Electron Beam Heating Research Articles

Multicomponent surface analysis system combined with high pressure reaction cells for studying metal oxide model catalysts

A three chamber ultrahigh vacuum (UHV) surface analysis system combined with high pressure reaction cells has been designed. It can be used for the preparation and characterization of ordered metal oxide model catalyst surfaces and for the investigation of heterogeneous catalytic reactions there on also under high pressures. The reaction cells are completely separated from the UHV analysis chambers. They can be used for oxidation treatments and reaction studies at total pressures up to 1 bar. A new sample transfer mechanism together with sapphire sample holders and sample heating–cooling stations on the analysis chamber manipulators provides electron beam and resistive sample heating, liquid nitrogen sample cooling, and precise thermocouple temperature control. First experimental results obtained on single crystalline iron oxide dehydrogenation films grown onto Pt(111) substrates are presented. These results demonstrate the capability of the system for in situ investigation of a sample surface using scanning tunneling microscopy, low-energy electron diffraction, Auger electron spectroscopy, photoelectron emission microscopy, and temperature programmed desorption before and after catalytic reactions at high pressures. This single crystal surface science approach provides new insight into the atomic scale surface chemistry of metal oxides under real catalysis conditions.

In-situ TEM observations of tetragonal to monoclinic phase transformation in ZrO 2-2 mol% Y 2O 3 ceramics

In-situ TEM observations of tetragonal to monoclinic phase transformation in ZrO 2-2 mol%Y 2O 3 ceramics were performed under the action of electron beam heating. The results show that the nucleation and growth of m-ZrO 2 martensite and its final morphology are dependent upon the microscopic content and distribution of Y 2O 3. In microareas with lower Y 2O 3 content and homogeneous distribution, the m-ZrO 2 martensite nucleates and grows by twins, finally forming parallel laths. But in microareas with higher Y 2O 3 content and heterogeneous distribution, single plate of m-ZrO 2 martensite is first formed, and simulates the appearance of other martensite plates, finally forming N or Z shaped skeleton.

Oriented Structure and Crystallography of Directionally Solidified LaB6—ZrB2 Eutectic

Directional solidification of LaB6—ZrB2, by use of an electron beam heating technique, yielded oriented ZrB2 fibers in a LaB6 matrix. The average diameter of the ZrB2 fibers was ∼0.2–1.2 µm, with fiber lengths up to 100 µm. Primary platelike LaB6 dendrites formed upon the solidification of an ingot with a composition of LaB6—18 wt% ZrB2. LaB6 was the first phase to nucleate when eutectic growth occurred, and ZrB2 showed nonfaceted growth. For the ingot solidified with planar growth the orientation relations of the phases were as follows: growth direction, [001]LaB6∥[00.1]ZrB2; interfacial plane, (11.0)LaB6∥(11.0)ZrB2.

Emissivity Of Coated Silicon At Elevated Temperatures

ABSTRACTIsothermal electron beam heating has been combined with in situ optical measurements in order to measure the emissivity of coated silicon samples at elevated temperatures. The coatings include a number of oxide, nitride, and silicon films. Infrared emission spectra were recorded from I to 9 μm for temperatures between 750 and 1200°C. The experimental results were compared with calculated theoretical values, which were predicted from the theory of thin film coatings, using a matrix model incorporating the optical constants for the materials. A good match between experimental and theoretical values validates the use of the infrared optical constants for theoretical modelling related to control and temperature measurements in rapid thermal processing systems.

Surface roughening by electron beam heating

The effect of electron beam heating during the preparation of clean silicon surfaces suitable for epitaxial studies in ultrahigh vacuum conditions was investigated using surface chemical characterization techniques and transmission electron microscopy. The electron beam irradiation produced a disordered surface on the incident side of the sample and well-ordered monoatomic steps on the other surface, even at electron energies as low as 3 keV. These results have significant implications for epitaxial thin film growth.

Transmission Electron Miscroscopy Observation of the Decomposition of YBa2Cu4O8 into YBa2Cu3O7-δ and CuO

The decomposition of Yba2Cu4O8 (Y-124) into Yba2Cu3O7-δ (Y-123) and CuO at high temperatures has been expected to create Y-123 with finely dispersed CuO precipitates suitable for flux pinning. In fact, samples of thermally decomposed Y-124 exhibit a critical current density, Jc, which is enhanced with respect to the starting material as well as to pure Y-123. Transmission electron microscopy (TEM) studies of furnace annealed Y-124 were not suitable to clarify the reason for this Jc enhancement. Nevertheless, the formation and growth of CuO precipitates have been observed by in situ decomposition of the Y-124 starting material due to electron beam heating within the TEM.

