant, film density, stress, and adhesion are investigated, including the absorption properties at the infrared hydroxyl (–OH) vibration peak. The results show that as the oxygen ion beam current increases, the absorption value at the position of the infrared OH vibration, defects, and stress of the film decrease, while the refractive index increases. However, MgF2 has poor adhesion using oxygen ion-assisted deposition. Thin MgF2 film without ion beam assistant was used as adhesive layer, high density, and low absorption MgF2 film with good adhesion was obtained.

A new method of low-temperature cementation of stainless steel by decomposition of C2H2 in low-energy electron beam generated plasma

The method of low-temperature (400–500°C) cementation of AISI430 stainless steel by decomposition of acetylene in a wide (100 cm2) low-energy (200–300 eV) electron beam generated plasma in an Ar+C2H2 gas mixture was investigated. The composition of a beam Ar+C2H2-plasma is investigated and it is shown that the degree of decomposition of acetylene varies with the current and energy of the electron beam. It is shown that the magnitude of the flow of acetylene significantly affects the formation rate and hardness of the hardened layer. From the obtained results it can be seen that at fixed values of argon pressure ( ~ 0.8 mTorr), beam current (3.5 A), bias voltage (–120 V), sample temperature (500°C) and exposure time (3 h) increase in QC2H2 from 1 to 4–5 cm3·min−1 leads to an increase in the thickness and microhardness of the hardened layer. With a further increase in QC2H2, an abrupt decrease in the rate of formation of the hard layer occurs.

Investigation on Microstructure, Hardness and Wear Resistance of Electron Beam Wire-Feeding Deposited Inconel 718 Alloy Coatings

The Inconel 718 (IN718) alloy coatings were successfully fabricated using electron beam wire-feeding deposition technology. The macrostructure, microstructure and elemental analysis of the deposited coatings were characterized by OM, SEM and EDS. Moreover, the hardness and wear resistance were also investigated experimentally. The results showed that the cross section of the deposited coatings can be divided into three different regions: clad zone (CZ), fusion zone (FZ) and heat affected zone. Equiaxed dendrites appeared in the CZ while columnar dendrites occurred in the FZ, and discrete fine Laves phase particles were formed under low beam current while continuous coarse Laves phase particles were found under high beam current. The EDS results showed that the degree of Nb segregation in FZ is higher than that in CZ. More importantly, the microstructure coarsened and the degree of Nb segregation increased with the increase of beam current. The deposited coating under the lowest beam current (10 mA) has the highest hardness (263 HV0.2) and the minimum specific wear rate (3.95391 × 10−15 m3/Nm), which is corresponding to the fine microstructure, discrete Laves phase particles and low degree of Nb segregation under low beam current.

Effect of the Beam Current during the Electron-Beam Melting of Titanium Alloy Ti–6Al–4V on the Structural Features and Phase Transitions in Gas-Phase Hydrogenation

The structure of the titanium alloy Ti–6Al–4V manufactured by electron-beam melting is shown to be represented by initial β-phase grains more than 40 μm in size; the internal volume of the grains is filled with α-phase precipitates in the form of plates. The average size of the α plates is 1.6, 2, and 5 μm at beam currents of 2, 2.5, and 3 mA, respectively. In situ X-ray diffractometry using synchrotron radiation shows that the phase transitions in the titanium alloy are divided into three main stages during hydrogenation to a concentration of 0.6 wt % at a temperature of 650°C and a pressure of 1 atm. An increase in the beam current from 2 to 3 mA does not significantly affect the phase composition of the alloy. During hydrogenation, the growth rate of the volume concentration of the β phase is lower at a higher beam current. This indicates a decrease in the rate of hydrogen absorption with increasing beam current, which is associated with an increase in the size of α plates.

Adjustable pulse width and high repetition frequency electron beam extraction from vacuum arc plasma

We investigate the generation of high repetition frequency electron beam from vacuum arc plasma source, which consists of Cu cathode and hollow anode. The frequency and pulse width of the extraction pulse power supply based on MOSFET can be adjusted continuously. A self-trigger circuit is designed to immediately reignite DC arc after its extinguishment and guarantee the discharge duration time and stability. The experimental results show that the repletion frequency and pulse width of the electron beam are controlled by the extraction pulse voltage parameters. With a certain discharge current, the beam current increases with the increasing extraction voltage and shows a saturation limit up to 1A. However, the extraction voltage with too high pulse frequency or pulse width is not conducive to the stability of the beam current.

