Gas Evaporation Technique Research Articles

The Study of Metal Colloids Produced by Means of Gas Evaporation Technique. I. Preparation Method and Optical Properties in Ethanol

Abstract Three new methods for the preparation of metal colloid in organic solvent are presented. These methods were the matrix isolation method, the gas flow-cold trap method and the gas flow–solution trap method; the latter was found to give a good colloid solution for the optical measurements. The metals reported are high purity Ag, Au, Cu, In, Al, Ca, Sn, and Pb. The stability of the colloid is dependent on the kind of metals: Al, In, Au, and Ag are stable, and Pb, Sn, Ca, and Cu are unstable. The optical absorption spectra of these sols were measured in ethanol solution in Ar atmosphere. They are discussed in relation to those reported on the solid matrix or on the solid substrate.

Growth of copper-gold and copper-aluminum particles by gas-evaporation technique

The composition, crystal structure and habit of Cu-Au and Cu-Al particles prepared by evaporation of mother alloys in argon gas were investigated by X-ray diffraction and electron microscopy. With the progress of evaporation, the Al concentration of the Cu-Al particle changed so as to fall at about 35 at%, while the Au concentration of the Cu-Au particles always increased up to 100 at%, irrespective of the composition of the starting materials. Both the Cu-Au particles over the whole range of Au concentration and the Cu-Al particles containing up to about 35 at% Al showed the same well-defined crystal habits as pure metal particles, corresponding to their crystal structures.

High-resolution observations of PbS adsorbed structures on Mg (00.1) surface

Characteristic surface structures and adsorbed structures of metals and semiconductors have been elucidated by reflection electron diffraction techniques such as LEED and RHEED. These techniques, however, can not give the information about the atomic arrangements or adsorbed sites in a direct way. The present work is the first trial of observing the adsorbed structures of PbS grown on Mg (00.1) surfaces with atomic resolution by using transmission electron microscopy. For such trials, the specimen preparation is the most important problem which decides the success of the observations. Especially, clean, flat and thin (∽10nm) substrates should be prepared.The present specimen substrates are Mg‐platelike particles prepared by gas evaporation technique. The procedure of the specimen preparation is as follows: Mg-platelike particles (thickness ∽ 20nm) are prepared by the evaporation of Mg ribbon in 10 Torr of argon and gathered on a perforated carbon films. After re-evacuation down to 1 × 10-8 Torr of the chamber, PbS of less than 1 nm in mean thickness is deposited on the Mg-plates.

Growth of CdTe smoke particles prepared by gas evaporation technique

CdTe smoke particles prepared by evaporating CdTe powder in Ar gas were studied by electron microscopy. The zinc-blende particles were formed in an atmosphere of Ar containing an excess Te vapor. The wurtzite particles were formed in an atmosphere of Ar containing an excess of Cd vapor. The lattice images of the CdTe crystal particles prepared by evaporating CdTe powder showed that the particles were composed of pure CdTe crystal. Tetrapod crystals with the wurtzite structure and with the zinc-blende structure grew from nuclei which have been identified to have the zinc-blende structure. A thin layer skin-like mechanism was observed on the particles formed by the excess Te vapor.

Raman study of Ge and GaP microcrystals

Raman scattering from Ge and GaP microcrystals prepared by gas evaporation technique has been investigated. In the case of Ge, the existance of amorphous particles of the order of 80Å in diameter was demonstrated. For crystalline Ge particles the size dependence of Raman spectra was observed. In the case of GaP, the surface phonon mode was clearly observed when the particles are about one order of magnitude smaller than the wavelenght of incident laser radiation.

Mössbauer effect study of the internal magnetic field in small iron particles

A temperature and size dependent enhancement of the internal magnetic field was observed for small iron particles produced by the gas evaporation technique and was explained by the demagnetization field and the dipole interaction of the particles. Thermal fluctuation of the magnetization and fusion between the particles have important effects.

