High Voltage Electron Beam Research Articles

생물시료의 3D Tomogram 정밀도 개선을 위한 Band-pass Filtering 활용

Electron tomography (ET) of biological specimens is performed from a series of images obtained over a range of tilt angles in a transmission electron microscope. When using the high voltage electron microscope (HVEM), various noises appear in EM images acquired from thick sections by high voltage electron beam. In order to obtain an adequate result in electron tomograms that allow visualization of rather complex and mega-cellular struc- ture such as brain tissue, it is necessary to remove the noise in each original tilt images of thick section. Using band-pass filtering of original tilt images, the filtered images are obtained and used to assemble a reconstructed tomogram. The qualified 3D tomogram from filtered images results in a considerable reduction of the noises compared to conventional tomogram. In conclusion, this study suggests that band-pass filtering is effective to improve the brightness and intensity of HVEM produced tomograms acquired from micron-thick sections of biological specimens. (류근용, 김미 정, 최기주, 제아름, 김수진, 이철현, 정현석, 박종원, 권희석: 생물 시료의 3D Tomogram 정밀도 개선을 위한 Band-pass Filtering 활용)

Direct observation of the inner structure of unstained atmospheric cells by low-energy electrons

Imaging at nanometre-scale resolution is indispensable for many scientific fields, such as biology, physics, chemistry, materials science and nanotechnology. Electron microscopy is an important technique to produce high-resolution images of biological samples. Inner structure inspection of cell samples of a few micrometre thickness is enabled using a high-voltage electron beam (EB) of around 1000 kV. However, large and complex equipment is required for such systems. Therefore, a more convenient and simple measurement system is desired. Here, we show clear observations of the inner structure of unstained atmospheric cells using a low-voltage EB of less than 10 kV. Experiments suggest that whole cell imaging by a low-voltage EB is enabled by the transmission electrons (TEs), and TEs are of very low energy of less than 20 eV. Therefore, the damage to the biological samples is very low. Our microscope system can easily be applied for diverse samples, such as cells, bacteria, viruses and other organic samples.

Development of Methods to Observe a Living Cell and Macromolecules in Aqueous Solution with Scanning Electron Microscope at Nanometer Resolution

In electron microscopy, transparency of specimens against a beam of electrons in TEM or intensity of secondary electrons and so on induced by an incident electron beam in SEM is translated into contrast. Any material surrounding a specimen, which prevents electron beam passing or detection of secondary electrons, obstructs to create an image. Hence, electron microscopy intrinsically requires high voltage electron beam irradiation of specimens and high vacuum under 10-4 Pa in the cell for specimens. Water in samples must be replaced with some resins or completely dried up. These conditions make it difficult to observe wet or living samples like enzymes retaining catalytic activities or living cells in aqueous solution. To image wet and living samples using electron microscopy at nanometer resolution, we are developing a new wet cell for SEM whereby living cells and enzymes can be maintained in aqueous solution. A carbon thin layer with thickness of 20 nm was made by vacuum evaporation. We applied it as a diaphragm withstanding a pressure gap for separating a specimen in solution at atmospheric pressure from high vacuum environment. Cells and enzymes were placed on its surface of the atmospheric side. They were imaged using SEM. The EM photographs show detailed structures of the cell membrane and the enzymes.

The Performance Optimization Design of High Frequency and High Voltage Transformer of Electronic Beam Welder

High-frequency digital inverter power supply has the advantages of small, no noise, high efficiency, small ripp- le, and perfect protection, therefore, is gradually replacing the traditional electron beam welder which uses the 400Hz frequency generator. However, with more high frequency of the power supply, the design of the transformer used by the high-frequency high-voltage electron beam welding becomes difficult. Therefore, this paper put forward a diversified transformer mode and a voltage doubling rectifier circuit, which were used to reduce the transformer turns ratio, thus reducing the topology of the transformer distribution para- meters. Accordingly, a special high-frequency high-voltage electron beam welding tank is designed. Tests show that the set of performance indicators of the fuel tank meets the design goals to meet the actual needs of welding process.