Emittance compensation schemes for a superconducting rf injector

Contemporary particle injector technologies provide different advantages depending on the chosen design. In the case of copper rf injectors these is primarily the high accelerating field, enabling the generation of high charge bunches with very low emittance. However, the cost of that is a comparably low repetition rate. DC guns, on the other hand, can provide higher repetition rates and consequently increased beam currents at lower beam quality, i.e., increased emittance. The concept of a superconducting rf injector offers the opportunity to combine the advantages of both these concepts. However, it demands special concepts for emittance compensation, as the common approach with overlapping magnetic fields during the rf acceleration interferes with the limitations of superconductivity. The ELBE SRF Gun project is one of the most advanced in this field. Gun II, the second SRF injector at the Electron Linear accelerator with high Brilliance and low Emittance (ELBE), introduces new features for emittance compensation which were studied in detail over the last years. One of these methods is the integration of a superconducting solenoid into the cryostat. Another method uses rf focusing by retracting the photocathode's tip from the last cell of the resonator. This paper discusses both of these schemes by briefly outlining their setups, discussing results of numerical simulations of their impact, and presenting results of initial experimental beam measurements with Gun II.

Effect of the continuous electron beam process treatment in the surface modification of T10 steel

Surface modification is an important component of improving mechanical properties in mold manufacturing. In the present work, the microstructure and properties of modification layer and the influence of the continuous electron beam process parameters on modification layer of T10 steel are investigated by using a scanning electron beam. Morphology of cross-section presents a stack shape after treatment. Meanwhile the microstructure of cross-section consists of three parts: remelted layer, heat affected zone and substrate. Microstructure of remelted layer consists of acicular and lath martensite and the grains are uniform and tiny after treatment. Surface microhardness increases before decreasing, and the microhardness of sample surface increases to 839HV from 252HV, the statistics after treatment is three times as much as that before treatment. According to the influence of continuous electron beam process on modification layer, surface microhardness increases nonlinear with the increasing beam current, surface roughness increases after decreasing with the increasing beam current, while wear resistance increases before decreasing with the increasing beam current.

Investigation of Electron Beam Generation in Pseudospark Discharge-Based Plasma Cathode Electron Source

In this paper, an investigation has been carried out for the generation of electron beam in the pseudospark discharge-based plasma cathode electron (PD-PCE) source for a wide range of geometrical and operating parameters, such as cathode aperture, gas pressure, and seed electron energy, using 2-D kinetic plasma simulation code. It has been observed that the peak electron beam current’s time to appear at the anode surface decreases with an increase in the cathode aperture size, gas pressure, and injected seed electron energy. Investigation of the peak electron beam current and its time to appear at the anode is presented with reference to the variation of cathode aperture and gas pressure. It has been found that the generated electron beam current increases with increase in gas pressure while decreases with increase in the cathode aperture. The potential profile is also presented which is responsible for confinement of the plasma inside the hollow cathode (HC) cavity. The simulation has been performed for the required aperture size 2–10 mm, argon gas pressure 20–80 Pa, and seed electron energy 1–4 kV. The gas pressure, cathode aperture, and seed electron energy strongly influence the growth of plasma inside the HC cavity and also the generation of corresponding energetic electron beam. As a result, electron beams of different current amplitudes, sizes, and energies can be realized by proper control of the gas pressure, cathode aperture size, and seed electron energy of PD-PCE source for its use in extreme ultraviolet/X-ray and microwave applications.

How should a fixed budget of dwell time be spent in scanning electron microscopy to optimize image quality?

In scanning electron microscopy, the achievable image quality is often limited by a maximum feasible acquisition time per dataset. Particularly with regard to three-dimensional or large field-of-view imaging, a compromise must be found between a high amount of shot noise, which leads to a low signal-to-noise ratio, and excessive acquisition times. Assuming a fixed acquisition time per frame, we compared three different strategies for algorithm-assisted image acquisition in scanning electron microscopy. We evaluated (1) raster scanning with a reduced dwell time per pixel followed by a state-of-the-art Denoising algorithm, (2) raster scanning with a decreased resolution in conjunction with a state-of-the-art Super Resolution algorithm, and (3) a sparse scanning approach where a fixed percentage of pixels is visited by the beam in combination with state-of-the-art inpainting algorithms. Additionally, we considered increased beam currents for each of the strategies. The experiments showed that sparse scanning using an appropriate reconstruction technique was superior to the other strategies.

Morphologies and optical and electrical properties of InGaN/GaN micro-square array light-emitting diode chips.

