Eiji Hashimoto

Thermomigration of Scandium in Aluminum

The redistribution of scandium in polycrystalline A1-0.04 at ppm Sc dilute alloy which was annealed under a temperature gradient was investigated by means of the neutron activation analysis. The remarkable result is that the concentration of scandium increased at both the hot and the cold sides of specimen. Such a distribution is caused by a movement of scandium toward the both ends through the specimen. The movement of scandium toward the cold end is explained qualitatively in terms of the scandium flow associated with vacancy flow. It is pointed out that such an induced solute flow plays an important role on the thermomigration in substitutional alloys, and that the vacancy distribution under a temperature gradient should be investigated quantitatively to establish a well understanding of thermomigration in substitutional alloys.

Vacancy Annihilation to Non-Uniformly Distributed Dislocations in Quenched Aluminum

Annealing profiles of vacancies in zone-refined aluminum were studied by electrical resistance measurement after quenching, and discussed under either assumption of uniform distribution of dislocations or non-uniform one. The annealing curves calculated for the non-uniform distribution of dislocations, using E m 1 =0.65 eV, E m 2 =0.50 eV and B 2 =0.17 eV, show the excellent fit to the experimental annealing curves. It is suggested from such an analysis that the annealing experiment should be made on the specimen with a controlled dislocation density and configuration in order to clarify the fundamental properties of point defects in metals.

Adsorption behavior of sulfur-containing amino acid molecule on transition metal surface studied by S K-edge NEXAFS

Abstract Adsorption behavior of a sulfur-containing amino acid L-cysteine molecule on transition metal surface have been investigated by S K-edge near-edge X-ray absorption fine structure. The L-cysteine molecule for first adsorption layer was found to dissociate on polycrystalline nickel surface, whereas molecularly adsorbed on copper surface at room temperature. Most of the L-cysteine molecules have been dissociated on nickel surface in annealing condition up to 353 K. On the other hand, the L-cysteine molecule did not dissociate on copper surface and the elongation of the S–C bonding occurred at 353 K.

Trehalose Bioprotective Effects in Lysozyme Aqueous Solution Studied by Brillouin Scattering and Calorimetric Measurements

The bioprotective effect of trehalose in lysozyme aqueous solutions has been investigated by Brillouin scattering and modulated-temperature differential scanning calorimetry (MDSC). MDSC experiments show that the isothermal kinetics of thermally irreversible denaturation can be described by the Arrhenius equation. By the addition of trehalose, the irreversible denaturation of lysozyme is suppressed, and its activation energy is half that of the denaturation without trehalose. The sound velocity of lysozyme–trehalose–water ternary solutions obviously depends on the trehalose concentration. With increasing trehalose concentration, the sound velocity becomes higher because the hydration of trehalose reduces the hydrogen bonds between water molecules. Moreover, hydration around lysozyme molecules increases the sound velocity further. Trehalose molecules tend to aggregate with lysozyme molecules at high trehalose concentrations. The bioprotective effect of trehalose probably originates from the mechanical suppression of conformational fluctuations of lysozyme molecules.

Thermal generation of vacancies in high-quality aluminium crystals

Abstract The dislocation density in high-purity (99.9999%) aluminium has been decreased to 105–107 m−2 by cyclic annealing. In such a crystal, there are only a few sources for vacancy generation, so that it is expected to take a long time to attain the thermal equilibrium concentration of vacancies. In order to study the generation rate of vacancies, the electrical resistance has been measured accurately at high temperatures. It is found that it takes at least several hours to attain the thermal equilibrium concentration. For comparison, generation profiles from pre-existing dislocations and interstitial-type dislocation loops are estimated with a diffusion-limited model. It is concluded that, even in a high-quality aluminium crystal, most vacancies are generated from pre-existing dislocations, and only a small fraction is generated by the growth of interstitial-type dislocation loops. The surface oxidizes at a rate of about an atom layer per an hour and is not effective for the generation of vacancies.

Negative Resistance due to the Ballistic Conduction of Electrons in a Metal Single Crystal

Negative resistance has been observed at 4.2 K in a cross-shaped specimen cut from a high-purity aluminum single crystal with a residual resistance ratio of about 100000. The cross section of arms of the specimen was 0.5 mm × 0.4 mm and the bulk mean free path l b of conduction electrons was about 3 mm. The negative resistance was enhanced in a magnetic field parallel to a pair of arms. Nonlinear I - V characteristics were also observed when one of the potential probes was placed on the middle part of an arm at a distance 2 mm (< l b ) from the center of the intersection of the arms. The negative resistance and the nonlinear I - V characteristics were attributed to the ballistic conduction of electrons.

Temperature Dependence of Positron Trapping to Dislocations in Aluminum

Doppler-broadening lineshapes of positron annihilation in high purity aluminum have been measured as a function of temperature between 4.2 and 275 K after deformation and recovery at room temperature. The effective trapping rate exhibits a strongly negative dependence on temperature below 200 K in material of 99.9999% purity, but only below 70 K in 99.999% purity. The results can be explained with a model where positrons become trapped in deep traps ( e.g. , jogs) via shallow traps (dislocation lines) from which thermal detrapping can occur. The temperature dependence of the effective trapping rate found in material of 99.999% purity is attributed to the temperature dependence of the specific trapping rate to the dislocation line.

Anisotropy of Residual Electrical Resistivity in High-Purity Aluminum Single Crystals

Measurements have been made on the residual electrical resistivity in single crystals of high-purity aluminum ( R R R ≃ 50000) at 4.2 K. The samples were cut from single-crystal plates with {110} surfaces. The axes of the samples were oriented parallel with the principal axes , and . The results show strong anisotropy, previously not predicted for a normal metal with cubic symmetry. The resistivity increases in the order of the , and directions; the value along is significantly larger than those of the other two directions.

Clustering Process of Vacancies in Quenched Aluminum

Faulted loops and voids in quenched high purity aluminum were observed with an electron microscope and it was investigated how the quenching rate and the aging temperature affect the formation of faulted loops and voids. The clustering process of vacancues durung the quenching and the aging is simulated by using a model which takes into account vacancy clusters containing up to sixteen vacancies for the formation of faulted loops. Comparing the simulated results with the experimental ones, it is confirmed that the density of faulted loops is determined by the concentration of quenched-in vacancies and does not depend on the clustering process during the quenching in the present experimental circumstances. It is conclucled that the cluster composed of around ten vacancies is the origin of faulted loops in the clustering process at room temperature, because the calculated density of them agrees well with the observed one.

Efficiency of Dislocation as a Sink for Vacancies in Deformed Aluminum

The annealing of vacancies in deformed aluminum was studied by electrical resistance measurements. The remarkable results are summarized as follows (i) decay rate of vacancies decreases with the increase of strain e for the deformation, in spite of the high density of dislocations introduced by the deformation, (ii) the apparent activation energy which was determined by the change of slope method during the annealing becomes larger with the strain, (iii) the jump number of vacancy in deformed specimens has an almost constant value during the annealing for each specimen. These results are explained in terms of the efficiency of dislocation as a sink for vacancies, and it is concluded that the main contribution to the efficiency comes from the line tension of dislocations constrained geometrically.