Vacuum Electron Beam Research Articles

Secondary electron emission yield from high aspect ratio carbon velvet surfaces

The plasma electrons bombarding a plasma-facing wall surface can induce secondary electron emission (SEE) from the wall. A strong SEE can enhance the power losses by reducing the wall sheath potential and thereby increasing the electron flux from the plasma to the wall. The use of the materials with surface roughness and the engineered materials with surface architecture is known to reduce the effective SEE by trapping the secondary electrons. In this work, we demonstrate a 65% reduction of SEE yield using a velvet material consisting of high aspect ratio carbon fibers. The measurements of SEE yield for different velvet samples using the electron beam in vacuum demonstrate the dependence of the SEE yield on the fiber length and the packing density, which is strongly affected by the alignment of long velvet fibers with respect to the electron beam impinging on the velvet sample. The results of SEE measurements support the previous observations of the reduced SEE measured in Hall thrusters.

EFFECT OF HEAT TREATMENT ON (Cr, Fe)7C3/γ-Fe COATINGS IN SITU SYNTHESIZED BY VACUUM ELECTRON BEAM IRRADIATION

(Cr, Fe)7C3/[Formula: see text]-Fe composite layer has been in situ synthesized on a low carbon steel surface by vacuum electron beam VEB irradiation. The synthesized samples were then subdued to different heat treatments to improve their impaired impact toughness. The microstructure, impact toughness and wear resistance of the heat-treated samples were studied by means of optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), microhardness tester, impact test machine and tribological tester. After heat treatment, the primary and eutectic carbides remained in their original shape and size, and a large number of secondary carbides precipitated in the iron matrix. Since the Widmanstatten ferrite in the heat affected zone (HAZ) transformed to fine ferrite completely, the impact toughness of the heat-treated samples increased significantly. The microhardness of the heat-treated samples decreased slightly due to the decreased chromium content in the iron matrix. The wear resistance of 1000[Formula: see text]C and 900[Formula: see text]C heat-treated samples was almost same with the as-synthesized sample. While the wear resistance of the 800[Formula: see text]C heat-treated one decreased slightly because part of the austenite matrix had transformed to ferrite matrix, which reduced the bonding of carbides particulates.

Excess oxygen limited diffusion and precipitation of iron in amorphous silicon dioxide

In micro- and nano- electronic device fabrication, and particularly 3D designs, the diffusion of a metal into sublayers during annealing needs to be minimized as it is usually detrimental to device performance. Diffusion also causes the formation and growth of nanoprecipitates in solid matrices. In this paper, the diffusion behavior of low energy, low fluence, ion implanted iron into a thermally grown silicon oxide layer on silicon is investigated. Different ion beam analysis and imaging techniques were used. Magnetization measurements were also undertaken to provide evidence of nanocrystalline ordering. While standard vacuum furnace annealing and electron beam annealing lead to fast diffusion of the implanted species towards the Si/SiO2 interface, we show that furnace annealing in an oxygen rich atmosphere prevents the diffusion of iron that, in turn, limits the growth of the nanoparticles. The diffusion and particle growth is also greatly reduced when oxygen atoms are implanted in the SiO2 prior to Fe implantation, effectively acting as a diffusion barrier. The excess oxygen is hypothesized to trap Fe atoms and reduce their mean free path during the diffusion. Monte-Carlo simulations of the diffusion process which consider the random walk of Fe, Fick's diffusion of O atoms, Fe precipitation, and desorption of the SiO2 layer under the electron beam annealing were performed. Simulation results for the three preparation conditions are found in good agreement with the experimental data.

