Electron Beam Heating Research Articles

Novel in situ method for locating virtual source in high-rate electron-beam evaporation

The concept of virtual source simplifies calculation of thickness distribution on extended substrates in high rate vacuum coating employing electron-beam heating. The height of the point (virtual source), from which vapor can be assumed to emanate in accordance with Knudsen’s cosine law, to yield the experimentally obtained thickness distribution, is calculated and this establishes the position of virtual source. Such as post facto determination is cumbersome as it is valid for the prescribed material evaporating at a certain rate in a specified geometry. A change in any of these entails a fresh measurement. Experimenters who use a large number of materials and deposit at different rates therefore have to carry out a number of trials before they can locate the virtual source at the desired deposition parameters. An in situ method for obtaining virtual source position can go a long way in reducing the labor of these experiments. A novel in situ method is described to locate the virtual source.

On the occurrence of blue asymmetry in chromospheric flare spectra

We present observations of optical spectra of a flare in which blue line asymmetry was seen for more than 4 min close to the flare onset. The maximum blue asymmetry coincided with the maximum of a hard X-ray and microwave burst. We discuss possible interpretations of the blue asymmetry and conclude that the most plausible one is electron-beam heating with return current. Although this process predicts downflows in the lower transition region and upper chromosphere, its ultimate effect on the line profiles can be blue asymmetry: the upper layers moving away from us absorb the radiation of the red peak thus lowering its intensity in comparison to the blue one.

Characteristics of ta2O5 thin film prepared by electron beam heating method

AbstractA Ta2O5 film formed by ϵ‐beam evaporation (EB‐Ta2O5) was nonstoichiometric because of oxygen deficiency, resulting in electron trapping. As a result, the dielectric constant was higher than that of bulk material. the trapped fixed‐charge density increased with a decrease of film thickness.When the film was 300 nm, the trapped fixed Charge density was as high as 1016 cm−3. However, when the film was thicker than 300 nm, it decreased rapidly. the dielectric constant approached the bulk value as the film thickness increased, and the film resistance was low because of oxygen deficiency. When the film was 300 nm, the resistivity p was 107 − 108 ω ‐cm (5 × 105 V/cm). When the electric field reached about 7 × 105 V/cm, only the current density increased in spite of the slight increase of the electrical field.When the film was thicker than 300 nm, the resis tivity increased and the clamp field became unclear with an increase of thickness. an EL (electroluminescent) device was formed using the EB‐Ta2O5 film sandwiched with SiO2 films as the luminescent film. the luminance of the device was 100 cd/2. the luminescence spectrum had peaks at 380, 430, 475, and 540 nm, indicating that there were energy levels at 3.2, 2.9, 2.6, and 2.3 eV.

Measurement of Metastable Population in Gadolinium Atomic Beam by Resonance Photoionization

Population of metastable levels in a gadolinium atomic beam produced by electron beam heating were measured using the resonance photoionization technique. The population followed the Boltzmann dist...

Removal of the plasma contained in an atomic beam produced by electron beam heating

Removal of the plasma contained in a gadolinium atomic beam produced by electron beam heating was investigated. A positive or negative electric potential was applied to the plasma removal electrodes which were a pair of parallel electrodes put along the atomic beam. When a positive potential was applied to the plasma removal electrodes, the plasma could not be removed at high evaporation rates. On the other hand, the plasma could be removed by applying a high negative potential to both removal electrodes, even at high evaporation rates. The potentials applied to the electrodes required to remove the plasma were estimated using the model that a plasma at ground potential flows with the atomic beam; ions are extracted from the plasma by negatively biased removal electrodes. The estimated potentials required to remove the plasma agreed well with experimental values.

Microstructure of pressureless-sintered Al2O3-24 vol% ZrO2 composite studied by high-resolution electron microscopy

The microstructure of an Al2O3-24 vol% ZrO2 composite prepared by pressureless-sintering was investigated by high-resolution electron microscopy. The composite was formed of homogeneously dispersed ZrO2 and Al2O3 grains with average sizes of 0.3 and 0.5 μm, respectively. Most ZrO2 grains had a monoclinic structure, but a few ZrO2 embedded in Al2O3 grains were a tetragonal structure. At interfaces between ZrO2 with a lamella-type twin structure and Al2O3, microcracks were observed, in addition to strain fields in the Al2O3 matrix. Complex twin structures accompanied by dislocations were observed in ZrO2 with a spherical shape. In in situ observations with electron-beam heating, it was found that a crack propagated along an Al2O3/ZrO2 interface and stopped at the place where a tetragonal ZrO2 had undergone a structural change to monoclinic ZrO2.

