Masato Tada

Recovery of the Quenched-In Solute Hydrogen Atoms in Nickel

The recovery process of hydrogen dissolved in excess in nickel is studied by means of the liquid hydrogen quenching method which is a modified Schultzs method. A recovery stage of electrical resistance is found in the range 190K~380K in the isochronal annealing curves. It is found that during the annealing the dissolved hydrogen atoms diffuse to and escape out of the surface of the specimen producing the timewise and spacewise varying distribution of concentration in the interior. The resistance of the specimen is calculated by using an equivalent circuit of the parallel connection of concentric hollow cylinders having different values of electrical resistivity depending on the hydrogen concentration which can be obtained from the diffusion equation. Extremely good agreement is obtained between the experiment and calculation, and the diffusion coefficient is determined as D=2.14×10-3exp (-8880/RT) cm2/sec.

Structure of an extremely thin film of a-SiO2

Abstract By means of electron beam evaporation, we have succeeded inpreparing a substrate-free amorphous SiO 2 (a-SO 2 ) film 4A in thickness for electron diffraction study. The analysis of the diffraction intensity from the film has detected atomic distances of 1.54A and 2.48A as those of Si-0 bond distance and O--O distance; which are considerably shorter than Si O bond distance and O--O distance observed by X-ray diffraction in ordinary a-SO 2 : 1.62A and 2.65A. This result reveals that the structure of extremely thin a-SO 2 film is different from the bulk structure in a-SO 2 material.

High Energy Electron Diffraction Study on Ionic Character of Amorphous SiO2

The structure of amorphous SiO2 film prepared by electron-beam evaporation has been investigated. The structural parameters of the shortest Si-O, O-O and Si-Si atomic pairs were determined from the radial distribution function by the least-squares method. Regarding the structural analysis of the evaporated amorphous SiO2 (ev.a-SiO2), the scattering factors for neutral and ionized atoms were used in order to investigate the ionic character of SiO2. The obtained values for each atomic distance did not vary with the scattering factors used, but the obtained number of each atomic pair was greatly dependent on the factors. From the results of the structural parameters, it was found that ev.a-SiO2 is constructed from basic silicate tetrahadrons, and that the constituent silicon and oxygen atoms have some ionic character.

Recovery of Pure Iron Quenched-in Liquid Hydrogen

A new method of hydrogenation and quenching of metals in liquid hydrogen, i.e. the hydrogen quenching method, is developed and applied to investigate the recovery of pure iron after the hydrogenation and quenching by measuring the electrical resistivity change during annealing at higher temperatures. A new stage corresponding to the migration and disappearance of solute hydrogen atoms in pure iron appears in the resistivity decay curve, and by an approximate analysis based upon the rate process calculation the migration energy of single interstitial hydrogen atoms is determined to be 2.2±0.2 kcal/mol. In the diffusion process, most of the solute hydrogen atoms are discharged at the free surface of the specimen, but, in order to fully explain the resistivity decay curves, the influence of trapping sites or sinks for hydrogen in the interior must be also considered.

Structural analysis of SiO2 gel films by high energy electron diffraction: Code: CP3

The structure of SiO2 gel-films prepared from acid and basic TEOS solutions is analyzed by high energy transmission electron diffraction method. The Si-O bond length of gel-films is 1.58 to 1.60 Å, which is shorter than that of vitreous silica (1.61 Å) but similar to that of 80 Å thick evaporated a-SiO2 film. An atomic pair peak with 0.81 Å distance exists on the reduced radial distribution functions of the gel-films, which is believed to be O-H, but being smaller than that of H2O (0.969 Å).

Structural difference of surface and sub-surface native oxides of evaporated amorphous silicon

Abstract Evaporated amorphous silicon (a-Si) films, oxidized in air or O 2 at room temperature, present two native oxides with different structures. The surface oxide is constructed from SiO 4 -tetrahedron structural units with a 110° OSiO angle, which is the common structural unit of stable silicon oxides. The internal oxide has a different structure having a 120° OSiO angle. The results of molecular orbital (MO) calculations for (SiO 3 ) m − and (SiO 4 ) n − anionic clusters support the presence of the two stable structures of silicon oxides and also reveal the importance of the ionic character of the oxidized sites.

Formation mechanism of evaporated a-SiO2: An approach from the oxidation processes of a-Si

Abstract The formation mechanism of evaporated amorphous silicon dioxide (a-SiO2) films was studied on the basis of the structural comparison between a-SiO2 and the oxides of evaporated amorphous silicon (a-Si) by use of transmission electron diffraction. The mechanism is found to be separated into the two following steps: the first is the construction of the transient structure with an O-Si-O angle of 120° caused by the reaction of the vapor species on the deposited surface: the second is the reconstruction into the permanent structure with an O-Si-O angle of 110° on the surface.