Comparative study of generation characteristics of CdS crystal laser pumped by low- and high-energy electron beams

A CdS crystal has been excited by radially converging pulsed electron beam with an electron energy of up to E ≈ 18 keV, a beam current density at the target of up to 4 kA/cm2, and a pulse full width at half maximum within τ ≈ 12–100 ns. For comparison, the same crystal was pumped by electrons with E = 170 keV at τ = 2.2 ns. A specific distinctive feature of the excitation by powerful low- and high-voltage electron beams is the appearance of previously unreported long-wavelength generation with a peak at λ ≈ 535 nm in the electron-hole plasma band. In the region of the interband transition with a peak at λ ≈ 515 nm, the generation spectra are similar to those known from the literature.

Beam quality test technology and devices of electron beam welding

The electron beam four-dimensional quality test system was developed targeted at the 5–100 mA electron beam current of a high-voltage electron beam welding machine. The system includes the control module, sensor module, driver module, and analysis software, which is based on the complex programmable logic device (CPLD). The quality test system obtains the data of quasi-instantaneous power density distribution (QIPDD) of the electron beam by controlling the beam periodically, scanning the surface of a Faraday cup. Fixing the Faraday cup at an X- and Y-axis coordinate position under constant conditions, the three-dimensional graphic of QIPDD of the beam about the data of a single cross-section was showed by using computer reconstruction technology. Several QIPDD of the electron beam cross-section at different working distance in axial direction reconstructed the four-dimensional graphics of the beam.

Effects of Ionizing Radiation on Microbiological Contaminants of Foods

Ionizing radiation can be used in food industry in order to control the number of microbiological contaminants, among others. The sources of irradiation allowed to be used in this respect are: high-voltage electron beams up to 10 MeV, X – rays up to 5 MeV and gamma rays produced from the radioisotopes 60Co and 137Cs. 
 One of the most important properties of irradiation is inactivation of microorganisms, especially pathogens. Gram-negative pathogen bacteria are very sensitive to radiation. As expected bacterial spores are more resistant to ionizing radiation than vegetative cells are. Irradiation also reduces the number of mould populations. Yeasts on the other hand are more radio-resistant than bacteria and moulds and can become the dominant flora of irradiated foods. In what viruses are concerned, ionizing radiation must be accompanied by other treatments in order to be an efficient inactivation method.
 In conclusion, ionizing radiation can be used, at acceptable doses, as a control method in preserving the innocuity of foods.

The influence of the nitrogen-ion flux on structure and ionic conductivity of vapor deposited lithium phosphorus oxynitride films

Thin films of lithium phosphorus oxynitride (Lipon) have been grown using a plasma-assisted, directed vapor deposition (PA-DVD) technique. In this approach, a high voltage electron beam is used to vaporize a Li 3PO 4 source and a supersonic, nitrogen-doped, helium gas jet then transport the vapor towards a substrate. A hollow cathode technique was then used to create an argon plasma just above the substrate. This sufficiently ionized the nitrogen in the gas jet to allow its incorporation into the Li 3PO 4 film reactively forming lithium phosphorus oxynitride. Increasing the nitrogen flux in the gas jet also increased the deposition rate from 113 to 178 nm min −1 for the deposition conditions used here, significantly reduced the pore volume fraction in the films and increased the N/P ratio from 0 to 0.75 as the gas jet nitrogen flux was increased from zero to 4.3 × 10 18 molecules cm −2 s −1. Using substrate rotation, pore and columnar-free dense Lipon films could be grown by this method. The Li-ion conductivity increased from 3.7 × 10 −9 to 5.2 × 10 −7 S cm −1 as the nitrogen concentration was increased from zero to 2.1 × 10 18 molecules cm −2 s −1 and was correlated with an increase in the film's Li/P ratio. An optimum nitrogen flux has been identified. As the nitrogen flux was increased above this value, the Lipon films suffered lithium loss and partial crystallization, resulting in a decrease in their Li-ion conductivity.

