Shigeki Yatsuya

Formation of Ultrafine Metal Particles by Gas Evaporation Technique. I. Aluminium in Helium

The appearance of smoke was studied by a video tape recorder. A typical smoke consisted of inner zone, inner front, outer zone and outer front. Smoke particles collected at different parts were studied by electron microscopy. They were large and often showed clear-cut habits in the inner front, while they were small and uniform in the inner and outer zones. The particle size varied with the gas pressure, evaporation temperature and position of collecting particles. The particles grow remarkably by coalescence where no metal vapour exists. All the experimental results on the size can be explained with an empirical rule that particles become larger when the nucleation starts in vapour of higher density.

Formation of Ultrafine Metal Particles by Gas-Evaporation Technique. IV. Crystal Habits of Iron and Fcc Metals, Al, Co, Ni, Cu, Pd, Ag, In, Au and Pb

Fine metal crystallites with diameters 200~2000 A made by evaporating a metal in an atmosphere of an inactive gas were studied by electron microscopy. It is found that the crystal habit common to Be, Cr, Mn and Fe, which are bcc just below the melting point, is rhombic dodecahedra truncated by {100}. Fcc metals show six different types of crystal habit. However,only one, viz. octahedra truncated by {100}, is a single crystal and all the others have twins. Various degrees of truncation were found both for rhombic dodecahedra and octahedra. Crystallites with certain degrees of truncation are possibly Wulff polyhedra.

Magnetic properties of ferromagnetic ultrafine particles prepared by vacuum evaporation on running oil substrate

Abstract Ultrafine particles of ferromagnetic metals (Fe, Co and Ni) were prepared by the vacuum evaporation onto a running oil substrate. Particles thus obtained were suspended in the oil and their average diameter was about 25 A. An electron diffraction analysis indicated that the particles were oxidized and the main component was Fe 3 O 4 , CoO and NiO for Fe, Co and Ni fine particles, respectively. From magnetic measurements in the temperature range between 4.2 and 300 K, the main magnetic behavior of the fine particles can be explained in terms of the superparamagnetism or superantiferromagnetism. Furthermore, it was concluded that the Fe 3 O 4 particles may be covered with several atomic layers of α-Fe 2 O 3 . For CoO and NiO particles, existence of an imperfect oxide structure was required besides the main components in order to explain the magnetic behavior.

Preparation of extremely fine particles by vacuum evaporation onto a running oil substrate

Abstract A large amount of extremely fine particles of Ag were prepared by vacuum evaporation onto a running oil substrate. The size distribution of Ag particles thus prepared was studied by electron microscopy. It was found that the mean diameter of the particles strongly depends upon the deposition rate, and kind and viscosity of the oil. Particles of mean dimater from 30 to 80 A can be produced. The sticking coefficient on the oil surface for arriving atoms is, in general, smaller than that on a glass surface. The coefficient increases with increasing viscosity for the same kind of oil. Coalescence growth of particles is also detected by heating the oil containing the particles. The heat treatment also enables us to control the practicle size between 30 to 80 A.

Ultrafine Metal Particles Formed by Gas-Evaporation Technique. : II. Crystal Habits of Magnesium, Manganese, Beryllium and Tellurium

Particle samples collected at various positions in metal smokes were studied by electron microscopy. The size and shape of the particles varied with the collection positions as well as with the evaporation conditions such as the gas pressure and evaporation temperature. The results showed a general trend that the crystallites with larger surface area formed in the outer zone while those with smaller surface area formed in the inner zone, provided that their volume was the same: hexagonal plates (Mg & Be) and rods (Mn & Te) formed in the outer zone while hexagonal polyhedra (Mg), rhombic dodecahedra (Be & Mn) and pear-shapes (Te) formed in the inner zone.

Formation of Ultrafine Metal Particles by Gas-Evaporation Technique. III. Al in He, Ar and Xe, and Mg in Mixtures of Inactive Gas and Air

Aluminium smokes in He, Ar and Xe at various pressures were studied. Their macroscopic shapes were roughly the same in 200 Torr He, 10 Torr Ar and l Torr Xe. Under these conditions the particle size in the inner zone of a smoke decreased with the molecular weight of the gas. In the course of the experiment, several electron micrographs showing the intermediate stages of particle coalescence in the smoke were obtained. When an inactive gas contained oxygen, the smoke particles were almost perfectly oxidized in the outer zone of the smoke, while the oxidation was slight in the inner zone.

Magnetic Properties of Extremely Fine Particles of Iron Prepared by Vacuum Evaporation on Running Oil Substrate

Extremely fine particles of iron were prepared by vacuum evaporation onto a running oil substrate. Particles thus prepared were suspended in the oil and their average diameter was about 25 A. From the electron diffraction analysis, it is found that the main constituent of the suspended particles is Fe3O4. Magnetic measurements revealed that these particles showed superparamagnetism whose blocking temperature was distributed between 10 and 30 K, and that the magnetic interaction among these particles was negligibly small.

A New Technique for the Formation of Ultrafine Particles by Sputtering

A gas evaporation technique using sputtering is newly developed. The characteristic of this new technique is the use of sputtering in an atmosphere of higher gas pressure such as 0.5 to 100 Torr than is used for ordinary sputtering. W, Ag and Cu are tested and their ultrafine particles are formed. WC1-x particles are also prepared by reactive sputtering.

Attempt to form hydride and amorphous particles, and introduction of a new evaporation method

Al and TiH2 particles of fcc structure can be produced in an atmosphere of gaseous H2 at reduced pressure. Al particles with definite habit are obtained, which has been never observed in the ordinary gas evaporation technique using a HV system. The habit of TiH2 particles grown in the intermediate zone of the smoke is determined to be a dodecahedron. The growth is considered as the result of the martensite transformation from the bcc structure initially formed to the fcc structure accompanying a slight modification of the characteristic habit as observed for Ti particles. For the preparation of amorphous particles, first, the quenching rate of a particle, dTdt was estimated to be more than 104°Cs. Ultrafine particles of Pd80Si20 chosen as a test sample did not show the amorphous structure, but the crystalline. Application of the sputtering method as a new evaporation source in the gas evaporation technique is attempted. With the sputtering method, W particles with definite habits are produced.

Formation of Ultrafine Particles by Gas-Evaporation Technique. : V.Silicon and Germanium in Argon

Fine particles of silicon and germanium were prepared by evaporation in argon gas at low pressures, and they were studied by electron microscopy. Relatively large particles showed distinct crystal habits for both materials. A typical habit of silicon was an polyhedron bounded by twenty four {311} and eight {111} faces, and that of germanium, an icositetrahedron bounded by {311} faces. Crystallites with these habits have the diamond structure as usual. However, relatively small germanium particles, which were formed in the inner part of the smoke, showed no distinct habit and had an unknown structure with a tetragonal unit cell, a=5.37 A and c=9.04 A.