Observation of PbS Grains Grown on Mg (00.1) Surfaces

Grains of PbS deposited on Mg (00.1) surfaces prepared by the gas evaporation technique are observed by using high resolution electron microscopy. Among the grains with various orientations, those with 100 and 110 orientations are observed. In the former grain, the contrast arising from the forbidden 110 reflection for PbS can be obtained due to the thin thickness. Two kinds of adsorption structures, a pseudomorphic structure and a new arrangement of Pb atoms, are found. An attempt to determine adsorption sites of the deposit is also carried out by comparison between the electron micrograph and the simulated images.

Crystal Structure and Morphology of Fine Particles of Vanadium Silicides

In this experiment, fine particles of various vanadium silicides were made by the gas-evaporation technique. The structure and morphology of the particles were observed by electron microscope. The A15 structure was found to appear at 20.0 and 25.0 at.%Si, while the D88 and D8m structures appeared at 35.2 and 37.5 at.%Si. The particles were surrounded by crystallographic planes with low Miller's indices characteristic of each structure. At 30.0 and 32.7 at.%Si, two types of particle were observed; one containing the A15 and D8m structures and the other the A15 and D88 structures. In the respective particles, the lattice relationships (001)A15//(001)D8m and [100]A15//[100]D8m, and (001)A15//(001)D88 and [110]A15//[120]D88, were found. These can be ascribed to the resemblance between the structures.

反応ガス蒸発法によるＩＩＩａ，ＩＶａ，Ｖａ及びＶＩａ属の窒化物超微粒子の生成

Preparation of ultrafine nitride particles has been performed using the reactive gas evaporation technique with electron beam heating. By evaporating metals of group IIIa, IVa, Va and VIa in an atmosphere of N2 or NH3 gas at about 1Torr, nine kinds of crystalline nitride particles, i. e. AlN, TiN, ZrN, HfN, VN, NbN, CrN, Mo2N and W2N, were produced. These particles were studied by means of electron microscopy and X-ray diffraction method. All the nitride particles were found to have a particle size smaller than 10nm, and were confirmed to be a single phase with the ordinary crystal structure: Wurtzite-type for AlN, NaCl-type for TiN, ZrN, HfN, VN, NbN and CrN, and partially disordered NaCl-type for Mo2N and W2N.The crucible-less evaporation method, which is free from impurities caused by a crucible damage, can be adoped for the most metals of group IVa, Va and VIa.

Raman scattering from the surface phonon mode in GaP microcrystals

The Raman scattering from GaP microcrystals prepared by a gas-evaporation technique has been investigated. A new peak, which can be identified with the surface phonon mode, was found. The present results demonstrate that the surface phonon peak can be clearly observed only when the microcrystals are about one order of magnitude smaller than the wavelength of the incident laser radiation.

Ultrafine powders of TiN and AlN produced by a reactive gas evaporation technique with electron beam heating

Ultrafine powders of TiN and AlN are produced by evaporating Ti and Al in a low pressure of NH 3 or N 2 gas by using electron beam heating. Powders produced are studied by means of electron microscopy and X-ray diffraction method. Both powders are confirmed to be pure nitride with cubic crystal structure for TiN and hexagonal for AlN, and to have a particle size less than 10 nm. The formation process of the nitride powder by the present method can be summarized as follows; (1) surface nitridation of the source materials, (2) vaporization of the nitride and (3) condensation into the nitride particles.

Ultrafine Powders of TiN, ZrN, HfN and AlN Produced by the Reactive Gas Evaporation Technique with Electron Beam Heating

Ultrafine Powders of TiN, ZrN, HfN and AlN Produced by the Reactive Gas Evaporation Technique with Electron Beam Heating

Magnesium Twinned Particles Grown in Inert Gases

Twinned particles of magnesium prepared using the gas evaporation technique were studied using electron microscopy. Particles with (10.1), (10.3), (11.1) and (11.2) twin planes were found in the smoke outer zone. Their external faces were the same as those of single crystal particles, i.e. {10.0} and (00.1). The growth of the (10.1) twinned particle was more pronounced than that of the other three kinds of twinned particles and from this it was deduced that the twin formation occurs at the nucleation stage.