The Study on the Time Dependency and the Stability of Cobalt Sulphide Nanoparticles Under an Electron Beam

We report on the synthesis and characterization of cobalt sulphide (CoS(1.097)) nanoparticles using a cobalt tetramethylthiuram disulphide complex as a single-source precursor. To study the effect of reaction time on the optical and morphological properties of the synthesized nanoparticles, aliquots from the reaction mixture were collected after different intervals of time. The absorption spectra were time dependent, with the 5 min aliquot being the most blue-shifted from bulk and the subsequent samples showing a slight shift towards the bulk. Photoluminescence of the nanoparticles showed a single emission wavelength of 341 nm, however, the peak intensity of nanoparticles decreased with reaction time. The morphology of the synthesized nanoparticles was investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high-resolution TEM (HR-TEM). Results from the SEM images showed the formation of spherical CoS(1.097) nanoparticles and the size of the observed nanoparticles increase with increasing reaction time. However, the TEM results showed a change in the morphology of the particles from spherical to wire-like. The change in morphology was thought to be induced by the high voltage electron beam and this was supported by the HR-TEM and optical results.

Proximity Effect Correction for Mask Writing Taking Resist Development Processes into Account

In this paper, a proximity effect correction method for mask fabrication with taking into account resist development processes is proposed. The idea of our method is that the figure size of a developed resist is determined using a suitable function of exposure dose and the normalized deposited energy by backscattering electrons, under the assumption of high acceleration voltage electron beam mask writing. This suitable function should be determined empirically to include the effects of resist development process, and is called development process function in this paper. Methods of deriving the development process function, proximity effect correction equation, and optimum correction dose from the equation are proposed. To check the accuracy of our method, a sample model of development process function is introduced under the condition that the conventional threshold model has an intrinsic error of 8 nm. The method proposed in this paper is found to be able to suppress the correction error of this sample model to less than 1 and 0.2 nm by two and three iterations, respectively. The method proposed in this paper is expected to provide high accuracy proximity effect correction in future mask fabrication.

Nitrogen segregation and blister formation of 316LN austenitic steel during electron beam welding tests for ITER gravity supports

316LN has been widely applied in the design of ITER components, such as shield blanket and gravity supports, due to its excellent corrosion resistance and high strength. The behavior of nitrogen in this steel during welding is important for the mechanical properties of the components. In this study, a focused 150 kv high voltage electron beam with 300 mA beam current has been used to weld 316LN steel under vacuum condition. The microstructure and composition of the welding area were observed and analyzed. The influence of welding on the shock resistance and tensile strength at both room temperature and low temperature were examined. It was found that the mechanical properties are strongly related to the defects formed in the welding process.

Optimal parameters for low and high voltage electron beam welding of AZ series magnesium alloys and mechanism of weld shape and pore formation

The dependence of ultimate tensile strength (UTS) on the parameters of low voltage and high voltage electron beam welding (LV- and HVEBW) has been analyed by changing one factor at a time (COFAAT) and by Taguchi's method for AZ series magnesium alloys. COFAAT is a conventional method for trend analysis of each parameter. However, its cost is high and a long time is needed, and interactions between parameters are ignored. On the other hand, Taguchi's method cannot only reduce the number of experiments, but also provide precise optimum parameters and predicted UTS even when a few data points are lost. According to the results of analysis of variance, the strength of a weldment is affected by oscillation of the beam, the focal position, the welding speed, the accelerating voltage, the beam current and stress relief, in order of impact. The general trend is for the optimum parameters to include a non-oscillating beam, focus at the bottom and no stress relief. With regard to welding speed, accelerating voltage and beam current, there are no specific trends. Finally, the differences in welds between LV- and HVEBW for AZ series forged alloys have been examined to study the mechanism of pore formation, which results from the dissolution of precipitates to reform molecular oxygen. It is also emphasised that the area and shape of the weld cross-section are related to the input power and welding speed.

