Kazuo Kimoto

An Electron Microscope and Electron Diffraction Study of Fine Smoke Particles Prepared by Evaporation in Argon Gas at Low Pressures (II)

This paper forms a continuation of the previous paper of almost the same title (Kimoto et al., Japan. J. appl. Phys. 2 (1963) 702). The materials examined include all the metals studied in the previous paper, Mg, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Cd, Sn, Au, Pb and Bi plus the five elements, Be, Ga, Se, In and Te which have been newly added. One of the advances in the present study is the improved purity of the argon used. Thus, beautiful crystal habits have been observed for many of the elements. A small amount of oxygen, for example 0.03 mm Hg of oxygen in 6 mm Hg of argon, caused remarkable deterioration in the crystal habit of the particles. New modifications of crystal structure were found among the particles of chromium aud manganese. A few of the previous results are corrected because they were found to be due to impurities in the argon.

An Electron Diffraction Study on the Crystal Structure of a New Modification of Chromium

Fine particles of chromium were produced by evaporation and condensation of chromium in argon at low pressures (Kimoto et al. : Japan. J. appl. Phys. 2 (1963) 702). Electron diffraction studies have shown that the particles have the ordinary b.c.c structure of chromium when the argon contains a small amount of air or oxygen but they have a new structure when the argon is pure. The new structure has a cubic primitive lattice with lattice constant a 0 =4.588±0.001 A. The unit cell contains eight chromium atoms; the probable space group is Pm3; one atom occupies position (a) 000, one atom occupies position (b) \(\frac{1}{2}\frac{1}{2}\frac{1}{2}\) and the remaining six atoms distribute themselves so that on the average one-quarter of an atom occupies each of the 24-fold position (1) x y z ; where \(x{=}\frac{1}{4}-u\), y = v , \(z{=}\frac{1}{2}+w\) with parameters u =0.2/100, v =4/100 and w =1/100. This is a disordered atomic arrangement derivable from the β-tungsten structure. The shortest Cr-Cr distance is...

Crystal habit and crystal structure of fine chromium particles: An electron microscope and electron diffraction study of fine metallic particles prepared by evaporation in argon at low pressures (III)

Fine Cr particles formed by evaporation in argon at low pressures were found to have well-defined crystal habits corresponding to the following solids: (i) the icositetrahedron bounded by 24 {211} planes; (ii) the rhombic dodecahedron bounded by 12 {110} planes; and (iii) the cube or the rectangular parallelepiped bounded by six {100} planes. The first two particle shapes were consistent with δ-Cr and the third with ordinary b.c.c. Cr. Re-examination of the crystal structure of δ-Cr by means of fine single crystals suggested that it was consistent with the A-15 type structure proposed by Forssell and Persson (J. Phys. Soc. Japan, 29 (1970) 1532). A disordered structure derivable from the A-15 type, reported previously by the present authors, is therefore withdrawn.

The Crystal Habits of Small Particles of Aluminium and Silver Prepared by Evaporation in Clean Atmosphere of Argon

The crystal morphology of small particles of aluminium and silver made by evaporation under very clean conditions in 99.99% pure argon at 10~20 Torr has been studied by electron microscopy and electron diffraction. The sum of the partial pressures of the residual gases other than argon in the evaporation chamber at the time of evaporation was of the order of 10-9 Torr. The individual aluminium particles thus obtained had the shape of a cubo-octahedron with smoothly curved edges and corners, and the silver particles were mainly multiply-twinned with icosahedral shape. Comparisons are made between the present results and those already obtained from the small particles made in an ordinary vacuum chamber.

Oblique incidence effect on the crystal structure of thin vacuum-deposited chromium films

Abstract It has been found that thin films of chromium made by oblique incidence in vacuum deposition consist of the new modification of chromium (δ-Cr 1 .) in addition to ordinary b.c.c. α-Cr. For uniform films with thickness between approximately 10 and 70 A, the ratio of the amount of δ-Cr to α-Cr increased as the obliqueness of the incident vapour stream increased. When the mean thickness exceeded about 100 A. δ-Cr ceased to be obseved and only b.c.c. α-Cr remained, irrespective of the incidence angles. On the other hand, when the mean thickness was about 10A diffuse halo patterns were observed. Dark field electron microscopy revealed that the crystal size of the δ-Cr was much smaller than that of the α-Cr.

A Study of Lithium Clusters by Means of a Mass Analyzer

Lithium clusters containing up to 15 atoms were prepared by evaporation in an inert gas at a pressure of 10 -4 ∼10 -3 Torr and the mass numbers of these clusters were measured by a mass analyzer. The following are the main results. i) In good vacuum lithium was detected as single atoms. ii) When an inert gas was present, Li 2 , Li 4 , Li 6 and Li 8 were always detected; however, Li 3 and Li 5 were never detected. Li 7 and Li 9 were detected in smaller amounts than those of neighbouring clusters. iii) In the range Li 10 to Li 15 all possible clusters were detected and Li 13 was most abundant among them.

Crystal structure of very small particles of chromium and iron

Abstract Very small crystals of chromium with diameters less than about 30 A, formed by vacuum deposition onto a substrate at room temperature, gave rise to an electron diffraction pattern consisting of diffuse haloes. It was concluded that these haloes could not be interpreted in terms of the ordinary b.c.c. structure of chromium but could be interpreted in terms of the new modification of chromium called δ-Cr. This conclusion was drawn by comparing the observed intensity profiles of the diffraction haloes with those calculated from the scattering formula for gas molecules, assuming that the molecules had given numbers of atoms arranged in the δ-Cr structure. Particles of iron also showed similar halo patterns when the particles were very small. The iron and chromium particles all had their normal b.c.c. structures when their sizes exceeded 20 and 100 A, respectively.

Electron Microscope and Electron Diffraction Study of Fine Particles Prepared by Evaporation in Argon at Low Pressure. IV. Fine Particles of Tellurium

Tellurium particles produced by evaporation in argon at a pressure of several Torr are observed to occur with two distinct shapes. They are either spherical or egg-shaped or else they are rod-shaped. The rods are hexagonal in cross section, bounded by {10.0} planes and have their axes parallel to the [00.1] direction. Both kinds of particle are single crystals with the normal hexagonal structure of α-tellurium. They nucleate and grow in different zones of the tellurium smoke. The fact that particles grown in different zones have different shapes is explained in terms of the temperature dependence of the spatial anisotropy of the γ-plot where γ is the specific surface free energy.

A Study of Lithium Clusters by Means of a Quadrupole Mass Analyzer

Lithium clusters were prepared by evaporating lithium in argon at a pressure of 10-4~10-2 Torr and the mass numbers of these clusters containing up to 15 atoms and their relative abundances were measured by a quadrupole mass analyzer. In good vacuum lithium was detected as single, electrically neutral atoms. When argon was present, clusters composed of an even number of atoms were always detected. Li3 and Li5 were never detected and in the range Li7 to Li15, clusters composed of an odd number of atoms were detected in smaller amounts than was the case for neighbouring clusters containing an even number of atoms.

Magnetic Properties of δ-Cr and bcc Cr Fine Particles Prepared by Gas Evaporation Method

Both field- and temperature-dependences of the magnetization of the fine particles of δ-Cr (A-15 type structure Cr) and of bcc Cr are studied. The δ-Cr particles show temperature-independent paramagnetism. The bcc Cr particles show weak ferromagnetism below 850 K. The ferromagnetism probably originates in the surface magnetism due to the high density of states of electrons at the surface.