Diamond film, single-layer carbon nanosheet film and diamond/carbon nanosheet composite film synthesis and field emission performance comparison

A series of diamond films, single-layer carbon nanosheet (SCNS) films and diamond/carbon nanosheet (D/CNS) composite films have been prepared on the heavily-doped n-type silicon substrate by using microwave plasma chemical vapor deposition (MPCVD) techniques and vacuum electron beam evaporation techniques. The films were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction(XRD), Raman spectroscopy. Field emission test results showed that diamond film, SCNS film and D/CNS composite film respective field emission current density is 0.004 mA/cm2 (there's almost no electron emission), 0.45 mA/cm2 and 3.21 mA/cm2 at an electric field of 7.2V/μm. This means that the field emission maximum current density of D/CNS composite films is 7.1 times that of SCNS films at an electric field of 7.2 V/μm. At the same time the D/CNS composite film exhibits the advantage of improved reproducibility and long term stability. Diamond layer can effectively improve the field emission characteristics of CNS film. The reason may be due to the diamond film acts as the electron acceleration layer, meanwhile, the heterogeneity of diamond and CNS material could lead to lowering of the interfacial potential barrier.

Optical and structural constants of CdS thin films grown by electron beam vacuum evaporation for solar cells

The structural and optoelectronic properties of polycrystalline cadmium sulfide (CdS) films grown by electron beam evaporation have been optimized through thermal annealing treatment. The direct band gap is decreased from 2.57eV to 2.43eV with the treatment and various optical, dielectric, material characteristic energy parameters/constants have also been determined. X-ray diffraction (XRD) analysis revealed the zinc blende cubic structure of the films and an indication of phase change is observed at 500°C. The electrical conductivity is found to be increased with annealing temperature while the Fourier transform infrared (FTIR) analysis revealed an increment in IR transmittance. The surface morphology is found to be homogeneous with uniform circle-shaped grains and the presence of Cd and S elements in the grown film is confirmed by the energy-dispersive spectroscopy analysis. From optimized results, it can be figured that the CdS films annealed at 500°C are suitable for window and hole-blocking layers in CdTe-based and perovskite solar cells respectively.

Continuous electron beam melting technology of silicon powder by prefabricating a molten silicon pool

We successfully achieved the continuous melting of silicon powder in a vacuum electron beam melting system. The characteristic of electron beam melting of silicon powder was revealed by comparing the three different approaches to prefabricate the molten silicon pool. The application of silicon block can be regarded as the most efficient method to prefabricate a stable molten silicon pool. Afterward, the silicon powder was added into the molten silicon pool at different rates by a spiral silicon powder feeding device. Finally, all of the silicon powder was melted completely. Although the P removal efficiency decreases with increasing powder feeding rate during the powder feeding process, an appropriate increase in the powder feeding rate is not only beneficial to improve the melting efficiency of silicon powder but also conductive to the improvement in uniformity of the obtained silicon ingot. Therefore, the powder feeding rate of 10 g/min was the best option in this study. Compared with the melting of silicon block, which has been wildly applied, this continuous powder feeding process can be beneficial to saving smelting time and the total cost.

Peculiarities of Electron-Beam Formation of Hydrophobic and Superhydrophobic Coatings Based on Hydrocarbons of Various Molecular Weights and PTFE

The paper studies the possibility of superhydrophobic coatings formations at exposure of powder mixture of polytetrafluorethylene and hydrocarbons having various molecular weights to low-energy electron beam in vacuum. It is shown that paraffin and PTFE based thin composite coatings may be characterized by superhydrophobic properties. The superhydrophobic properties are attained due to low surface energy of the fluorine-containing component and structured surface due to peculiarities of composite layer formation. The chemical processes observed in electron beam exposed area determine the molecular structure, morphology and the contact angle of thin organic coatings deposited. It is shown that high-molecular-weight hydrocarbon compounds should not be recommended for vacuum electron-beam deposition of superhydrophobic thin coatings because of deep changes in the molecular structure exposed to electron beam. These processes are responsible for high degree of unsaturation of the thin layer formed and for occurrence of oxygen-containing polar groups. The influence of substrate temperature on molecular structure, morphology and hydrophobic properties of thin coatings deposited is investigated. Potentially such coatings may be applied for deposition on the surface of metal capillaries used in biotechnological analyzers.