Lithium phosphorous oxynitride films synthesized by a plasma-assisted directed vapor deposition approach

A plasma-assisted directed vapor deposition approach has been explored for the synthesis of lithium phosphorous oxynitride (Lipon) thin films. A Li3PO4 source was first evaporated using a high voltage electron beam and the resulting vapor entrained in a nitrogen-doped supersonic helium gas jet and deposited on a substrate at ambient temperature. This approach failed to incorporate significant concentrations of nitrogen in the films. A hollow cathode technique was then used to create an argon plasma that enabled partial ionization of both the Li3PO4 vapor and nitrogen gas just above the substrate surface. The plasma-enhanced deposition process greatly increased the gas phase and surface reactivity of the system and facilitated the synthesis and high rate deposition of amorphous Lipon films with the N∕P ratios between 0.39 and 1.49. Manipulation of the plasma-enhanced process conditions also enabled control of the pore morphology and significantly affected the ionic transport properties of these films. This enabled the synthesis of electrolyte films with lithium ion conductivities in the 10−7–10−8S∕m range. They appear to be well suited for thin-film battery applications.

Quantitative experimental studies of spontaneous rotations of bismuth nanoparticles

A phenomenon of spontaneous rotations of Bi nanoparticles is reported. Fourier transform (FT) analysis of the high resolution electron microscopy (HREM) images indicates that the rotations occur by plane after plane gliding rather than a collective movement of the entire particle as a rigid body. The phenomenon rate was studied quantitatively by time resolved transmission electron microscopy (TEM). The origin of the phenomenon as a radiation effect of the high voltage electron beam was excluded by finding the same rates at $200\phantom{\rule{0.3em}{0ex}}\mathrm{kV}$ and $1250\phantom{\rule{0.3em}{0ex}}\mathrm{kV}$ electron beams, below and above the threshold for the knock-on process. The dependence of phenomenon rate on the particles' size was found to be inversely proportional to the particle volume, with a threshold at particle radius of $5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The temperature was found to activate both the probability for a particle to be in the rotating state, and the rotation rate.

Evolution and Control of 2219 Aluminium Microstructural Features through Electron Beam Freeform Fabrication

Electron beam freeform fabrication (EBF3) is a new layer-additive process that has been developed for near-net shape fabrication of complex structures. EBF3 uses an electron beam to create a molten pool on the surface of a substrate. Wire is fed into the molten pool and the part translated with respect to the beam to build up a 3-dimensional structure one layer at a time. Unlike many other freeform fabrication processes, the energy coupling of the electron beam is extremely well suited to processing of aluminum alloys. The layer-additive nature of the EBF3 process results in a tortuous thermal path producing complex microstructures including: small homogeneous equiaxed grains; dendritic growth contained within larger grains; and/or pervasive dendritic formation in the interpass regions of the deposits. Several process control variables contribute to the formation of these different microstructures, including translation speed, wire feed rate, beam current and accelerating voltage. In electron beam processing, higher accelerating voltages embed the energy deeper below the surface of the substrate. Two EBF3 systems have been established at NASA Langley, one with a low-voltage (10-30kV) and the other a high-voltage (30-60 kV) electron beam gun. Aluminum alloy 2219 was processed over a range of different variables to explore the design space and correlate the resultant microstructures with the processing parameters. This report is specifically exploring the impact of accelerating voltage. Of particular interest is correlating energy to the resultant material characteristics to determine the potential of achieving microstructural control through precise management of the heat flux and cooling rates during deposition.

