Electron Beam Current Density Research Articles

Formation of an Au membrane incorporated with carbon atoms under electron beam irradiations

Abstract The Au nanopore can be utilized as optical nano-bio sensor due to its plasmonic effect. Initially, we fabricated the pore membrane inside the focused ion beam drilled Au apertures by using various electron beam irradiations. Depending upon the electron beam current density, the pore closing and opening phenomena of the diffused membrane were examined and characterized by electron probe micro analysis (EPMA), transmission electron microscopy (TEM), and energy –dispersive X-ray analysis (EDAX). No Au atoms were observed right after electron beam irradiations due to the low Au atomic concentrations below the detection limit of TEM. However, after the samples were kept under a laboratory environment for one year, several Au clusters with a size of 5 nm–7 nm were formed on the diffused membrane. This phenomenon can be attributed to Ostwald ripening.

Parametric study of a high current–density EBIS Charge Breeder regarding Two Stream plasma Instability (TSI)

In this paper we report on our results from the design study of an advanced Electron Beam Ion Source (EBIS) based Charge Breeder (ECB). The ECB should fulfill the requirements of the HIE-ISOLDE upgrade, and if possible be adapted for ion injection into TSR@ISOLDE, as well as serve as an early prototype of a future EURISOL ECB. Fulfilling the HIE-ISOLDE/TSR@ISOLDE specifications requires simultaneous increase in electron beam energy, current and current density in order to provide the requested beams with proper charge state, high intensity and with a specified pulse repetition rate.We have carried out a study on the technical requirements of the ECB. The obtained parameters were optimized to comply with technical limitations arising from the electron beam technology and plasma physics in an ECB.

Structural and optical properties of the a-Si:H thin films irradiated by high energetic electron beams

Hydrogenated amorphous silicon (a-Si:H) films deposited on quartz substrate by radio-frequency plasma enhanced chemical vapour deposition were irradiated by an high energetic electron beam source from an electronic gun device. The effects of the high energetic electron beam current density (0.32–0.81 mA/mm2) irradiations on the structural and optical properties of the nc-Si:H thin films have been investigated by atomic force microscopy (AFM), Fourier transform infrared spectroscopy, Raman scattering spectroscopy, X-ray diffraction (XRD) spectroscopy, ultraviolet and visible spectroscopy. The AFM analysis showed increase in the root-mean-square roughness and increase in average grain size. Raman and XRD measurements revealed increasing electron beam current favored enhancement of crystallinity and enlargement of crystallites. The optical band gap of the films is broaden, which can be explained in terms of the reduced hydrogen content and phonon confinement effect. The increasing trend of the B with the variation of electron beam current reveals a more ordered film structure disorder. From the results, it was interesting to found that the optical constants showed a good correlation with the crystallinity within the variation of electron beam current density. The variation of the optical energy gap based on structure disorder and the quantum confinement effect is also discussed.

In-situ synthesis of Ag nanoparticles by electron beam irradiation

Ag nanoparticles were synthesized by electron beam irradiation in the transmission electron microscope chamber at room temperature and the growth mechanism was explored in detail. The sizes of the Ag nanoparticles are controlled by the electron beam current density. Two nanoparticle growth stages were identified. The first growth stage was dominated by the discharging effect, while the second stage was controlled by the heating effect. The nanoparticle synthesis method should be applicable to the synthesis of other metallic nanoparticles.

Surface Charging Considerations for Composite Materials Used in Spacecraft Applications

Graphite composites remain a preferred structural material for modern spacecraft applications despite the growing library of charging data on the surface charging properties of composites and resin. Additional ground test data obtained at a number of relevant temperatures and electron beam current densities extends the collective community knowledge on the charging properties of graphite composites in geostationary earth orbit environments. New data and analyses demonstrate that some common composite materials are susceptible to surface charging at the low current densities (<;100 nA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) expected for lightly shielded or blanketed applications. Scaling results also demonstrate that electrostatic discharge transients occurring on graphite composite surface fail to follow familiar scaling laws.

Transverse acceptance calculation for continuous ion beam injection into the electron beam ion trap charge breeder of the ReA post-accelerator

The ReA post-accelerator at the National Superconducting Cyclotron Laboratory (NSCL) employs an electron beam ion trap (EBIT) as a charge breeder. A Monte-Carlo simulation code was developed to calculate the transverse acceptance phase space of the EBIT for continuously injected ion beams and to determine the capture efficiency in dependence of the transverse beam emittance. For this purpose, the code records the position and time of changes in charge state of injected ions, leading either to capture or loss of ions. To benchmark and validate the code, calculated capture efficiencies were compared with results from a geometrical model and measurements. The results of the code agree with the experimental findings within a few 10%. The code predicts a maximum total capture efficiency of 50% for EBIT parameters readily achievable and an efficiency of up to 80% for an electron beam current density of 1900A/cm2.