On the Principles of Tweaking Nanostructure Fabrication via Focused Electron Beam Induced Processing Combined with Catalytic Growth Processes

Novel pathways to use a focused electron beam in ultrahigh vacuum in combination with catalytic growth protocols are explored for the fabrication of well-defined nanostructures. Thereby, the basic process is the local deposition of material from different precursor molecules (Co(CO)3 NO, Fe(CO)5). This can be realized with a focused electron beam by direct deposition of the precursor or by a chemical modification of the substrate, such that it becomes activated toward the decomposition of the precursor. For both methods, autocatalytic growth (AG) processes can occur, yielding the deposition of additional material. Interestingly, significantly different chemical selectivities for the two precursors are found, which can drastically change upon subtle changes of the surface. It is demonstrated that AG can be tweaked by the choice of the substrate/precursor combination. One possibility to quench catalytic activity of a substrate is the preparation of a thin layer of organic molecules, here porphyrins, which enables the fabrication of hybrid metal–organic nanostructures with line widths below 20 nm. Based on these findings, corresponding techniques are developed which exploit (auto)catalytic effects for the controlled fabrication of nanostructures. These results indicate that every substrate is applicable to electron beam induced surface activation by preparation of a thin porphyrin layer.

Design of Electron Beam Welding Vacuum Chamber for Collar Rings in CFETR Windows

China Fusion Engineering Test Reactor window collar has a very complex three-dimensional structure, because of its large size, in the window and collar welding cannot be completed after the overall processing, therefore, requires that the welding ring has deformation of small, high precision welding, and reliable welding quality. As a kind of high-energy beam welding method, vacuum electron beam welding can ensure the welding quality of the collar of the vacuum chamber. Therefore, a vacuum electron beam welding system will be used to weld the window collar of the vacuum chamber. The vacuum electron beam welding system consists of vacuum chamber, electron beam welding gun, movement system, pumping system and other major components. Because the size of the vacuum chamber is 7200 × 3550 × 2600 mm, its working stability is very important. Therefore, the structure of the vacuum chamber is designed and its working state is simulated and analyzed by ANSYS finite element analysis. The structure of the vacuum chamber is optimized. And the pumping time of this vacuum pumping system is calculated in detail. The design provides a reference.

Effect of treatment in weld surface on fatigue and fracture behavior of titanium alloys welded joints by vacuum electron beam welding

The effect of treatment in weld surface on four-point bend fatigue properties and fracture characteristic of Ti–6.5Al–2Zr–1Mo–1V alloy by vacuum electron beam welding were tested and analyzed. When the excess weld metal and excess penetration are removed, the high fatigue strength of joints can be obtained. When the excess weld metal and excess penetration were not removed, the fatigue strength of joints is about 40% of yield strength of base metal. Two kinds of fatigue crack initiations can be observed under the upper surface of joint, which show the obvious local tearing fracture morphology and bulk inclusions or compounds morphology.

Creation of the nanostructured superhard and heatproof layers on die steels under influence of intensive electron beams in vacuum

Studying and comparing microstructure and microhardness of boride layers formed on die D2 steel by using different methods – electron beam borating with continuous and pulsed beams under vacuum. The created layers have a heterogeneous structure combining hard and plastic components resulting in decrease of boride layer embrittlement.

High sensitivity surface plasmon resonance (SPR) refractive index sensor in 1.5 μm

A surface plasmon resonance (SPR) based sensor is proposed and demonstrated for operation in the 1500 nm region. The sensor operates by the immersion of microfibers with a 25-μm diameter waist in chemical solutions that have varying external effective refractive indices. The sensor is fabricated using a homemade single-mode tapered fiber with a uniform waist coated on all sides with a gold layer approximately 45 nm thick by means of a vacuum electron beam evaporator machine. The transmission dips in the sensor’s optical spectrum are highly responsive to any perturbations in the external medium refractive index, thus providing high sensitivity. The proposed sensor system has multiple potential applications in biological and chemical constituent and reaction measurements.