Paraxial gas-cell focusing of relativistic electron beams for radiography

Summary form only given. A quantitative description of the underlying physics governing the operation of pulsed-power driven, gas-filled, paraxial diodes is presented. Gas-filled focusing cells are routinely used to transport high energy density electron beams for use in flash X-ray radiography experiments. Intense X-rays are generated when the high current (10-30 kA) and high voltage (3-10 MeV) electron beam stops in a high atomic number target and creates bremsstrahlung radiation. The radiation spot and dose are critically dependent on the beam characteristics at the target. The paraxial diode acts as a 1/4 betatron focusing lens with a focal length F proportional to the square root of the beam energy and inversely proportional to the square root of the net current (beam+plasma) in the gas cell, F/spl prop/(/spl gamma//I/sub net/)/sup 1/2/. The time integrated radiation spot is determined both by finite beam emittance and by focal sweeping due to time variations in net current. The beam radius, focal plane, emittance, paraxial dose and time-integrated spot are calculated via particle-in-cell simulations with the Lsp code. The calculated radiation focal plane, spot and dose are compared to data obtained by the Atomic Weapons Establishment from a variety of experimental configurations. Suggestions to improve the X-ray intensity are presented.

Low-voltage electron beam lithography resist processes: top surface imaging and hydrogen silisesquioxane bilayer

A hydrogen silisesquioxane (HSQ) bilayer process and a top surface imaging (TSI) process are investigated for application as low-voltage electron beam resist systems. Namatsu, van Delft, and others have reported printing exceptionally small features using high-voltage electron beam exposure of HSQ at high-exposure doses (~2000 µC/cm2 at 100 kV). The shallow penetration depth of low-voltage electrons results in greatly reduced dose requirements, and smooth, high-resolution images are generated at 1 kV with an exposure dose of less than 60 µC/cm2. HSQ's high silicon content enable it to be used in a bilayer form utilizing reactive ion etching with an oxygen plasma, thus generating high aspect ratio images. TSI has been studied in the past by numerous researchers at low voltages using various TSI schemes. We investigate the use of a chemically amplified TSI resist process based on poly (t-BOC-hydroxystyrene). The effect of base quencher loading in the resist formulation on line edge roughness and resolution is investigated, and is found to have a dramatic influence. High-resolution, high aspect ratio images are printed down to 40 nm, and exhibit only moderate levels of line edge roughness. Furthermore, proximity effects at 1, 2, and 3 kV are examined and compared to simulation.

Property improvement of stainless-steel-base surface composites fabricated by high-energy electron-beam irradiation

This is a study on the fabrication of surface composites of SiC, TiC particulates, and AISI 304 substrate by high voltage electron beam irradiation. Using CaF2 powders as flux, two kinds of surface composites were fabricated for a comparative analysis of the microstructural modification and mechanical properties. Through the employed process, the powders and substrate surface were melted and surface composite layers were successfully formed in both cases. In the specimen fabricated with SiC powders, a volume fraction of Cr23C6 particles (−22 vol.%) were homogeneously distributed along solidification cell boundaries. The large amount of Cr23C6 particles in combination with solid solution hardening of Si in the matrix resulted in the improved hardness and wear resistance of the surface composite layer, that are 2 to 3 times those of the substrate. In the specimen fabricated with SiC and Ti+SiC powders, TiC and Cr23C6 particles were precipitated without precipitation of SiC.

Measurements of electron emission uniformity from cathodes in high-voltage electron beam diodes

Spatial uniformity of electron emission from velvet cathodes has been measured by observing the distribution of electrons hitting the anode in a planar high-voltage diode. It is shown that unless all electrons move parallel to the diode axis, the electron distribution measured at the anode does not represent the cathode emission pattern. Here, parallel trajectories were achieved by applying a strong, uniform axial magnetic field. A 5 ns gated ICCD camera recorded light from a fast anode scintillator. The emission from two brands of velvet was found to be mostly concentrated in small spots with density of about 55/cm2. The pixel-to-pixel standard deviation of the emission amounted to at least 16%.

A new nanocomposite resist for low and high voltage electron beam lithography

A novel nanocomposite photoresist was synthesized and characterized for use in both low and high voltage electron beam lithography. This resist system is shown to display the ideal combination of both enhanced etch resistance and enhanced sensitivity required to satisfy both low and high voltage patterning applications. Resist sensitivity was enhanced by the direct incorporation of a photoacid generating monomer into the resist polymer backbone while the etch resistance of the material was improved by copolymerization with a POSS containing monomer.