Influence of MgO(1 0 0) substrate surfaces on epitaxial growth of Ti films

Abstract The growth of Ti films prepared on MgO(1 0 0) substrates by an electron-beam heating method has been studied using transmission electron microscopy. The 10 nm thick Ti films deposited on as air-cleaved chemically-polished MgO(1 0 0) substrates without heat treatment showed fcc electron diffraction spots due to TiHx crystallites (x ≒ 1.5) with NaCl structure and TiOy crystallites (y ≒ 1.0) with CaF2 structure, which were formed by compound layer containing H and O atoms, in addition to hcp Ti rings. When a 50 nm thick Ti was deposited at room temperature (RT) on chemically-polished MgO(1 0 0) substrates with heat treatment at 900°C for 30 min, hcp Ti crystallites with only (1 0 · 1) orientation were formed. The Ti films heat treated at 800°C for 30 min in vacuum after being deposited at RT indicated the existence of discrete and fully oriented hcp Ti crystallites. On the other hand, when a 50 nm thick Ti was deposited at RT on as air-cleaved ones without heat treatment, hcp Ti crystallites with only (0 0 · 1) orientation grew on most of the surface. This result shows that the epitaxial growth of Ti film is not necessarily inhibited by the exposure of MgO substrate surface to atmosphere, and that such surface is very effective for the growth of epitaxial films with preferred orientations.

Nonlinear Fracture Mechanics Analysis of Surface Crack Propagation in Fusion Reactor First Wall by Cyclic High Heat Flux Irradiation

Crack generation and propagation through the first wall of a fusion reactor under cyclic thermal stress caused by pulsed reactor operation has been studied analytically, and the results have been compared with experimentally acquired data. The analysis first covered the transient heat transfer through a test specimen pulse-heated on one face and constantly cooled on the reverse face. This was followed by elastoplastic stress analysis to estimate the stress-strain relation that prevails during pulsed heating. Finally, the crack propagation behavior was analyzed applying the non-linear fracture mechanics parameter termed “extended J-integral”, and calculated with the three-dimensional finite element code “MARC”. The results agreed well with experimental data obtained on a test specimen of type 316 stainless steel plate that was subjected to cyclic electron beam heating. This indicated the possibility of validly predicting the crack propagation behavior of a fusion reactor first wall.

Storage-ring free-electron-laser amplifiers and the microwave instability

We discuss the storage-ring longitudinal dynamics by including the contributions from a free-electron-laser amplifier and from the microwave instability. We show that the two effects exhibit a mutual interplay that leads, under certain conditions, to the inhibition of the start up of the microwave instability and/or to a reduction of the electron-beam heating due to the free-electron laser. The agreement with the experimental results is also discussed.

Fine-Scale Oscillatory Banding in Otoliths from Arctic Charr (Salvelinus Alpinus) and Pike (Esox Lucius)

AbstractTransmission electron microscopy of otoliths from the inner ear of arctic charr and pike has revealed the presence of fine banding on the scale of several nanometers. The thickness of the bands was observed to vary in different portions of the sample, and some areas were not banded. EDS analysis could not detect chemical differences within the bands, but electron diffraction showed that the crystallographic orientation of the bands is related by a lattice mismatch indicative of a twinning relationship. Previously, banding on the scale of 50 to 100 microns was observed by SEM in otoliths from arctic charr and was attributed to seasonal variations in growth. The fine-scale twinning observed in this study, however, is unlikely to be nucleated through daily variations. Electron diffraction from the pike samples shows that the material is composed of CaCO3 having the both the vaterite and aragonite structure, and hydrous CaCO3 was also observed.The interaction of the electron beam with the sample material was investigated by conducting several electron-irradiation experiments. The electron beam was observed to interact strongly with the sample and caused the precipitation of cubic CaO from the calcium carbonate matrix. Bright-field imaging showed the development of fine grained (∼ 5 nm) randomly-oriented crystallites which accumulated with increasing electron dose. These initial results suggest that the precipitation of GaO is not driven by electron-beam heating. Previously, a similar phase-change phenomenon has been observed in hydroxyapatite from dental enamel. Other Ca-bearing biominerals may therefore also be expected to be sensitive to electron irradiation.