Study and Fabricate of Reflectance Coating for UV Lithography Machine Arc Lampshade

As one of the key components in lithography, the UV light source has very high demands for wavelength of source and energy. To meet the requirements of UV light source, it demands UV reflectance coating prepared on 78mm Mg-Al alloy paraboloid lampshade . Based on design theory of film, H4 and SiO2 were selected as high and low refractive index materials respectively, and with the help of TFCalc, adopting electron beam vacuum coating method, the reflectance coating was prepared, which satisfied the requirements of reflectivity greater than 98.5% within band of 365-436nm in the case of 0o-45o incident angles. First the reflective band width was broadened through the coating stack; then according to the thickness distribution of film, compensation baffle was designed and modified, which ensured the uniformity of reflectance coating in the lampshade. And last, firmness of coating was strengthened and the reflectivity in the required band was improved by depositing one bonding layer of metal between Mg-Al alloy and dielectric film. By repeated trials, coating absorption problem was solved by changing the process parameters and coating quality of film was improved with the use of ion source assisted deposition, finally the UV film meets the requirements for use.

Indigenous Manufacturing realization of TWIN Source

TWIN source is two RF driver based negative ion source that has been planned to bridge the gap between single driver based ROBIN source (currently operational) and eight river based DNB source (to be operated under IN-TF test facility). TWIN source experiments have been planned at IPR keeping the objective of long term domestic fusion programme to gain operational experiences on vacuum immersed multi driver RF based negative ion source. High vacuum compatible components of twin source are designed at IPR keeping an aim on indigenous built in attempt. These components of TWIN source are mainly stainless steel and OFC-Cu. Being high heat flux receiving components, one of the major functional requirements is continuous heat removal via water as cooling medium. Hence for the purpose stainless steel parts are provided with externally milled cooling lines and that shall be covered with a layer of OFC-cu which would be on the receiving side of high heat flux. Manufacturability of twin source components requires joining of these dissimilar materials via process like electrode position, electron beam welding and vacuum brazing. Any of these manufacturing processes shall give a vacuum tight joint having proper joint strength at operating temperature and pressure. Taking the indigenous development effort vacuum brazing (in non-nuclear environment) has been opted for joining of dissimilar materials of twin source being one of the most reliable joining techniques and commercially feasible across the suppliers of country. Manufacturing design improvisation for the components has been done to suit the vacuum brazing process requirement and to ease some of the machining without comprising over the functional and operational requirements. This paper illustrates the details on the indigenous development effort, design improvisation to suits manufacturability, vacuum brazing basics and its procedures for twin source components.

Thermal annealing induced physical properties of electron beam vacuum evaporated CdZnTe thin films

The thermal annealing induced physical properties of electron beam vacuum evaporated CdZnTe thin films have been investigated in the present work. The films of thickness 300nm were deposited on indium tin oxide coated glass substrates followed by thermal annealing at 100°C, 200°C and 300°C. The pristine and annealed films were subjected to the X-ray diffraction, UV–Vis spectrophotometer, Fourier transform infrared (FTIR) spectroscopy, source meter and Energy-dispersive spectroscopy for structural, optical, electrical and elemental composition analysis respectively. The structural analysis revealed that the films have cubic oriented polycrystalline structure with preferred orientation (111). The optical absorbance is found to increase with annealing while optical energy band gap is observed to decrease. Different optical constants like absorption coefficient, refractive index, dielectric constants and energy loss functions have been calculated using Herve-Vandamme model, dielectric theory, Swanepoel model and discussed. The FTIR study indicates the absorption intensity is increased with annealing temperature. The elemental analysis revealed to the presence of Cd, Zn and Te elements in the deposited films. The current-voltage tests show that the electrical conductivity is increased with thermal annealing. The results revealed to a demanding behavior of annealed films for the solar cell applications.

Antibacterial polyurethane materials with silver and copper nanoparticles

New biologically active polyurethanes with silver and copper nanoparticles in their composition were prepared by saturation of liquid polyether (the initial component for polyurethane synthesis) with nanoparticles (Ag, Cu), followed by synthesis of polyurethane. The results of these studies allow consideration of these materials as medical suppliers with antibacterial properties. The main problem of their creation is uniform distribution of the metal nanoparticles inside the polymer matrix without changing the physico-chemical properties of the latter. Obtaining of metal nanoparticles’ colloid in a liquid polyoxytetramethylene glycol, MM 1000 was carried out by electron beam evaporation technology and vacuum deposition. This method allowed creating, on the basis of obtained colloids, the metal-containing polyurethane materials with targeted properties and structure that are determined by diisocyanates and chain extenders nature. Biological study has shown that polyurethanes containing Cu and Ag nanoparticles possess bactericidal/bacteriostatic effect against bacteria, fungi and yeast-like fungi. Polymer samples did not exhibit toxicity to the tissue culture cells and there were no biodegradation products observed in the culture medium. Resulting biologically active metal-containing polyurethane materials can be processed into products for medical purposes (implants, drug delivery systems, antimicrobial coatings for biomedical devices and antimicrobial packaging) by standard methods of polyurethane processing, since the presence of metal nanoparticles in their composition does not affect the physical properties of the polymer.

