Shigeki Tsukui

Nanoparticle Formation Mechanism in CVD Reactor with Ionization of Source Vapor

A new chemical vapor deposition (CVD) method, called ionization CVD, was developed, to produce non-agglomerated nanoparticles in which reactant gases are charged. A sonic-jet corona discharger was used as an ionizer in the developed nanoparticle generator. For a tetraethylorthosilicate (TEOS)/O2 chemical system, SiO2 nanoparticles were prepared. All particles formed by the ionization CVD were charged unipolarly. SEM micrographs of particles showed that the repulsive Coulombic force between charged particles reduces their coagulation rate and produces non-agglomerated nanoparticles that have a relatively high number concentration and small size. An external field was used to collect the charged particles onto Si wafers. These collected samples indicated that the deposition of charged particles could be controlled by the external electric field. Particle concentration measurement with a condensation nucleus counter at various TEOS concentrations suggested the particle formation mechanism in the ionization CVD was an ion-induced nucleation.

Gamma-ray irradiation effect on corrosion rates of stainless steel, Ti and Ti-5Ta in boiling 9N nitric acid

Abstract Irradiation effect of γ-rays on corrosion rates of stainless steel (type 304L), titanium and a titanium-tantalum alloy (Ti-5Ta) in 9N boiling nitric acid was investigated by measuring weight losses of specimens leached under a 60 Co γ-ray environment of 1 kCkg −1 /h (4 MR/h). Tests without irradiation were as well performed to obtain reference data. Plots of the weight loss normalized to specimens surface area against total leaching time exhibited linear relations when the first leaching batch is neglected. The corrosion rates calculated from the gradients indicated slight, though significant, irradiation effects, an enhancement in stainless steel while suppressions in Ti and Ti-5Ta. Corrosion modes were found to be insensitive to the irradiation.

Fabrication of YMnO3 thin films on Si substrates by a pulsed laser deposition method

We have proposed ReMnO3 (Re: Rare earth elements) films for metal-ferroelectric-semiconductor field effect transistor-(MFSFET) type ferroelectric random access memories (Ferroelectric RAMs). For this kind of application, since ReMnO3 films must be fabricated directly on Si substrates, this wrote focuses on the fabrication of YMnO3 films on Si substrates with and without buffer layers. Although only amorphous YMnO3 films are obtained without buffer layers, crystalline films are obtained using Y–Mn–O buffer layers deposited without introducing oxygen. YMnO3 films can be epitaxially grown on the top of epitaxial Y2O3 on (111)Si. For both crystalline YMnO3 films, although hysteresis behavior in D-E measurement is observed, remanent polarizations are quite small. The role of buffer layers on the thin film growth of YMnO3 on (111)Si is discussed.

Ion-Induced Nucleation in Nanoparticle Synthesis by Ionization Chemical Vapor Deposition

Particle formation mechanisms in nanoparticle synthesis by ionization chemical vapor deposition (CVD), in which source gases are ionized before being fed into the reactor, were investigated experimentally. First, nonagglomerated nanoparticles were formed from a tetraethylorthosilicate (TEOS)/O 2 mixture ionized with a sonic-jet ionizer at various furnace temperatures, T f, and TEOS concentrations, N TEOS. Then, the electrical mobility of the nanoparticles and ions were measured using a differential mobility analyzer combined with a Faraday cup electrometer, and the particle number concentration by a condensation nucleus counter. Measurements at 293 ≤ T f ≤ 1173 K and 0 ≤ N TEOS ≤ 1.38 × 10 −5 mol/l showed that (a) negative TEOS and TEOS cluster ions were formed at T f = 293 K, (b) gas-phase intermediates forming nanoparticles were formed at T f ≥ 673 K, (c) for T f = 873 K condensation of the intermediates onto ions (i.e., ion-induced nucleation) started at N TEOS ≥ 4.48 × 10 −7 mol/l, and (d) the growth from ions to nanoparticles was discontinuous for this change in N TEOS.

Nanoparticle Synthesis by Ionizing Source Gas in Chemical Vapor Deposition

A new chemical vapor deposition (CVD) method called ionization CVD, in which reactant gases are ionized, was developed for the synthesis of nanoparticles. In such a CVD method, the particles formed are charged and the repulsive Coulombic force between them suppresses their coagulation, producing non-agglomerated particles that have a relatively high number concentration and small size. A tetraethylorthosilicate (TEOS)/O2 mixture was ionized by using a sonic-jet corona discharger. All particles formed by the ionization CVD had a negative charge and their sizes and number concentrations were 1/6–1/15 times smaller and 10–150 times higher, respectively, than those of particles formed by conventional CVD. The mean diameter of the smallest particles prepared with ionization was 8.9 nm.