X-ray diffraction study of fine gold particles prepared by gas evaporation technique

From the analysis of the X-ray Debye-Scherrer lines of the fine gold particles of which sizes are in a range from 60 to 230 Å, it was found that the thermal expansion coefficient as well as the lattice parameter are not different from those of the bulk crystal, while the characteristic temperature decreases monotonously with the decrease of the particle size. The particle size dependence of the characteristic temperature can be explained by introducing two characteristic temperatures θ core and θ shell, on the assumption that the particles are composed of the core and the shell. θ core and θ shell were found in good agreement with the characteristic temperature for the bulk crystal and that for the surface obtained by LEED experiment, respectively.

Optical properties of granular metal films: The Au/Ag system

Silver, gold and Ag/Au films were prepared by the gas evaporation technique. The optical transmittances are reported. Our measured data are well reproduced by a modified Garnett formalism.

X-ray diffraction study of fine gold particles prepared by gas evaporation technique

X-ray diffraction study of fine gold particles prepared by gas evaporation technique

Structure and growth of ZnO smoke particles prepared by gas evaporation technique

ZnO smoke particles prepared by burning zinc metal in a gas mixture of 80% Ar and 20% O 2 at a total pressure of 100 Torr were studied by electron microscopy. The ZnO particles were formed by the oxidation of evaporated zinc vapor in the gas phase. It was found that the particles less than 20 nm in size have the zinc-blende structure. They became tetrapod-like crystals by fast growing along four 〈111〉 directions perpendicular to the {111} or Zn faces. Then, wurtzite crystals formed on their {111} faces by introduced stacking faults, and they grew along their easy growth [0001] directions, and became well-known “fourlings” composed of four needle crystals.

Sintering of Ultrafine Metal Powders. I. Coalescence Growth Stage of Au and Ag

Sintering of ultrafine powders of Au and Ag, produced by a gas evaporation technique, has been studied by the electron microscopy and X-ray diffraction methods. The critical temperature, above which the particle size increases, is found to be room temperature for Au powders and 60°C for Ag powders with a particle size of about 200 Å. Retardation of sintering is observed for both Au and Ag powders exposed to air before heating. Decrease of strains as well as stacking disorders with increase of temperature is detected by X-ray diffraction and electron microscopic study. Experimental formulae for the variations of particle size and strain with temperature are obtained from the half-value breadth of X-ray diffraction profile. Particle size effect on sintering is also examined for Ag powders.

X-Ray Diffraction Study of Fine Gold Particles Prepared by Gas Evaporation Technique. I. General Feature

Fine gold particles prepared by gas evaporation technique were characterized by X-ray powder diffraction method. Several anomalies which acre similar to those found in the cold worked metal fillings were found in the Debye-Scherrer pattern. Obvious differences in lattice parameter and the thermal expansion coefficient were not detected between the fine gold particles with the mean size of 100 A and bulk crystal. The mean square atomic displacement estimated from the Debye-Waller factor, however, shows sometimes values twice as large as that of the bulk crystal, depending on specimen preparation. It is shown that a considerable contribution from static lattice distortions is included in the mean square atomic displacement.

X-Ray Diffraction Study of Fine Gold Particles Prepared by Gas Evaporation Technique. II. Characteristic Temperature

From an analysis of the X-ray Debye-Scherrer lines from fine gold particles with the mean size of 100 A, the mean square atomic displacement, , was determined at several temperatures in a range from 112 to 298 K. The temperature dependence of was analysed on the basis of the Einstein approximation for the thermal vibrations of atoms and a characteristic temperature θ M =143±3 K was obtained. This is 15% less than the Debye temperature θ M =168 K for the bulk crystal. It was found that the observed includes the temperature independent component, impling the existence of some kind of static lattice distortions. The contribution from such lattice distortions depends on the preparation condition of fine gold particles.