Osamu Kido

Structure and optical spectrum of ZnO nanoparticles produced in RF plasma

ZnO particles were produced by dropping Zn powder into a heated boat just below the plasma electrodes in a mixture gas of argon and oxygen. The resulting particles look spherical with the size of 30 nm and were of tetrapod configuration having four [0 0 0 1] axes of ZnO. The dispersion became better than that in the case of another method without plasma. The ultraviolet-visible light transmittance of the specimen showed sharp absorption. The electric charge in the plasma field controlled the coalescence growth of each particle and improved the dispersion of the particles due to the plasma effect.

Structure and thickness of natural oxide layer on ultrafine particle

Ultrafine particles of various metals [Cr, Mn, Fe, Al, Ni, Cu, In, Si, Ge, Zn, Mg and Sn], produced by the gas evaporation method were covered with the oxide layer of thickness less than 10 nm by exposure to air. In order to clarify the structure and thickness of the surface oxide layer on various metal ultrafine particles, high-resolution electron microscopy and infrared spectroscopy have been extensively used.

Fabrication of an amorphous carbon tube from copper oxide whisker

The reduction process of tenorite whiskers grown on a copper mesh by heating in vacuum has been directly observed using a transmission electron microscope equipped with a real-time video-recording system. The coating of the carbon layer and reduction of the tenorite whisker covered with a carbon layer have also been captured in real time on video images. The growth process of an amorphous carbon tube has been elucidated.

Growth process of TiC clusters from Ti nanoparticles with evaporated carbon layer

Abstract Titanium carbide formation by the solid–solid reaction on the surface of Ti nanoparticles was studied in situ using a high-resolution transmission electron microscope with a heating stage. The cross-sectional image of the Ti surface was clearly observed. Vacuum-deposited carbon covered the whole the surface of Ti nanoparticles in spite of the partly evaporation on the nanoparticle surface. The diffusion of the carbon atoms inside the Ti nanoparticles depended on the size of the nanoparticles. When the Ti nanoparticle diameter was less than 30 nm, carbon atoms diffused into the Ti nanoparticle and formed TiC. The superstructure of the Ti nanoparticles was observed, which revealed the growth process of TiC to be the diffusion of carbon atoms. For Ti nanoparticles with diameter larger than 30 nm it was observed that diffusion of Ti atoms into the carbon layer was dominant, which resulted in formation of TiC in the carbon layer at the surface of Ti nanoparticles.

Phase transition temperature of γ-Fe2O3 ultrafine particle

The iron oxide ultrafine particles prepared by the gas evaporation method, in which commercial α-Fe 2 O 3 powder is evaporated, are composed of α-Fe 2 O 3 particles covered with a γ-Fe 2 O 3 mantle layer. To study the phase transition temperature of the γ-Fe 2 O 3 mantle layer, the particles were heated and observed in a transmission electron microscope. The present specimen of γ-Fe 2 O 3 transformed completely to α-Fe 2 O 3 at above 700°C, and this phase transition was irreversible. The phase transition temperature was 1.4 times higher than the bulk value. The growth mechanism of the present specimen of α-Fe 2 O 3 particles covered with the γ-Fe 2 O 3 mantle layer has been discussed in terms of the difference in the cooling rates between the inside and the surface of the particle at around the evaporation source.

Analysis of Mechanism of Improvement in Highly Accelerated Lifetime via Measurement of Vanadium Valence in Multilayer Ceramic Capacitors

The valence of vanadium was measured by electron paramagnetic resonance in order to explain the decrease in insulation resistance (IR) and the improvement in highly accelerated lifetime that resulted from the addition of vanadium. V4+ was detected in specimens with vanadium contents of 0.20 and 0.30 mol %, while no V4+ was detected in a specimen with a vanadium content of 0.06 mol %. It was also revealed that the content of the vanadium except for V4+ are the main factor responsible for the decrease in IR and the improvement in lifetime. The impedance of BaTiO3-based materials in multilayer ceramic capacitors with various vanadium contents was investigated in order to determine the mechanism of improving the highly accelerated lifetime using a four resistance and capacitor section electrical equivalent circuit. All four resistance components (R components) decreased with an increase in vanadium content. During the lifetime test, all four R components were degraded. In particular, the R component corresponding to the ceramic/internal electrode interface regions was more strongly degraded than the other three R components, and it was found that this component was the main factor responsible for the degradation of IR during the test. The resistance degradation of this component tended to occur slowly when the vanadium content increased, which resulted in the improvement in lifetime. The primary part of this degradation was implied to be controlled by diffusion.

Production of Metallic Particles Covered with Insulator Layer

Metallic particles covered with a silicon oxide layer have been produced for Ag and Pb by the gas evaporation method using an evaporated metal and SiO mixture powder. Metallic particles less than a few nanometers in diameter covered with a silicon oxide layer were produced under selected growth conditions. Cometlike particles were obtained only in a eutectic system of Ag–Si with a sufficient amount of SiO mixture powder relative to the Ag powder. The formation of Pb particles covered with a silicon oxide layer may enable new nanoparticle applications as a stable material taking environmental concerns into consideration.

New Insights into the Generation Mechanism of Quasicrystal by the Surface Reaction Between Ultrafine Particles and Deposited Clusters

On heating Mn-deposited Al particles (Mn–Al specimen) at 300°C, diffraction spots due to a Al86Mn14 quasicrystal appeared, in addition to those due to Al6Mn alloy. On heating a specimen of the Al-deposited Mn particles (Al–Mn specimen), Al50Mn50 alloy was formed. Neither the quasicrystal nor Al6Mn phases appeared. The electron microscope images of the Mn–Al specimen showed the existence of void clusters in the Al particles. This indicates that the alloys and the quasicrystals were produced by the diffusion of Al atoms to the Mn clusters. In the case of the Al–Mn specimen, the surface of Mn particles was covered with an Al thin film of uniform thickness. The surface Al layer changed to Al50Mn50 alloy. These results indicate that the diffusion direction of atoms and diffusion rates are different between Mn–Al and Al–Mn systems.

In situ observation of silicon carbide formation process using electron microscope

The silicon core and carbon mantle particles were produced by using the advanced carbon coating method which enables direct covering with the carbon layer using an electron microscope. The growth of SiC crystal was observed upon heating at 500°C in vacuum. The growth process of SiC on both the carbon layer and silicon particles was directly observed by in situ observation. The inward movement of carbon into silicon began at the twinned part. The growth rate of SiC on the carbon mantle layer was estimated from in situ images and found to be 8 times faster than the growth rate of silicon carbide in silicon particles.

Structure and Growth of Rod-Shaped Mn Ultrafine Particle

The structure of rod-shaped Mn ultrafine particles was elucidated by electron microscopy. Mn ultrafine particles have characteristic tristetrahedron (α-Mn), rhombic dodecahedron (β-Mn) and rod-shape crystal habits. It was found that the rod-shaped particle resulted from the parallel coalescence of β-Mn particles with the size of 50 nm. Detailed analysis of the defects seen in large rod-shaped particles with the width of 100 nm indicated a mixture of α- and β-phases. A size effect on the phase transition from β to α was observed throughout the rod-shaped crystal structure. The structure and growth of Mn particles were discussed based on the outline of the smoke and the temperature distribution in the smoke.