Ryozi Uyeda

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.

The morphology of fine metal crystallites

Abstract Clear-cut habits were found for fine metal crystallites formed by evaporation of a metal in an atmosphere of inactive gases; helium, argon and xenon. A systematic investigation by electron microscopy on twenty-two kinds of metal for various formation conditions was carried out. Some of the distinct morphologies found so for are as follows: (1) Cubes for α-Cr, (2) octahedra for fcc metals, (3) rhombic dodecahedra for α-Fe, β-Mn and Be, (4) tristetrahedra for α-Mn, (5) icosatetrahedra for δ-Cr, (6) hexagonal plates and polyhedra for Be, Mg and Zn, (7) hexagonal rods with split ends for Te, (8) truncated triangular biprisms fcc metals, (9) pentagonal decahedra and/or icosahedra for fcc metals and γ-Fe. Nos. 1 to 7 are single crystals, No. 8 are twinned and No. 9 are so-called multiply-twinned particles. Among the single crystals, the octahedra and rhombic dodecahedra, which are more or less truncated in many cases, are possibly Wulff polyhedra for fcc and bcc crystals, respectively.

Magnetic Properties of Ferromagnetic Metal Fine Particles Prepared by Evaporation in Argon Gas

Fine particles of Fe, Co and Ni were prepared by evaporation in the atmosphere of argon gas at low pressure. The diameters of the particles ranged from about 100 A to 2000 A. Magnetization of particles was measured by magnetic balance. For Fe and Co the saturation magnetization of the finest and the most coarse particles were about 20 per cent and 90 per cent of those of bulk metals, respectively. For Ni, it was more than 80 per cent and the particle size dependence was less than for Fe and Co. The remanent magnetization and the coercive force were largest for the particle diameter of 300 A of Fe and Co. The effect of superparamagnetism for smaller particles was not observed. When deposited in magnetic field, long chains of particles appeared along the field direction. Such specimens showed hysteresis curves much more convex than that of randomly oriented ones and remanent magnetization twice as large.

Formation of Ultrafine Metal Particles by Gas-Evaporation VI. Bcc Metals, Fe, V, Nb, Ta, Cr, Mo and W

The crystal structures and habits of bcc metal particles have been investigated systematically by electron microscopy. The habits for the bcc structure are rhombic dodecahedra truncated by six {100} faces with various degrees of truncation from 0 to 100%. The truncation degree for Fe and V particles grown in the intermediate zone of a metal smoke is in good agreement with that for the Wulff polyhedron expected from the surface energies calculated for {110} and {100} faces. Particles of Cr, Mo and W have the A-15 type structure besides the ordinary bcc structure. The present results support the hypothesis that the A-15 type structure is stable when the particle size is small. The habits for the A-15 type structure are rhombic dodecahedra (Cr), {211} icositetrahedra (Cr and Mo) and rounded cubes (Mo and W).

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.

Effect of Incoherent Waves on the Electron Microscopic Images of Crystals

The electron micrographs of crystalline specimens are taken by placing the aperture of the objective lens at various positions. Extinction contours, equal-thickness fringes and dislocation images are observed under a condition that none of the coherent waves–the transmitted and diffracted waves–enters the aperture. This implies that the above contrast effects are formed by incoherent waves which are neglected in current theories of diffraction contrast.

Electron Microscope Study on the Extinction and Absorption of 100 kV Electrons in Magnesium Oxide Single Crystals

The intensity profile of equal thickness fringes due to 200 reflection was studied by the photographic method. The orientation of the specimen crystal was systematically changed by use of a tilting stage in the electron microscope. The real part of 200-Fourier coefficient and the imaginary part of the mean inner potential were determined to be V200r=7.43±0.11 volt and V0i=0.58±0.04 volt, respectively, provided no simultaneous reflection took place. When the deviation from the exact Bragg position, viz. the Bethes parameter W, was varied, the behavior of intensity profile was found to be entirely different from that predicted by the two-beam approximation of the dynamical theory assuming the phenomenological complex potential. It was shown that the so-called anomalous transmission in the case of electrons can not be ascribed to the decrease of effective absorption coefficient at the Bragg position.

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.