InGaN/GaN micro-square array light-emitting diode (LED) chips (micro-chips) have been prepared via the focused ion beam (FIB) etching technique, which can not only reduce ohmic contact degradation but also control the aspect ratio precisely in three-dimensional (3D) structure LED (3D-LED) device fabrication. The effects of FIB beam current and micro-square array depth on morphologies and optical and electrical properties of the micro-chips have been studied. Our results show that sidewall surface morphology and optical and electrical properties of the micro-chips degrade with increased beam current. After potassium hydroxide etching with different times, an optimal current-voltage and luminescence performance can be obtained. Combining the results of cathodoluminescence mappings and light output-current characteristics, the light extraction efficiency of the micro-chips is reduced as FIB etch depth increases. The mechanisms of micro-square depth on light extraction have been revealed by 3D finite difference time domain.

P-type conductive NiOx: Cu thin films with high carrier mobility deposited by ion beam assisted deposition

Transparent conductive NiO thin films with 18at% Cu dopant were fabricated by ion beam assisted deposition (IBAD). Their structural and optoelectronic properties were compared with undoped NiO films and NiO films doped with 12at% Cu, and also compared with NiO:Cu (18at%) films deposited by RF sputtering as reported in our previous work. The results show that the crystallinity of NiO thin films deposited through IBAD technology is much better than that of the films deposited by RF sputtering. Thanks to this reason, the highest carrier mobility above 45cm2V−1s−1 for NiO:Cu (18at%) film can be realized here. Meanwhile, the films’ resistivity remains an acceptable value, varying from 2.05 to 0.064Ωcm with oxygen ion beam current changing from 0.2 to 0.8A. This feature is imperative for p-type transparent conductive oxides (TCOs) applied in various domains. In addition, with oxygen ion beam current increase, the increase of the Ni3+/Ni2+ ratio leads to more Ni2+ vacancies be introduced into NiO films, which is beneficial to generate holes and improve carrier concentration. In this work, the optimal carrier mobility of NiO film doped with 18at% Cu is obtained when the oxygen ion beam current is 0.2A. Its carrier concentration and electrical resistivity are 7.26 ×1016cm−3 and 2.05Ωcm, respectively.

Cumulation of High-Current Electron Beams: Theory and Experiment

High-power electron beam cumulation in a relativistic vacuum diode with a ring-type cathode is considered. The term “electron beam cumulation” here means electron beam self-focusing accompanied with multifold beam current density increase on the beam axis compared to the average current density in the cathode-anode gap. Space-charge repulsion of electrons emitted by the explosive-emission plasma on the inner edge of the cathode is shown to be the origin of this cumulation mechanism. Current density in the vicinity of beam axis is evaluated for different cathode inner diameter values both numerically and experimentally. Cathode with eccentric apertures of different diameters is studied experimentally.

Optical transparency radial distribution of ion thruster

The optical system is one of the main components of an ion thruster, which consists of electrically biased multi-aperture grids. The grid design is critical to the ion thruster operation since its transparency has an important influence on the thruster efficiency and thrust. To further optimize the optical system performance and evaluate effectively the efficiency of ion thruster, the optical transparency radial distribution of ion thruster is analyzed and discussed in experiment and simulation. The process of beam extraction is simulated by the particleincell-Monte Carlo collision (PIC-MCC) method, and the movement of the ions is investigated by the PIC method while the collisions of particles are handled by the MCC method. Then the interdependency among the transparency of screen grid, the accelerator grid, optics system and the number of ion extracted is analyzed. Taking into account the distribution of ion density at the exit of discharge chamber, the radial distribution of the screen grid transparency, accelerator grid transparency and optical system transparency are acquired. An experiment is performed to verify the simulation based derivation, indicating the good agreement between experimental and simulation results. The results show that the radial distribution of screen grid transparency increases gradually along the radial direction and has a good central axial symmetry, and its minimum value is located in the center of the thruster while the maximum value is near the margin region of screen gird. The radial distribution of accelerator grid transparency is opposite to that of the screen grid transparency, which decreases along the radial direction, and its maximum value is located at the axis of the thruster. The radial distribution of optical system transparency is the same as that of the screen grid transparency. And its minimum value is in the center of optics system, which indicates that the effect of accelerator grid transparency on the optical system transparency is little. In addition, the study also finds that the total optical transparency of ion thruster decreases slowly as the beam current increases. This work will provide a lot of support for the optimal design of ion thruster optics system.

Spot-welding solid targets for high current cyclotron irradiation

Zirconium-89 finds broad application for use in positron emission tomography. Its cyclotron production has been limited by the heat transfer from yttrium targets at high beam currents. A spot welding technique allows a three-fold increase in beam current, without affecting 89Zr quality. An yttrium foil, welded to a jet-cooled tantalum support base accommodates a 50µA proton beam degraded to 14MeV. The resulting activity yield of 48±4 MBq/(μA∙hr) now extends the outreach of 89Zr for a broader distribution.

