Toshiaki Tanigaki

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.

Novel method for the preparation of silicon oxide layer on TiO2 particle and dynamic behavior of silicon oxide layer on TiO2 particle

Abstract Two methods for the preparation of TiO2 particles using the gas evaporation methods have been proposed. A method for selective growth of the anatase and/or rutile particles as well as a method of covering TiO2 particles with an SiO2 layer has been developed. The process of dissolving the SiO2 layer into TiO2 particles has been observed by an in situ observation using high-resolution electron microscopy. SiO2 layers of 5 nm order were dissolved completely into TiO2 particles of the order of 30 nm at 750°C. These SiO2 layers appeared again at room temperature on the surfaces of TiO2 particles. This phenomenon was observed only at a high temperature. By the use of the phenomenon of dissolving the SiO2 layer into TiO2 particles at high temperature, the growth of TiO2 particles covered with the SiO2 layer has been discussed.

A New Preparation Method of ZnO Cubic Phase Particle and Its IR Spectrum

ZnO ultrafine particles were produced by dropping Zn powder into a nichrome boat heated above 1000°C in a mixture gas of argon and oxygen. Cubic ZnO particles were predominantly produced in the mixture gas of oxygen at 5 Torr and argon at 95 Torr. The well-known hexagonal smoke particles were predominantly produced in the mixture gas of oxygen partial pressure of more than 20 Torr in the total pressure of 100 Torr. The characteristic infrared (IR) spectra due to the cubic and hexagonal phase were observed experimentally. The IR spectra of samples embedded in KBr pellets exhibited a peak at 20.3 µm wavelength for the cubic phase, and 18.3 µm and 23.0 µm wavelength for the hexagonal phase. The existence of cubic nuclei at the center of the tetrapod shape has been confirmed from the IR spectra.

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.

Process of crystallization in thin amorphous tin oxide film

Abstract Amorphous tin oxide films deposited on carbon substrates have been studied by high-resolution transmission electron microscopy. As-deposited film was composed of a mixture of microcrystallites of SnO, SnO 2 and SnO 3 with size of 2xa0nm. Crystallization took place above 450°C. SnO crystals appeared between 450°C and 500°C, whereas SnO 2 crystals appeared above 550°C. The appearance of β -tin crystals with the reduction of tin oxide has been verified using the heating stage of the electron microscope. A drop of liquid tin was recognized upon heating above 500°C. The difference in crystallization upon applying an electron beam, synchrotron radiation and heating in vacuum has been summarized and discussed with respect to the problem of the excitation of crystallites.

Structure of Carbon-coated or Silicon-oxide-coated ZnTe, ZnSe and ZnS Nanoparticles Produced by Gas Evaporation Technique

Ultrafine particles of typical chalcogenides have been produced by the advanced gas evaporation method (AGEM) and characterized by transmission electron microscopy. Zinc-blende nanoparticles less than 20-nm in size covered with SiO or carbon layer have been predominately produced. Many growth faults were observed in the zinc-blende particles above 20-nm in size. It has been found that particles less than 10-nm in size have no growth faults.

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.

Direct observation of the metamorphism of silicon oxide grains

Experimental studies on the metamorphism ofxa0SiO x xa0grains under heating atxa010 -6 xa0Pa have been conducted using a high-resolution transmission electron microscope. Sixa0crystallites were predominantly grown atxa0500 toxa0700xa0°C in SiO x xa0grains. The Sixa0crystallites disappeared atxa0800xa0°C and evaporated as the SiOxa0phase.

Dynamic behavior of Au cluster on the surface of silicon nanoparticles

Abstract The high-temperature behavior of Au clusters on a Si nanoparticle surface has been studied using the atomic-resolution high-temperature stage of a transmission electron microscope. Au atoms diffuse into the Si nanoparticle at 680°C and return to the surface at room temperature. The movement of diffused Au atoms on the Si surface steps and the movement of Guinier–Preston-zone-like contrast observed for the segregation of Au atoms on the (1 1 1) Si plane, have been directly observed. These phenomena, which can be detected only at high temperatures, are presented in this paper.