Microstructures and Mechanical Properties of Weld Metal and Heat-Affected Zone of Electron Beam-Welded Joints of HG785D Steel

Vacuum electron beam welding (EBW) process was employed to butt weld 10-mm-thick HG785D high-strength steels. The penetration into the steel was adjusted by beam current. Microstructures at weld metal and heat-affected zone (HAZ) regions were comparatively observed. Mechanical properties of the EBWed joints including Vickers hardness, tensile and Charpy impact tests were evaluated. The results indicated that microstructures at the weld metal consisted of coarse lath martensite and a small amount of acicular martensite, while that in the HAZ was tempered sorbite and martensite. The grain size in the weld metal was found to be larger than that in the HAZ, and its proportion in weld metal was higher. The hardness in the weld metal was higher than the HAZ and base metal. The tensile strength and impact toughness in the HAZ was higher than that in the weld metal. All the behaviors were related to microstructure evolution caused by higher cooling rates and state of base metal. The fracture surfaces of tensile and impact tests on the optimized joint were characterized by uniform and ductile dimples. The results differed significantly from that obtained using arc welding process.

Enhanced structural, electrical and optical properties of evaporated CdZnTe thin films deposited on different substrates

CdZnTe thin films of thickness 300nm were deposited on glass, ITO, FTO and silicon wafer at room temperature employing electron beam vacuum evaporation. These deposited films were analyzed using XRD, source meter and UV–Vis spectrophotometer to investigate structural, electrical and optical properties, respectively. The films are found to be polycrystalline in nature with zinc-blende cubic structure and evaluated structural parameters show significant effect of used substrates. The electrical study shows that the conductivity is maximum for films deposited on FTO substrate. The optical analysis shows wide transmittance with the energy band gap in the range 1.71–2.28eV.

Bright blue electroluminescence of diamond/CeF3 composite films

Diamond/CeF3 composite film (DCCF) electroluminescence devices was fabricated on highly doping n-type silicon substrates by using plasma chemical vapor deposition techniques and vacuum electron beam evaporation techniques. The films were characterized by field emission scanning electron microscopy (FE-SEM), Energy dispersive spectrum (EDS), X-ray diffraction (XRD) and electroluminescence (EL) spectrum. The EL spectrum of DCCFs shows that a strong broad peaks are located at 440 nm, and its EL brightness of the device can reach 10 cd/m2 at a forward applied voltage of 120 V. The blue light emitting peak is assigned to the transitions from the excited 5d state to 4f (2F5/2) and 4f (2F7/2) states of Ce3+ ions, respectively.

Numerical analysis of fluid transport phenomena and spiking defect formation during vacuum electron beam welding of 2219 aluminium alloy plate

In this paper, a 3D mathematical model is proposed to investigate the physical transport phenomena in weld pool and vapour plume during the stationary vacuum electron beam welding on 2219 aluminium alloy plate. Three beam current cases are employed to investigate the heat transfer, fluid flow, keyholing, keyhole backfilling and collapsing processes, and the resulting spiking defect and residual crater. In the model, a keyhole-tracing heat source is adopted to simulate the energy interactions between electron beam and material with the help of VOF technique. Results indicate that the beam profile and heat flux distribution decreases the growing speed of keyhole dimensions. The increase of beam current raises the evaporation intensity, keyhole wall temperature, keyholing depth and keyhole instability. On the premise of same heating time, a larger beam current produces a spiking defect in partially-penetrated weld. Finally, all the simulation results are validated against experiments.