Kinetics of the formation of cobalt disilicide at high temperature under rapid electron beam heating

Kinetics of the formation of cobalt disilicide at high temperature under rapid electron beam heating

Growth and crystallographic, surface and defect structures of antimony particles deposited in a high-resolution transmission electron microscope

Sb fine particles vacuum-deposited by in situ electron beam heating in an electron microscope were investigated by high-resolution transmission electron microscopy. Round amorphous particles less than 40 nm in size were formed far from the evaporation source, and crystalline particles having definite crystal habits near the source. Observed wedge-shaped crystallites have smooth (110), (111) and/or (112) surfaces, where lattice relaxation and superlattice structure cannot be seen. Stacking faults represented by ab ca/ca bc/bc ab, which are caused by slippings by a glide vector of 1 3 [ 112]a 0 , are found in particles having the normal sequence ab ca bc ab ca bc ab ca bc, where a, b and c denote atomic layers in the rhombohedral structure.

Characterization of Gadolinium Plasma in Gadolinium Vapor at High-Rate Evaporation by Electron Beam Heating

The characteristics of gadolinium plasma in gadolinium vapor at high-rate evaporation using electron beam heating have been measured with Langmuir probes. Electron temperature was lower than 0.1 eV and close to the atomic excitation temperature, which was much lower than the evaporation surface temperature. Ion flux ratio to vapor flux was 0.4%. This value agreed well with the estimated value on the assumption that the atoms are ionized by collision with high-energy electron beams.

Emissivity of silicon at elevated temperatures

The temperature dependences of the spectral and total hemispherical emissivities of silicon have been experimentally determined, by using a technique which combines isothermal electron beam heating with in situ optical measurements. Emission spectra were used to deduce the absorption coefficient for phosphorus-doped silicon samples for wavelengths between 1.1 and 1.6 μm, in the temperature range from 330 to 800 °C. For lightly doped samples, the data show good agreement with a model which includes the effects of the various phonon-assisted processes involved in interband transitions in silicon, as well as the free-carrier absorption. For heavily doped samples the agreement was less satisfactory, possibly because of inadequacies in the model for free-carrier absorption. It was shown that reflection spectra can also be used to determine the absorption spectrum, for the range where the absorption coefficient lies between 1 and ∼70 cm−1. By fitting the theoretical model to the absorption coefficients derived from the reflection spectrum, it is possible to deduce the temperature of a sample, which is especially useful for temperatures less than 300 °C, where the thermal emission is very weak. The total hemispherical emissivity of the specimens was determined from the input electron-beam power densities and the measured temperatures. The total emissivity of a 390-μm-thick specimen of lightly doped silicon rises from 0.12 at 280 °C to a limiting value of 0.7 at 650 °C. This behavior is a consequence of the increase in the free-carrier concentration with the temperature. For heavily doped specimens the total emissivity remains approximately constant at ∼0.7 between 200 and 800 °C because the carrier concentration is high even at room temperature, and the additional thermal generation of carriers produces an insignificant change in the total emissivity.

Atomic-level imaging of intercalation reactions by DHRTEM

The deintercalation and intercalation reactions of two model intercalation systems, Hg xTiS 2 and (NH + 4) y' (NH 3) y″ TaS y'- 2, respectively, have been investigated by dynamic high resolution transmission electron microscopy at a time resolution of 0.03 s. Both reaction types were directly observed at the atomic-level, including the first dynamic atomic-level observation of intercalation reaction processes. Three types of mechanisms were observed for the deintercalation of mercury from the TiS 2 layers in Hg x TiS 2: (1) deintercalation of complete mercury-filled layers, (2) deintercalation of mercury via edge dislocations and (3) deintercalation of mercury islands. The intercalation of ammonia into 2HtaS 2 was observed in situ using an environmental cell. The intercalation reaction proceeded inward from the outer basal planes of TaS 2. Partial intercalation of inner TaS 2 layers occurred, and these layers could be deintercalated by sufficient electron-beam heating. Both intercalation and deintercalation processes proceeded by the advance and retreat, respectively, of guest-edge dislocation fronts.

Thermal Design and Experimental Analysis of Laser and Electron Beam Hardening

Dimensionless correlations for an easy prediction of the hardened depth in electron and laser beam heating treatments are derived from two analytical thermal models. Electron beam heat treating is carried out on 9Cr-2Mo and C40 steels. Effects of the translation speed and the spot dimensions were taken into account. The fairly good agreement between analytical and experimental data suggests that the proposed correlations can be used in applications.

Metastable states’ population densities in Gd atomic beam at high-rate evaporation by electron beam heating

Metastable states’ population densities in gadolinium atomic beams, which were produced by an axial electron beam gun, were measured by laser absorption spectroscopy at the atomic densities on the order of 1012 atoms/cm3. The following results were obtained. (1) The atomic excitation temperature derived from the metastable states distributions is considerably lower than the evaporation surface temperature. With increasing evaporation rates, the atomic excitation temperature decreased to about 500 K. (2) The densities of both ground and first metastable states increased linearly with the deposition rates as measured by a quartz crystal sensor on the beam axis, which indicates that the atomic beam is almost free from the cluster formation caused by rapid expansion into a high vacuum.