Pulsed electron-beam-pumped laser based on AlGaN/InGaN/GaN quantum-well heterostructure

The parameters of pulsed blue-violet ( at ) lasers based on an AlGaN/InGaN/GaN structure with five InGaN quantum wells and transverse electron-beam pumping are studied. At room temperature of the active element, the minimum electron energy was and the minimum threshold electron beam current density was at an electron energy of .

Enhanced relativistic-electron-beam energy loss in warm dense aluminum.

Energy loss in the transport of a beam of relativistic electrons in warm dense aluminum is measured in the regime of ultrahigh electron beam current density over 2×10^{11} A/cm^{2} (time averaged). The samples are heated by shock compression. Comparing to undriven cold solid targets, the roles of the different initial resistivity and of the transient resistivity (upon target heating during electron transport) are directly observable in the experimental data, and are reproduced by a comprehensive set of simulations describing the hydrodynamics of the shock compression and electron beam generation and transport. We measured a 19% increase in electron resistive energy loss in warm dense compared to cold solid samples of identical areal mass.

Biomolecular damage induced by ionizing radiation: the direct and indirect effects of low-energy electrons on DNA.

Many experimental and theoretical advances have recently allowed the study of direct and indirect effects of low-energy electrons (LEEs) on DNA damage. In an effort to explain how LEEs damage the human genome, researchers have focused efforts on LEE interactions with bacterial plasmids, DNA bases, sugar analogs, phosphate groups, and longer DNA moieties. Here, we summarize the current understanding of the fundamental mechanisms involved in LEE-induced damage of DNA and complex biomolecule films. Results obtained by several laboratories on films prepared and analyzed by different methods and irradiated with different electron-beam current densities and fluencies are presented. Despite varied conditions (e.g., film thicknesses and morphologies, intrinsic water content, substrate interactions, and extrinsic atmospheric compositions), comparisons show a striking resemblance in the types of damage produced and their yield functions. The potential of controlling this damage using molecular and nanoparticle targets with high LEE yields in targeted radiation-based cancer therapies is also discussed.

Fast-pulse repetitive frequency emission characteristic of high current carbon nanotubes cathode

With the development of high power microwave technology, the demands for electron beam repetition frequency, current density, response time and emission uniformity are higher and higher. Carbon nanotube (CNt) cathode has been widely investigated, because of its special structure and excellent field emission characteristics. CNt cathode is regarded as a thin film high current cathode, and the interface bonding will affect vacuum performance, stability, lifetime and repeat ability. The direct growth of CNt is a simple and effective means for preparing cathode. When electron energy reaches 1 MeV and the pulse upward gradient attains approximately 60 kV/ns, for CNt cathode, its the emission beam intensity reaches 15 kA and the peak bundle density attains about 1 kA/cm2, the response between beam voltage and current is fast. With the increase of repetition frequency, the emission stability decreases gradually. When the emission power is 15 GW and the emission stability repetitive frequency is 50 Hz, the cathode emission is stable. However with the increase of frequency, the stability becomes weak. When the repetition frequency reaches 100 Hz, voltage and current are almost split into two sections, and the delay time is obviously different. The relation between the voltage and the current meet the exponent law, which is different from the field emission characteristic. After a 1000 shot emission, the morphology of CNt cathode is intact, desorption from the interface of CNt does not happen. So the emission mechanism is flashover plasma emission. Through analyzing the experimental data and considering the plasma expansion effect on diode gap, the plasma speed can be estimated to be about to 3.9 cm/μs.

Nanowire Growth by an Electron‐Beam‐Induced Massive Phase Transformation

Tungsten trioxide nanowires of a high aspect ratio have been synthesized in situ in a TEM under an electron beam of current density 14 A/cm2 due to a massive polymorphic reaction. Sol–gel‐processed cubic phase nanocrystals of tungsten trioxide were seen to rapidly transform to one‐dimensional monoclinic phase configurations, and this reaction was independent of the substrate on which the material was deposited. The mechanism of the self‐catalyzed polymorphic transition and accompanying radical shape change is a typical characteristic of metastable to stable phase transformations in nanostructured polymorphic metal oxides. The findings are important to the controlled electron beam deposition of nanowires for functional applications starting from colloidal precursors.

Determination of the ReA Electron Beam Ion Trap electron beam radius and current density with an X-ray pinhole camera.

