Papers by Author: Hideki Yoshikawa

Abstract: We synthesized Ca-rich Bi-based superconducting whiskers by an Al2O3-seeded glassy quenched platelet method. The grown whiskers were precisely characterized by synchrotron radiation X-ray photoemission spectroscopy and high-resolution transmission electron microscopy. The Ca-rich Bi-based superconducting whiskers show a high critical current density of 2×105A/cm2 at 40K in self-field. We found that excess Ca2+ ions substitute for the Sr2+ sites and cause nano crystalline domains with shorter-period modulation embedded in the base crystalline. The embedded nano crystalline domains can result in structural distorted defects which work as strong pinning center.

Abstract: (Mg,Zn)O films were grown on Zn- and O-face ZnO single crystal substrates by pulsed laser deposition. The surface morphologies of the films grown on the Zn- and O-face substrates were quite different, indicating that no domain inversion occurred in both films. The films showed markedly different features for valence band spectra obtained by hard X-ray photoemission spectroscopy. This suggests that the effect of film polarity should be considered in X-ray photoemission spectroscopy.

Abstract: We deposited Bi2Sr2Ca1Cu2Oy (Bi-2212) superconducting thin films on MgO substrates with or without Al2O3 particles by the rf magnetron sputtering method. From the results, we found that optimum target-substrate distance, rf powers and substrate temperature for obtaining the Bi-2212 films on the MgO substrates were 5mm, 150W and 830°C, respectively. The Bi-2212 films were Bi-2212 single-phase and had the Tc of about 54K . The particle size and the distribution density of Al2O3 were controlled by annealing temperature. The Bi-2212/Al2O3/MgO film showed Bi-2212 single-phase, whereas did not show zero-resistance.