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The Dielectric Barrier Discharge (DBD) is composed of
many Filamentary Discharges (FDs), and it can be applied to ozone
generation, gaseous pollution control, etc. In our laboratory, we
investigated efficient cleaning methods of diesel exhaust gas by DBD. From
the results of numerical simulation of chemical reactions, a homogeneous DBD
was expected to improve the efficiency of pollution control and also the
ozone yield. Recently, we found that a DBD device using alumina as barrier
material can generate an Atmospheric Pressure Townsend Discharge (APTD) in
air. In this research, we setup two ozonizers with different discharge modes
of FD and APTD, and compared the ozone yield. The experimental results
showed that the ozone yield was higher by the FD mode than by the APTD mode
in lower Specific Input Energy (SIE) region. However in the region that the
SIE is larger than 420J/L, the APTD mode showed higher ozone yield than FD
A novel method to develop new quaternary alloys with an fcc/L12 coherent structure is proposed. This paper reviews the development of quaternary Ir-Nb-Ni-Al alloys. The microstructure, lattice misfit, and compressive 0.2% flow stress of 15 kinds of alloys were investigated systematically. Two kinds of coherent structures, fcc/L12-Ir3Nb and fcc/ L12-Ni3Al, were observed in most alloys. Two two-phase structures, fcc+L12-Ir3Nb and fcc+L12-Ni3Al, were observed in Ir-rich and Ni-rich regions, respectively. The lattice misfits of quaternary Ir-Nb-Ni-Al alloys were higher than those of Ni- or Ir-base binary alloys. The compressive 0.2% flow stresses of quaternary alloys increased dramatically compared with those of Ni-base superalloys. The quaternary alloys located in the Ir-rich region were not only had higher strength but also better ductility than Ir-base binary alloys. The potential use of quaternary alloys is discussed.
Two types of shape and contrast features of superconducting vortices in a Lorentz micrograph were obtained by the newly developed 1-MV field-emission transmission electron microscope on a Bi2Sr2CaCu2O8+8(Bi-2212) thin specimen containing tilted columnar defects. The shape and contrast features could be consistently interpreted by the simulation that some vortices were pinned along tilted columnar defects and others were unpinned. The interesting property for temperature change of vortex core inside the material was also observed.
A single crystalline Bi2Sr2CaCu2O8+8 which has columnar defects in its inside are observed by Lorentz microscopy using the newly developed 1-MV field emission electron microscope at the first time. The superconducting vortices are observed with higher contrast than ever. Simultaneous observation of vortices and columnar defect is succeeded in real time.
Higher crystalline Si volume fractions in hydrogenated microcrystalline silicon ( µc-Si:H) films have been achieved by the hot-wire assisted plasma enhanced chemical vapor deposition (HWA-PECVD) method compared with those in films by conventional PECVD. µc-Si:H films can also be prepared by HWA-PECVD under typical conditions used for preparing hydrogenated amorphous silicon (a-Si:H) films by PECVD, in which the hydrogen-dilution ratio (H2 / SiH4) is ∼ 10. The hot wire seems to produce hydrogen radicals. As a result, the HWA- PECVD method can control hydrogen-radical densities in the RF plasma, and this method can also control the ratio of hydrogen coverage at the surface of the film.
Hydrogenated microcrystalline silicon (μc-Si:H) films are prepared by hot-wire assisted plasma enhanced chemical vapor deposition, which controls the hydrogen radical density by filament temperatures, Tf, without changing other conditions. The effect of hydrogen radical on the properties of incorporated hydrogen into μc-Si:H films is studied using infrared absorption and gas effusion spectroscopies. The hydrogen concentration decreases with increasing Tf. The crystalline volume fraction, Xc, increases with Tf and shows a peak at Tf of 1850 °C. Integrated intensities of the modes near 2000 and 2100 cm-1 decrease with increasing Tf. Integrated intensity of the mode near 880 cm-1 shows almost same tendency of Xc. The effect of hydrogen radical on the properties of incorporated hydrogen into μc-Si:H films is discussed.
Nitrogen atoms exist in silicon as non-reactive nitrogen molecules. This is concluded from two I-R absorption experiments: one is the nitrogen isotope effects on N- N pairs and the other is silicon isotope shifts at 10 K. Intrinsic resistivities (over 20 K ohm-cm) are obtained by annealing at 1000°C, 1 min. in N2 in both p- and n-type nitrogen doped thin wafers. Resistivity increases are due to deep- level generations: 0.66 eV above the valence band for p-type and mainly 0.44 eV below the conduction band for n-type material. These deep levels are considered to be formed by nitrogen pairs and divacancies which are incorporated during growth. Since divacancies are easy to out diffuse to the wafers surface, the deep levels are also irreversibly removed. Diffusion coefficient of Si intersititialswici'ch are annihilated with divacancies in the lattice are calculated as 6×10−6cm2/s and 2×10−6cm2/s at 900°C and 1000°C respectively. Migration energy of Si interstitials is about 4.5 eV.
Infrared absorption measurements have been made in three kinds of Bi compounds of a high-Tc family mainly by making use of powdered samples. Two of them are superconductors with Tc's of 108 K and 82 K, respectively, and the remaining one is a semiconductor. In each of the superconducting compounds, there appears Mid-Infrared absorption band: No such absorption band is found in the semiconducting compound. At Far-Infrared region, many absorption peaks due to phonons are clearly detected in all of these samples. Some of the phonon modes have been identified. At very low energy region, free carrier absorption appears in superconductors. Only this part of the absorption shows a temperature dependence. Absorption intensity decreases as the temperature decreases.