Synthesis of nanophase materials by electron beam evaporation

A new nanophase materials preparation system using electron beam heating to vaporize materials in inert or reactive gaseous environments has been developed. With this system, a wide variety of materials can be produced in nanophase form with minimum contamination. Besides enabling the production of pure metals, including refractory materials, the system is designed to produce alloys and multicomponent materials by simultaneous evaporation of two or more elements. The electron beam position and dwell time are set by computer, allowing great control of the evaporation conditions. Results obtained to date indicate great promise for obtaining increased yields and smaller grain sizes that typically obtainable when nanophase materials are produced using resistive heating. A description of nanophase γ-Al 2O 3, produced with a mean grain size of approximately 2.5 nm, is given as a demonstration of the capabilities of the system.

Behaviour of adsorbed oxygen during rapid electron-beam heating of Ta/Ti bilayers on single-crystal silicon

Silicidation of thin films of Ta/Ti bilayers on silicon substrates, in the temperature range 750–1000 °C, using rapid electron-beam heating is described. The redistribution of adsorbed oxygen in the metal films and its effect on the formation of the suicide is examined. It was found that the silicidation of the bimetallic films proceeded sequentially. First titanium and then tantalum layers were converted into their respective suicides. During the growth of titanium disilicide, adsorbed oxygen moved to the interface between the unreacted tantalum film and the grown titanium disilicide, where it formed a thin layer of silicon dioxide. The silicon dioxide barrier inhibited silicon diffusion and the tantalum layer only converted to suicide at temperatures higher than 750 °C which were maintained for a few seconds.

The dynamics of amorphous-to-crystalline interface evolution in ion-implanted polycrystalline silicon

Time-resolved reflectivity measurements have been used to investigate the morphology of an evolving amorphous-crystalline interface during solid phase epitaxial regrowth of an ion-implanted polycrystalline silicon film. Isothermal electron beam heating was used to produce partly regrown specimens for cross-sectional transmission electron microscopy analysis, and this has enabled a direct correlation to be established between the interface shape and the observed reflectivity transients. Using a thin-film optical model of an evolving rough interface, this correlation has enabled interface shapes to be inferred from the reflectivity at higher temperatures, where it is difficult to achieve partial regrowth. For undoped material, smaller grain sizes have been found to lead to rougher interfaces, with regrowth rates typically 20 times slower than for single crystal. At 620 °C, the presence of high concentrations of arsenic results in a smoother interface, but as the regrowth temperature is increased, the interface becomes rougher. The complex interplay between doping, temperature, and initial microstructure is investigated at temperatures up to 850 °C.

Angular Distribution of Gadolinium Vapor Produced by Electron Beam Heating

KEYWORDS: electron beamheatingangular distributiongadoliniumvaporfree expansion vacuum depositionhigh temperatureevaporationdirect simulation Monte Carlo method

Angular Distribution of Gadolinium Vapor Produced by Electron Beam Heating.

Click to increase image sizeClick to decrease image sizeKEYWORDS: electron beamheatingangular distributiongadoliniumvaporfree expansion vacuum depositionhigh temperatureevaporationdirect simulation Monte Carlo method

電子ビーム加熱で生成したウラン準安定原子の占有密度比

The laser induced fluorescence technique has been used to determine the population ratio of three metastable states, 620, 4, 275 and 7, 005cm-1, to the ground state of 238U which was evaporated into vacuum by electron beam heating. The population ratio of metastable states of 620, 4, 275 and 7, 005cm-1 decreased by increasing the temperature of evaporation surface in the range of 2, 700-3, 000K, and the rate of decrease was larger for the metastable states with higher energies. Excitation temperatures of the metastable states, 4, 275 and 7, 005cm-1 were 4, 500 and 3, 300K, respectively, at the surface temperature of melt, 2700K, and were higher than the surface temperature of melt. The excitation temperatures were cooled down rapidly to 2, 800 and 2, 200K, respectively, by increasing the surface temperature to 3, 000K.The experimental results indicate that 238U atoms are excited not only by thermal excitation but also by electron impact excitation. Relaxation of metastable atoms is due to the collision of atoms of which density above the evaporation surface increases with the increase of the surface temperature.

電子供給層と電流制限層を設けたＥＬ素子の発光特性

A large number of electrons can be fixed in S1O2, Al2O3 and Ta2O5 low-resistive insulating films (ρ=107-108 Ωcm at1-5 × 105 V/cm) deposited by the electron beam heating method because these films have oxygen starved states. When an electric field of about 7 × 105 V/cm is applied to the films, the electric field is clamped, and a considerably large current flows, similar to an avalanche phenomenon. By placing these insulating films on both sides of the phosphor film for electron emitting layers, the gradient of the luminance vs voltage curve becomes steep (2300 cd/m2 at 30 V above from threshold voltage). High luminescence (3700 cd/m2 at 1 kHz sine wave voltage) can be obtained by depositing high-resistive insulating SiO2 films of 1012-4014 Ωcm (at 1 × 106 V/cm), as current limiting layers, outside the electron emitting layers. This device worked up to 110 V from the threshold voltage.