Chihiro Kaito

Studies on the structure and morphology of ultrafine particles of metallic sulfides

Abstract Ultrafine particles of metallic sulfides have been produced by the reaction of metal and sulfur vapor. The sulfur vapor was prepared by evaporating sulfur powder from a quartz boat using the atmospheric temperature of either the heated metal or the boat. PbS particles grew as single crystal cubes. β-In 2 S 3 particles grew as single crystal octahedra. Mo 3 S 4 , W 3 S 4 , Bi 2 S 3 , β-SnS 2 and β-Cu 2 S particles grew as thin plates. Sb 2 S 3 grew as amorphous spheres. Ag 2 S, α-In 2 S 3 and Sb 2 S 3 grew as complicated polyhedra. It is shown by HREM images that the coalescence growth took place in the metallic sulfide smokes.

Electron microscopic studies on structures and reduction process of copper oxide whiskers

Abstract Whiskers having a length of a few μm were grown by the oxidation of a copper standard electron microscopic grid in a furnace at 450°C in air. The whiskers were then studied by electron microscopy. The whiskers were composed of cupric oxide, paramelaconite (6CuO·Cu 2 O) and a mixture of both CuO and 6CuO·Cu 2 O. Most of the whiskers consisted of a bundle structure as the result of successive growth along to the side surface. By reducing the CuO whiskers in vacuum at 350 to 400°C, saw-toothed shaped crystals of cuprous oxide did appear which did have with the whiskers a topotactical relation such as (110) CuO • (100) Cu 2 O , [001] CuO • [110] Cu 2 O .

Molecular energetics of the growth mechanism of stearic acid thin films prepared by vacuum-deposition

Abstract Stearic acid crystals grew with different types of orientation on various substrates. The molecules lie parallel to the substrates (P-orientation) or stand normal to those (N-orientation). The proportion of P-orientation in the thin film decreases with increasing substrate temperature and also with decreasing deposition rates. Energy calculations have been carried out in order to describe the growth mechanism of the stearic acid on a KCl surface. The net charge distribution in the molecule is presented. The total potential energy, as well as the Coulomb and Lennard-Jones 6–12 potential contributions have been calculated for a single molecule with different orientations. It was clarified that the potential energy became minimal when the molecule was parallel to the substrate. The growth mechanism is discussed on the basis of the calculated potential energy.

Structure and crystallization process of a thin film prepared by vacuum evaporation of SnO2 powder

Abstract An amorphous tin oxide film 10 nm thick has been prepared by vacuum evaporation of SnO 2 powder from a tungsten boat onto a cleaved surface of rock salt. Analyses of electron diffraction patterns and high resolution electron microscope (HREM) images showed that the film was composed of microcrystallites of SnO 3 , 2.5 nm in size. An electron beam of the order of 0.1 A/mm 2 was used to irradiate the film, causing the micro-crystallites to change to the rutile structure of SnO 2 with a crystallite size of a few tens of nm. On further irradiation with an intense electron beam, SnO crystals about 10 nm in size appeared. A further increase in radiation energy resulted in larger crystallites containing crystal shear (CS) structures of two types in reduced SnO crystals. The growth process of SnO 2 , SnO and CS structure of SnO are discussed on the basis of the prefered orientation of formed crystals.

Initial stage of epitaxial growth mechanism of cadmium arachidate prepared by physical vapour deposition on various substrates

It is found that when it is deposited on a solid surface at 25°C at a pressure of 1x10-8 Torr with a thickness less than 0.5 nm, cadmium arachidate forms a molecular aggregate with a diameter of 100–500 nm. In these aggregations, the long chain molecules make an orientation with the chain axes normal to the substrate surface. Just after nucleation occurs, the molecular aggregates seem to be of a meta-stable state and subsequently transform to stable crystalline phases of slender or planar shapes depending on the kinds of substrate. On the KCl substrate, needle-like crystals are generated to grow along two directions corresponding to the <110 & axes of KCl. The planar crystals on mica show the periphery parallel to each other, while those on carbon film have no correlation. These results exhibit that the long chain molecules grow epitaxially on the KCl (mica) substrate with parallel (normal) molecular orientations.

Growth of ultrafine particles of II-VI compounds by a new gas evaporation method

Ultrafine particles of II-VI compounds have been produced by a reaction of group II and VI vapors in a convective flow of argon gas. Zinc-blende and wurtzite particles of ZnS, ZnSe, ZnTe, US, CdSe, and CdTe were produced. The particles with the zinc-blende structure were smaller than the wurtzite particles. Particles containing both the zinc-blende and wurtzite structures were observed. The existence of growth faults in particles was also seen.

High resolution electron microscopic studies of defects in CdTe smoke particles

Abstract Atomic resolution electron microscopy was carried our for CdTe smoke particles containing defects. Direct evidence for the coalescence growth in smoke was shown by the determination of the nature of stacking faults.

Magnetic field effect on the growth of ultra fine ferromagnetic metal particles

Abstract In order to make clear the effects of a magnetic field on the growth of ultra fine particles, electron microscope studies have been made on iron, cobalt and nickel particles prepared in different magnetic field strengths. The ultra fine particles were arranged in zigzag chains and straight chains. The zigzag chain can be explained by the connection of particles where each particle has a closed magnetic domain. The straight chain can be explained by connection of particles with each particle having a single domain. The strength of the magnetic field appearing in the straight chain was different for the ferromagnetic substances. These differences have been discussed on the basis of the coalescent growth in a smoke and the saturation magnetism of the substance.

A new experimental study on the production of clusters from copper ultrafine particles

Copper clusters were produced by successive processes of oxidation and reduction of copper ultrafine particles. The oxide produced was cuprous oxide (Cu 2 O). Partly oxidized particles were converted to the original copper particles by the reduction. Completely oxidized copper particles become a spherical shell composed of microcrystallites of cuprous oxide. By the reduction of spherical shell particles, microclusters of 2-10 nm in size were produced.

Structure of oxide particles produced by the reaction between Mg ultrafine particle and SiO film

Abstract A new experimental method to produce the compound by the use of reaction between vacuum evaporated film and ultrafine particles has been used for the system of Mg ultrafine particle and SiO film. In addition to the MgO particle, the enstatite phase (MgSiO3) was produced by heating at 450–700°C. The growth of the MgSiO3 phase has been discussed due to the movement of the Mg atom into the amorphous SiO film.