Nonlinear Fracture Mechanics Analysis of Surface Crack Propagation in Fusion Reactor First Wall by Cyclic High Heat Flux Irradiation.

Crack generation and propagation through the first wall of a fusion reactor under cyclic thermal stress caused by pulsed reactor operation has been studied analytically, and the results have been compared with experimentally acquired data. The analysis first covered the transient heat transfer through a test specimen pulse-heated on one face and constantly cooled on the reverse face. This was followed by elastoplastic stress analysis to estimate the stress-strain relation that prevails during pulsed heating. Finally, the crack propagation behavior was analyzed applying the non-linear fracture mechanics parameter termed “extended J-integral”, and calculated with the three-dimensional finite element code “MARC”. The results agreed well with experimental data obtained on a test specimen of type 316 stainless steel plate that was subjected to cyclic electron beam heating. This indicated the possibility of validly predicting the crack propagation behavior of a fusion reactor first wall.

Infrared Emission Spectra of Indium Phosphide at Elevated Temperatures

ABSTRACTProcess monitoring and control during semiconductor device fabrication frequently relies on good knowledge of the optical properties of the substrate wafer and the surface coatings. However, these optical data are often unavailable, and as a consequence errors arise in pyrometric temperature measurements, as well as in thermal modelling of heating cycles. In this study, isothermal electron beam heating has been combined with in situ optical measurements to record thermal emission spectra of undoped InP specimens from 347 to 478°C, at wavelengths between I and 9 μm. The absorption coefficient was deduced from the emission spectra and reveals information about the temperature dependence of the infrared absorption mechanisms in InP.

Surface Morphologies and Magnetic Properties of Fe Thin Films with Underlayers.

Fe thin films with underlayers of various materials were continuously prepared by the evaporation method with an electron beam heating equipment on glass substrates at room temperature. The film thickness dependence of the saturation magnetization Is and of the coercive force Hc of double-layered Fe/(Ag, Cu, Bi, or Si) films was measured. The largest value of saturation magnetization Is among the double-layered films was 20 kG, for an underlayer material of Ag with a thickness of 50.0 nm, and was larger than that of Fe thin films deposited directly on glass substrates. The compositions and the surface morphologies of an Fe/Ag double-layered film were also investigated by measuring the AES spectra and the AFM images, respectively. These results indicate that the surface morphology of Fe thin film with underlayer is closely related to the magnetic properties.

Regrowth of amorphous regions in semiconductors by sub-threshold electron beams

Spatially isolated amorphous zones produced in Si, Ge and Gal' by low energy, low dose ion implantations can be regrown at room temperature by using an electron beam to stimulate the process. The rate at which these zones regrow is dependent on the energy of the electron beam and on the size of the amorphous zone produced by the implant. In the three materials, the rate of regrowth decreases as the energy of the electron beam increases from 25 keV reaching a minimum below the threshold displacement energy. The rate then increases as the energy of the electron beam increases. Electron beam heating effects have been calculated and shown to be insignificant. To account for these observations, the possible role of defects in the amorphous and crystalline material migrating to the amorphous—crystalline interface, and of defects at the amorphous-crystalline interface in causing regrowth are considered.

Infrared absorption in silicon at elevated temperatures

Isothermal electron beam heating combined with in situ optical measurements has been used to measure the temperature dependence of the spectral emissivity of lightly doped silicon in the range 345–723 °C for wavelengths between 1 and 9 μm. The absorption coefficient was deduced from the spectral emissivity and compared with the predictions of a model including phonon-assisted processes involved in interband transitions, free-carrier absorption, and lattice absorption. The experimental data agree well with the model’s results.

New electron beam facility for irradiated plasma facing materials testing in hot cell

Since plasma facing components such as the first wall and the divertor for the next step fusion reactors are exposed to high heat loads and high energy neutron flux generated by the plasma, it is urgent to develop plasma facing components which can resist these. We have established electron beam heat facility (‘OHBIS’, Oarai hot-cell electron beam irradiating system) at a hot cell in JMTR (Japan materials testing reactor) hot laboratory in order to estimate thermal shock resistivity of plasma facing materials and heat removal capabilities of divertor elements under steady state heating. In this facility, irradiated plasma facing materials (beryllium, carbon based materials and so on) and divertor elements can be treated. This facility consists of an electron beam unit with the maximum beam power of 50 kW and the vacuum vessel. The acceleration voltage and the maximum beam current are 30 kV (constant) and 1.7 A, respectively. The loading time of the electron beam is more than 0.1 ms. The shape of vacuum vessel is cylindrical, and the main dimensions are 500 mm in inside diameter, 1000 mm in height. The ultimate vacuum of this vessel is 1 × 10 −4 Pa. At present, the facility for the thermal shock test has been established in a hot cell. The performance of the electron beam is being evaluated at this time. In the future, the equipment for conducting static heat loadings will be incorporated into the facility.