The Electron Beam Ion Trap (EBIT) of the National Superconducting Cyclotron Laboratory at Michigan State University is used as a charge booster and injector for the currently commissioned rare isotope re-accelerator facility ReA. This EBIT charge breeder is equipped with a unique superconducting magnet configuration, a combination of a solenoid and a pair of Helmholtz coils, allowing for a direct observation of the ion cloud while maintaining the advantages of a long ion trapping region. The current density of its electron beam is a key factor for efficient capture and fast charge breeding of continuously injected, short-lived isotope beams. It depends on the radius of the magnetically compressed electron beam. This radius is measured by imaging the highly charged ion cloud trapped within the electron beam with a pinhole camera, which is sensitive to X-rays emitted by the ions with photon energies between 2 keV and 10 keV. The 80%-radius of a cylindrical 800 mA electron beam with an energy of 15 keV is determined to be r(80%) = (212 ± 19)μm in a 4 T magnetic field. From this, a current density of j = (454 ± 83)A/cm(2) is derived. These results are in good agreement with electron beam trajectory simulations performed with TriComp and serve as a test for future electron gun design developments.

Low-pressure ETEM Studies of Au assisted MgO Nanorod Growth

Environmental transmission electron microscopy (ETEM) studies MgO nanorod growth from Au catalyst nanoparticles in a controlled gas atmosphere have been performed, in order to elucidate the mobility of Au surface atoms and the configuration of the Au/MgO interface. MgO nanorod growth is driven by the electron beam and found to be strongly dependent on the gaseous environment in the microscope and electron beam current density.

Microbeam methods for the analysis of glass in fine-grained tephra deposits: a SMART perspective on current and future trends

Abstract Correlation of tephra deposits frequently relies on the analysis of glass shards separated from their host. Small shards from distal deposits (marine-, ice- or lake-cores, peat bogs) are difficult to analyse. Here current methods for glass shard analysis from (particularly) marine tephra deposits are reviewed. These methods apply equally to other distal deposits, where linking repositories of climatic information is central to many research programmes. Electron probe microanalysis is used widely to determine the major element compositions of volcanic glass. However, electron beam irradiation causes permanent damage to glass, especially hydrated or silica- and alkali-rich compositions. Recent developments have shown that reliable data is obtained with beam diameters &gt;3 µm on basaltic or moderately hydrated rhyolitic glass, provided low electron beam current densities are used. For robust correlation of tephra deposits from different environments, it is recommended that analytical data are normalized to an anhydrous basis. Glass trace element analysis is commonly performed by laser ablation inductively coupled plasma mass spectrometry, which determines approx. 30 elements at &lt;1 ppm from ablation craters 10 µm diameter, and although element fractionation occurs, it can be corrected. Recent developments in both methods should facilitate analysis of smaller, more distal material, expanding the geographical range over which reliable tephra correlations can be achieved.

A high-current electron gun for the electron beam ion trap at the National Superconducting Cyclotron Laboratory

The Electron Beam Ion Trap (EBIT) in NSCL's reaccelerator ReA uses continuous ion injection and accumulation. In order to maximize capture efficiency and minimize breeding time into high charge states, the EBIT requires a high-current/high current-density electron beam. A new electron gun insert based on a concave Ba-dispenser cathode has been designed and built to increase the current transmitted through the EBIT's superconducting magnet. With the new insert, stable EBIT operating conditions with 0.8 A of electron beam have been established. The design of the electron gun is presented together with calculated and measured perveance data. In order to assess the experimental compression of the electron beam, a pinhole CCD camera has been set up to measure the electron beam radius. The camera observes X-rays emitted from highly charged ions, excited by the electron beam. Initial tests with this camera setup will be presented. They indicate that a current density of 640 A/cm(2) has been reached when the EBIT magnet was operated at 4 T.

Commissioning results of the ReA EBIT charge breeder at the NSCL: First reacceleration of stable-isotope beams

ReA is a reaccelerator of rare-isotope beams at the National Superconducting Cyclotron Laboratory (NSCL). The rare isotopes are produced by fast projectile fragmentation. After production, they are separated in-flight and thermalized in a He gas “catcher” cell before being sent to ReA for reacceleration to a few MeV/u. One of its main components is an electron-beam ion trap (EBIT) employed to convert injected singly charged ions to highly charged ions prior to injection into linear-accelerator structures. The ReA EBIT features a high-current electron gun, a long trap structure, and a two-field superconducting magnet to provide both the high electron-beam current density needed for fast charge breeding and high capture probability of injected beams. This paper presents recent commissioning results. In particular, 39K+ ions have been injected, charge bred to 39K16+ and extracted for reacceleration up to 60MeV. First charge-breeding results of beams injected from a commissioning Rb ion source in the NSCL’s beam “stopping” vault are also presented.