Research on the effect of cathode plasma expansion on x-band relativistic backward wave oscillator using moving-boundary conformal PIC method

The cathode plasma expansion has been widely investigated and is recognized as impedance collapse in a relativistic backward wave oscillator (RBWO). However, the process of formation and expansion of cathode plasma is very complicated, and the thickness of plasma is only several millimeters, so the simulation of cathode plasma requires high temporal and spatial resolutions. Only the scaled-down diode model and the thin gas layer model are considered in the previous hybrid simulation, and there are few numerical studies on the effect of cathode plasma expansion on the RBWO. In this paper, the moving-boundary conformal particle-in-cell method is proposed; the cathode plasma front is treated in this novel method as the actual cathode surface, and the explosive electron emission boundary moves as the expansion of cathode plasma. Moreover, in order to accurately simulate the electromagnetic field near the cathode surface, the conformal finite-difference time-domain method based on the enlarged cell technique is adopted. The numerical simulation indicates that the diode voltage decreases and the beam current increases as cathode plasma expands; when the cathode plasma velocity is 10 cm/μs, the pulse duration of the generated microwave decreases from 30 ns to 10 ns, the working frequency decreases from 9.83 GHz to 9.64 GHz, and the output power decreases 30% in the course of cathode plasma expansion.

Influence of the electrode gap separation on the pseudospark-sourced electron beam generation

Pseudospark-sourced electron beam is a self-focused intense electron beam which can propagate without any external focusing magnetic field. This electron beam can drive a beam-wave interaction directly or after being post-accelerated. It is especially suitable for terahertz radiation generation due to the ability of a pseudospark discharge to produce small size in the micron range and very high current density and bright electron beams. In this paper, a single-gap pseudospark discharge chamber has been built and tested with several electrode gap separations to explore the dependence of the pseudospark-sourced electron beam current on the discharge voltage and the electrode gap separation. Experimental results show that the beam pulses have similar pulse width and delay time from the distinct drop of the applied voltage for smaller electrode gap separations but longer delay time for the largest gap separation used in the experiment. It has been found that the electron beam only starts to occur when the charging voltage is above a certain value, which is defined as the starting voltage of the electron beam. The starting voltage is different for different electrode gap separations and decreases with increasing electrode gap separation in our pseudospark discharge configuration. The electron beam current increases with the increasing discharge voltage following two tendencies. Under the same discharge voltage, the configuration with the larger electrode gap separation will generate higher electron beam current. When the discharge voltage is higher than 10 kV, the beam current generated at the electrode gap separation of 17.0 mm, is much higher than that generated at smaller gap separations. The ionization of the neutral gas in the main gap is inferred to contribute more to the current increase with increasing electrode gap separation.

Beam Interactions With Surface Waves and Higher Order Modes in Oversized G-band Slow-Wave Structure

Beam interactions with surface waves and higher order modes in oversized $G$ -band slow-wave structures (SWSs) are studied in a coaxial SWS. The coaxial SWS reduces the number of higher order mode and eases the mode competition problem. The SWS is excited by an annular electron beam. The slow cyclotron (SC) interaction as well as the Cherenkov interaction occurs due to 3-D beam perturbations of the electron beam. Growth rates for the surface waves are larger than those for the higher order modes and increase with increasing beam current. The SC interaction merges with the Cherenkov interaction for a sufficiently high beam current and a relatively low magnetic field. And the merged growth rate also increases with the beam current.

Feasibility study on high current ion beam extraction from anode spot plasma for large area ion implantation

In this paper, we have investigated the feasibility of the high current beam extraction from anode spot plasma as an ion source for large area ion implantation. Experiments have been carried out with the ambient plasma produced by inductive coupling with radio-frequency (RF) power of 200 W at the frequency of 13.56 MHz. Anode spot plasmas are generated near the extraction hole of 2 mm in diameter at the center of a bias electrode whose area exposed to the ambient plasma can be changed. It is found that the maximum ion beam current is extracted at the optimum operating pressure at which the area of bias electrode exposed to ambient plasma is fully covered with the anode spot plasma whose size is dominantly determined by the operating pressure for given gas species. It is also observed that the extracted ion beam current increases nonlinearly with the bias power due to the changes in size and shape of the anode spot plasma. With the well-established anode spot plasma operating at the optimum gas pressure, we have successfully extracted high current ion beam of 6.4 mA (204 mA/cm2) at the bias power of 22 W (∼10% of RF power), which is 43 times larger than that extracted from the plasma without anode spot. Based on the experimental results, criteria for electrode design and operating pressure for ion beam extraction from larger extraction aperture are suggested. In addition, the stability of anode spot plasma in the presence of ion beam extraction through an extraction hole is discussed in terms of the particle balance model.