Direct Observation of 18O Tracer Diffusion in a YBa2Cu3Oy Single Crystal by Secondary Ion Mass Spectrometry

Direct observation of 18O tracer diffusion by secondary ion mass spectrometry (SIMS) was made on a single crystal of YBa2Cu3Oy with an array of steps on the stairlike surface. The unique distribution of the diffused 18O in the ab-plane and in the c-axis direction was shown visually as a mapped image, which revealed some fundamental processes on the oxygen penetration through the surface and diffusion in the inner crystal. It was found that at 530°C, the diffusion coefficient in an ab-plane is larger than that in a c-axis direction by more than five orders of magnitude.

Fabrication of Y2O3-Doped Zirconia/Gadolinia-Doped Ceria Bilayer Electrolyte Thin Film SOFC Cells of SOFCs by Single-Pulsed Laser Deposition Processing

An 8 -mol. % Y2O3-doped zirconia/10-mol. % GdO2-doped ceria (YSZ/GDC) bilayer electrolyte and a Gd0.5Sr0.5CoO3 (GSCO) cathode were deposited by a single-processing, pulsed laser deposition (PLD) method to fabricate anode support cells. No additional heat treatment was needed. Laser frequencies of 10, 20, and 100 Hz were used to deposit bilayer electrolytes between the NiO–YSZ (NiO:YSZ = 60:40 wt. %) anode substrate and the GSCO cathode thin film. The GDC thin film produced at 10 Hz was smooth, well-crystallized, and highly dense. The crystallinity of the GSCO cathode on the GDC was also improved. We concluded the GDC crystallinity affected the crystallinity of the cathode thin film. The resistivity of the YSZ single layer (5.7 μm thickness) was 1.4 times higher than that of the YSZ/GDC bilayer (YSZ 3.0 μm thickness, GDC 2.7 μm thickness) at 600 °C and that of the YSZ-GDC interface became low. The optimum YSZ thickness was found to be approximately 3.0 μm, at which thickness there was effective blocking of the passage of hydrogen molecules and electrons. A cell with a YSZ (3.0 μm thickness, fabricated at 20 Hz)/GDC (5.0 μm thickness, fabricated at 10 Hz) bilayer and GSCO cathode thin film exhibited a maximum power density of 400 mW·cm–2 at a comparatively low temperature of 600 °C.

Oxygen tracer diffusion in the YBa2Cu3Oy superconductor

Abstract The oxygen diffusion coefficient of YBa 2 Cu 3 O y (YBCO) single crystals was determined by secondary ion mass spectrometry in a wide temperature range from 628 to 1073 K. It was found that the slope of the Arrhenius plot of the diffusion coefficient changes at the transition temperature from the orthorhombic to the tetragonal phase (TP). The activation energies of oxygen in the TP and the orthorhombic phase (OP) are 89.1±1.4 and 114.6±1 kJ mol −1 in the ab plane, and 284±2.8 and 126.9±0.5 kJ mol −1 in the c axis direction, respectively. In the OP, the activation energies in the ab plane and the c axis direction are almost the same, but the diffusion coefficients in the ab plane are larger than that in the c axis direction by more than three orders of magnitude. At higher temperatures of the TP, the slope of the Arrhenius plot in the c axis direction becomes larger and the diffusion coefficient of the c axis becomes closer to that of the ab plane towards the incongruent melting point of YBCO compounds.

Superconductivity in Bi-2212 thin films of Bi2Ln0.3Ca2.7Cu2Oz (Ln=Pr, Nd, Sm, Eu and Gd) prepared by laser ablation method

Abstract The Bi-2212 thin films of the Bi2Ln0.3Ca2.7Cu2Oz system (Ln=Pr, Nd, Sm, Eu and Gd) have been prepared by the laser ablation method. The films are of metastable Bi-2212 phase, which has not been synthesized by the solid state reaction method. The highest zero resistivity temperature (Tcz) of 57 K has been found for the film with Ln=Pr, and the valence of Pr determined by XPS measurement was trivalent. Further, each of the films with various Ln elements had a Tcz value higher by 12–45 K than the corresponding sample of the bulk Bi2Ln0.5Ca2.5Cu2Oz system.

Superconductivity in Bi-2212 thin films of Bi2LaxCa3−xCu2Oz prepared by laser ablation method

Abstract We have synthesized Bi-2212 thin films of Bi 2 La x Ca 3− x Cu 2 O z with the composition range of 0.2≤ x ≤0.7 by the laser ablation method. Bi-2212 samples with the same range of composition have not been obtained by solid state reaction except the sample with x =0.5. The film with x =0.2 showed the highest starting temperature of diamagnetic signal ( T cm ) at about 78 K, and it changed from superconductor to insulator with increasing La content x .