Effect of cathode materials on the generation of runaway electron beams and X-rays in atmospheric pressure air

AbstractIn this work, experiments were performed to study the effect of cathode materials on the amplitude of the super-short avalanche electron beam (SAEB) current and X-ray density during discharges in atmospheric-pressure air. In the experiments, discharges were generated by three nanosecond-pulse generators in air gaps between a plane anode and a tubular cathode made of different metals. The output pulse of the three generators had a rise time of 0.3, 1, 15 ns, and a full width at half maximum of 1, 2, 30–40 ns, respectively. For the generators with pulse rise-time of 0.3 and 1 ns, the cathodes used in these experiments were made of stainless steel, permalloy, titanium, niobium, copper, brass, and aluminum. For the generator with pulse rise-time of 15 ns, the cathodes were made of stainless steel, titanium, copper, and aluminum. When the rise time of the applied pulse is 0.3 ns, our experimental results show that the amplitude of the voltage across the gap depends on the cathode material and reaches its maximum value when a stainless steel cathode is used. It is also observed that, under such situation, the maximum amplitudes of the SAEB current occur at maximum voltages across the gap when all other factors are equal. Furthermore, the amplitude of the SAEB current hereof is found to depend not only on the material of the sharp edge of the tubular cathode, but also on the material of the side surface of the tubular cathode. When the rise time of the applied pulse is 1 ns, the experimental results show that the average number of electrons in SAEB is also affected by the cathode materials. In addition, in the case that the rise time of the voltage pulse is 15 ns and the gap spacing is 8 cm, the experimental results show that the cathode material has no effect on the voltage amplitude across the gap and the X-ray density. The increase of the pulse repetition frequency from 250 to 500 Hz under such condition can lead to a three-fold increase in X-ray density in a repetitive pulsed mode.

An Analytical Method of Time Character of Electron Beam Current Density on Transmission Electron Microscope Imaging

An analytical method of time character of electron beam current density is required for transmission electron microscopy (TEM) imaging research. By studying the imaging principle of TEM, the relational expression between current density on fluorescent screen and exposure time is deduced. The actual data of numerical relation between current density and exposure time are gained by the exposure experimentation with the master sample on the TEM test equipment. Furthermore, the parameter value in expression is computed by linear fit using the least squares method, and then the concrete relational expression between current density and exposure time about the TEM test equipment is obtained. As a result, using the concrete relational expression on the TEM test equipment, the automatic exposure experimentation on some samples is completed on the different operating mode, and the relatively clear-cut TEM images are formed. The experimentation results indicate that the automatic exposure method is correct and parameter calibration is valid.

Enhanced coherent terahertz Smith-Purcell superradiation excited by two electron-beams

This paper presents the studies on the enhanced coherent THz Smith-Purcell superradiation excited by two pre-bunched electron beams that pass through the 1-D sub-wavelength holes array. The Smith-Purcell superradiation has been clearly observed. The radiation emitting out from the system has the radiation angle matching the 2nd harmonic frequency component of the pre-bunched electron beams. The results show that the two electron beams can be coupled with each other through the holes array so that the intensity of the radiated field has been enhanced about twice higher than that excited by one electron beam. Consequently superradiation at the frequency of 0.62 THz can be generated with 20A/cm(2) current density of electron beam based on above mechanism. The advantages of low injection current density and 2nd harmonic radiation promise the potential applications in the development of electron-beam driven THz sources.

Influence of total beam current on HRTEM image resolution in differentially pumped ETEM with nitrogen gas

Environmental transmission electron microscopy (ETEM) enables the study of catalytic and other reaction processes as they occur with Angstrom-level resolution. The microscope used is a dedicated ETEM (Titan ETEM, FEI Company) with a differential pumping vacuum system and apertures, allowing aberration corrected high-resolution transmission electron microscopy (HRTEM) imaging to be performed with gas pressures up to 20 mbar in the sample area and with significant advantages over membrane-type E-cell holders. The effect on image resolution of varying the nitrogen gas pressure, electron beam current density and total beam current were measured using information limit (Young's fringes) on a standard cross grating sample and from silicon crystal lattice imaging. As expected, increasing gas pressure causes a decrease in HRTEM image resolution. However, the total electron beam current also causes big changes in the image resolution (lower beam current giving better resolution), whereas varying the beam current density has almost no effect on resolution, a result that has not been reported previously. This behavior is seen even with zero-loss filtered imaging, which we believe shows that the drop in resolution is caused by elastic scattering at gas ions created by the incident electron beam. Suitable conditions for acquiring high resolution images in a gas environment are discussed. Lattice images at nitrogen pressures up to 16 mbar are shown, with 0.12 nm information transfer at 4 mbar.