The concentration and arrangement of Si vacancy in aluminum or phosphorus containing ReSi1.75 based silicides have been investigated. Both aluminum and phosphorus are substituted with silicon. In addition to the (001)C11b twins usually observed in binary ReSi1.75, planar defects are heterogeneously formed in both of the silicon substituted ternary alloys with small amount. By using the high resolution electron micrograph (HREM) technique, the planar defects are assigned as crystallographic shear (CS) planes lying on (109) C11b and (107) C11b in aluminum and phosphorus containing ReSi1.75, respectively. The CS vector in both ternary alloys is C11b. Since the concentration of vacancies in the ReSi1.75 structure is changed by the introduction of these crystallographic shear, ternary alloys with silicon substituted by aluminum and phosphorus contain more or less amount of vacancies than the binary alloy, respectively. This implies us that concentration of Si vacancies changes so as to retain the average number of valence electron. We can control the concentration of Si vacancy in the ReSi1.75 based alloys.
The reaction between Al and CVD-W films has been studied. Al/α-W/Si and Al/β-W/Si structures were prepared by deposition on different Si substrates by changing deposition conditions using silane reduction of tungsten hexafluoride, followed by Al-Si-Cu alloy film sputter deposition. The sheet resistance of Al/α-W/Si structure is higher than that of Al/β-W/Si structure after 500°C annealing. RBS measurements show that the W diffusion into Al occurs in both structures after annealing, and the reaction between α-W and Al takes place easily compared with that between β-W and Al. This causes the sheet resistance difference. The activation energies for the W diffusion into Al, however, are almost the same in both structures. When CVD-W films are exposed to air after removal from the reactor, the sheet resistance of β-W film increases according to the exposure time, while that of α-W film does not. AES measurements indicate that the β-W film absorbs more oxygen than the α-W because of the difference of grain structures. The resistance increase of β-W film is caused by the oxygen that is absorbed from air. Our results indicate that the oxygen in the β-W layer suppresses the W diffusion into Al. Once the reaction begins, however, the diffusion into Al does not depend on crystalline phases of CVD-W.
Hg (mercury) in GaAs is known to be a moderately deep acceptor impurity, having a 52 meV activation energy. Optical properties of Hg acceptors in GaAs were systematically investigated as a function of Hg concentration, [Hg]. Samples were prepared by high-energy ion-implantation of Hg+ into GaAs grown by the liquid encapsulated Czochralski (LEC) method. Heat treatment was made by furnace annealing and rapid thermal annealing. Photoluminescence measurements at 2K revealed that the Hg-related so-called “g” line is formed in addition to the well-defined conduction band-to-Hg acceptor transition, (e, Hg). Additionally, three shallow emissions are formed for net hole concentrations INA-NDI greater than 2×1017cm−3 . This is the first demonstration that even Hg in GaAs makes multiple shallow emissions due to acceptor-acceptor pairs and LEC GaAs can be used for the investigations of these emissions.
Magnetic lines of force penetrating a superconducting thin foil have been investigated by means of electron holography. A field-emission TEM with a specially constructed cold stage was used to cool a Nb thin foil down to 4.5 K and apply magnetic fields up to 100 G. The specimen is tilted by 45° to both the electron beam and the magnetic field (applied horizontally) allowing the 2-D lattice of penetrating flux-lines to be discerned. The phase distribution of electrons transmitted through the specimen were quantitatively measured. Interference micrographs revealed tiny regions where the phase distribution rapidly changed. These regions coincided spatially with the spot-like contrast observed by Lorentz microscopy and were found to be quantized vortices containing a flux of h/2e. The experimental results were in good agreement with those predicted by theoretical simulations. Experiments exploring the vortex inner core structure at high resolution are presented.
In dislocated Cz-Si crystals, rows of flow patterns (FP) and Secco etch pits (SEP) (2–3 mm in length, along <110> direction) can be revealed by Secco etch without agitation. In this study, the crystal defects forming FP-SEP rows in dislocated Cz-Si crystals are investigated by transmission electron microscopy. Microdefects, 0.1 μm in size, are observed in a row along a FP-SEP row, <110> direction. These defects were identified as oxygen precipitates with or without dislocation loops (interstitial-type), and voids with oxidized interiors. We conclude that FP originate from interstitial-type dislocation loops, and SEP are due to oxygen precipitates or voids.
Ir- and Rh-base refractory superalloys with an fee and Lb two phase structure similar to Ni-base superalloys, yet with considerably higher melting temperatures have been proposed. Fee and Ll2 two phases were observed in these alloys by transmission electron microscopy and X-ray powder diffractometry. The compression tests of these alloys showed that the strengths of several alloys were about 200 MPa at 1800 °C and these alloys have potential to become ultra-high temperature materials for use in power engineering field.
Point defect properties have been studied for B2-type Co1-cFec alloys (0.4 ≤ c ≤ 0.6 ) by X-ray diffraction and density measurements. The lattice constant increases with increase in composition c and indicates a distinct change in the slope beyond c = 0.5. Further, it shows a decrease with increase in quenching temperature. The obtained vacancy concentration is very low for any composition and temperature concerned. Thus, it can be concluded that defect type in B2 CoFe is an antisite atom. The change in the lattice constant with quenching temperature can be related to the long-range order (LRO): it is well approximated by a linear form with respect to square of the LRO parameter. CoFe alloys in both B2 and higher temperature A2 phase regions show ferromagnetism. Observed results are discussed taking a correlation between the defect structure and the magnetic behavior into account.