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The macro and micro morphology of the Si surface, depending on noble metal ion concentration in etching solution, prepared by metal assisted etching were investigated. We defined the morphology of etched Si in four types, and developed the phase diagram of Si morphology. Mixture of silver nitrate (AgNO3) and hydrofluoric acid (HF) was used as an electroless-plating bath of Ag, as well as etching solution of Si. The morphology of the etched Si surface as function of concentration of AgNO3 in etching solution was observed by SEM. With increasing concentration of the AgNO3 in the etching solution, the surface of etched Si tended to be porous structure with very fine pores of a few nm (porous Si). When concentration of AgNO3is low, single crystal Si nanowires with a smooth surface without pores were observed.
Bi2223 multifilamentary tapes with enhanced transverse resistivity by introducing Ca2CuO3 and SrZrO3 as interfilamentary barriers were prepared and their AC loss properties were examined under AC external magnetic field. To improve the deformation properties of these oxide powders, 20-30wt% Bi2212 powders were mixed with them. The mixed oxide powders were introduced among the twisted Bi2223 filaments by using dip-coating method. AC loss properties under AC parallel or perpendicular field were measured and compared with the results for the tape without barriers. The loss measurements were carried out by changing both the amplitude and the frequency of external field. Based on the experimental results, the effect of barrier introduction on the loss reductions was discussed.
Incorporation of Si ion implantation to GaN metal semiconductor field effect transistor (MESFET) processing has been demonstrated. The channel and source/drain regions formed using Si ion implantation into undoped GaN on sapphire substrate. In comparison with the conventional devices without ion implanted source/drain structures, the ion implanted devices showed excellent device performance. On-state resistance reduces from 210 Ω-mm to 105 Ω-mm. Saturation drain current and maximum transconductance increase from 36 mA/mm to 78 mA/mm and from 3.8 mS/mm to 10 mS/mm, respectively.
Ti/Al ohmic contact with an extremely low specific contact resistance has been formed by the deposition of Ti and Al films on Si+ lanted GaN. The ohmic contact formed by annealing at 600 o C of Ti film with a thickness of 50 nm and Al film with a thickness of 200 nm reveals the good smooth surface and uniform structure as compare to those of contacts formed above 700 °C, which is correlated to whether the Al-Ti alloy is melted during the annealing of ohmic contact or not. The specific contact resistance of 2 × 10-6Ω-cm2 is obtained for Si+ implanted GaN with a dose of 5 × 1013 cm-2. As Si ion dose increases to 5 × 1014 /cm2, the specific contact resistance is reduced to 2 × 10-8 Ω-cm2. It is revealed that the selective doping at high impurity concentration in the surface region by Si+ implantation is useful to reduce the contact resistance for Ti/Al contact to GaN.
The influence of lateral critical current density (Jc) distributions on AC transport losses in self-fields at 77 K have been investigated on the Ag-sheathed (Bi, Pb)-2223 multifilamentary tapes with different filament arrangements. The trapped magnetic field distributions in a remanent state on the tape surface measured by a scanning Hall sensor depend on the filament arrangements and gradually deviate from the calculation results of magnetic profile without any Jc variations in their cross sections. The transport loss values are strongly influenced from the filament arrangements in each tape, although the main contribution to the losses comes by the hysteresis loss in the superconductor. These results are explained by the calculation results of the shape of field-free core and flux-penetration-regions, varying with filament arrangements and local Jc distributions along a width direction.
In 1996, three adenovirus type 7 (Ad7) strains were isolated from children with fever and
upper respiratory diseases in Japan. Restriction endonucleases (REs) analysis and PCR
amplification of the E3 7·7 kDa ORF revealed that these strains were genotype Ad7h and
closely related to an Argentine Ad7h strain, which has been reported to be highly virulent and
so far predominant only in South America. These strains showed weak cross-neutralizing
activity and specific haemagglutination-inhibition activity to Ad3 antiserum. The present
findings suggest that Ad7h in South America has spread to other parts of the world. Since the
seroprevalence to Ad7 in the current Japanese population is very low due to the absence of
Ad7 circulation in Japan for decades, Ad7 outbreak as a typical case of re-emerging infectious
diseases is a cause for serious concern.
Oxygenation characteristics in high-density YBa2Cu3Ox ceramics with a relative sintered density ≥97%, which were produced by hot-pressing to have various oxygen contents as-hot-pressed, have been investigated. The results indicate that the oxygenation characteristic in the materials was strongly affected by their oxygen content before oxygenation; that is, the attainable oxygen content (directly connected with the superconducting temperature Tc) of the materials after oxygenation increases with a decrease in their oxygen content before oxygenation. Oxygen annealing at 500 °C for 24 h dramatically increased the oxygen content of an YBa2Cu3Ox with x = 6.08 before the oxygen annealing up to 6.90, while the oxygen content of an YBa2Cu3Ox ceramic with x = 6.32 before oxygenation rose only to a value of 6.61 after the same oxygen annealing. This newly observed phenomenon on the oxygenation characteristic in the present materials may provide an idea for improving the superconducting properties in high-density YBa2Cu3Ox ceramics.
Improvements of crystal quality in GaAs/Si heterostructure by solid phase epitaxy (SPE) are described. RBS and TEM measurements indicate that high density defects are located near the GaAs/Si interface after “2-step MBE”. Utilization of post SPE process (amorphization plus regrowth) significantly improve crystal qujali ty at the GaAs/Si interface, although a small stress field is introduced. In addition a new relation between photoluminecence intensity ratio and stress field is established. This provides a useful too] for measuring small stresses remaining in the GaAs/Si hetero-structure.
Rapid thermal annealing by using a graphite strip heater has been employed to activate Se atoms implanted in either In-doped or undoped LEC GaAs. Doping profile measurements have shown that highly doped n-type layers with the maximum carrier concentration of 1.2E19/cm3 are formed in the In-doped GaAs implanted with 100keV Se ions at room temperature after rapid thermal annealing at 1000°C for 10 sec. Residual defects existing in Se-implanted layers have been examined. The results show that the introduction of dislocations into Se-implanted layers during post-implant annealing is minimized in the In-doped GaAs samples treated by rapid thermal annealing.
Epitaxial NiSi2 layers have been grown onto (100) and (111) Si substrates by multiple scan electron beam annealing. The formation and the composition of the silicides have been analyzed by Rutherford backscattering techniques and by electron diffractionobservation. The phase and the composition of the silicides depend on the power density of the electron beam. Under the optimum conditions, epitaxial NiSi2 layers with a high surface morphology can be grown. An attempt has been made to form crystalline Si—NiSi2—Si heterostructures and the preliminary data are also presented.
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