A15 type structure of ultrafine chromium particles studied by UHV-HRTEM

We found that ultrafine chromium (Cr) particles prepared in UHV condition have an A15 type structure different from their bulk crystals by UHV high-resolution transmission electron microscopy (JEM 2000FXV). Cr (99.999% purity) was evaporated in situ in the UHV microscope by electron beam heating to various diameters ranging from 5 to 20 nm onto an amorphous carbon substrate kept at 600°C. Diffraction patterns of the Cr particles showed the (200), (210) and (211) spots expected from the A15 type structure, while they showed no diffraction spots from the bcc structure. From the high-resolution images of the Cr particles, showing the (110), (111), (200) and (220) lattice fringes of the A15 type structure, we confirmed that the stable phase of the clean ultrafine Cr particles has an A15 type structure.

An experimental and numerical investigation of post-CHF heat transfer for one-sided heat load with highly sub-cooled flow boiling

Abstract One-sided high heat fluxes are very commonly found in fusion reactor plasma facing components for proposed long-pulse devices, such as ITER. Heat fluxes between 5 and 30 MW m −2 are removed by a highly sub-cooled flow of boiling water. For one-sided heat loads, all boiling regimes (single-phase, nucleate, fully developed sub-cooled, transition and film boiling) can be present under a stable condition which, in certain cases, can exceed the local critical heat flux (CHF) value. A thorough numerical and experimental analysis of the post-CHF phenomenon under a one-sided heat load has been carried out. The entire boiling curve was described with available correlations for all the regimes, except for the transition regime, where an assumed path was used. Numerical results for a circular channel under a non-uniform, one-sided heat load showed stable post-CHF temperature distributions. The sensitivity of the numerical analysis to the assumed transition boiling region was studied. During electron beam heating experiments, temperature distributions in a circular channel and a diverter plate (DP) were measured, and the ultimate load (“burnout”) was observed in circular channels with and without twisted tapes. The enhancement of the ultimate heat flux over the local CHF value was found to be 2 for a DP and 1.5 for a round channel. It was shown that the enhancement factor η is highly dependent on the wall thickness and flow parameters. Good agreement was found when the numerical results for the temperature distributions were compared with the experimental data. An increase of about 100% in the burnout heat flux was observed in circular channels with a twisted tape. The overall results show that safety margins in actively cooled plasma facing components can be increased when conditions for stable post-CHF exist.

Separating thermal, electronic, and topographic effects in pulsed laser melting and sputtering of gold.

An attempt was made to separate thermal from electronic effects during laser sputtering of gold by partitioning the target surface energy between steady-state electron beam heating and pulsed laser heating. For flat starting surfaces and a peak surface temperature of $\ensuremath{\sim}2700\mathrm{K}$, the Au translational energy remains $(2\ensuremath{-}3)\ifmmode\times\else\texttimes\fi{}$ higher than classical expectations and is insensitive to how energy is partitioned between steady-state heating and laser heating. The mean desorption energy is linearly dependent on peak surface temperature, but with a slope of ${15k}_{B}T$ as opposed to the classical ${2k}_{B}T$.

CRITICAL GRAIN SIZE FOR STRUCTURAL TRANSFORMATION IN VACUUM-DEPOSITED MOLYBDENUM FILMS

Nanometer-grained polycrystalline films were prepared by vacuum deposition of molybdenum (Mo) by using electron-beam heating. The structure and composition of the grains were analyzed by high-resolution electron microscopy and Auger electron spectroscopy, respectively. The concentration of carbon in the films was measured in relation to reduction of the grain size to nanometer scale. The grains had a bcc structure when the grain size was larger than 4 nm. On the other hand, the grains smaller than 4 nm for films had a fcc structure. Large amount of carbon was included in the grains with the fcc structure in comparison with the grains of bcc structure, although amount of other impurities such as nitrogen and oxygen was similar in both grains. It was found that the structure was transformed from bcc to fcc below the critical grain size, 4 nm, and the grains with the fcc structure were cubic Mo-C.