Yo Ichikawa

Preparation and Characterization of Superconducting Y–Ba–Cu–O Thin Films

Thin films of Y-Ba-Cu-O system have been prepared by rf-magnetron sputtering technique. The films were crystallized through post annealing and superconductivity was appeared. The film on R-plane of sapphire showed superconducting transition with an onset temperature at 94 K and zero-ρ state was achieved below 70 K.

Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses

Terahertz (THz) radiation generated from photoconductive antenna fabricated on a single crystal zinc oxide (ZnO) is presented. The THz-radiation power is saturated at bias voltages above 800V∕cm and the obtained spectrum extends up to 1 THz. Moreover, ZnO is found to be highly transparent in the visible, near-infrared, mid-infrared and THz frequency regions. The results depicted here will categorically unravel the prospects of using ZnO as a material for integrated active optics.

Diamagnetic Properties of High-Tc Bi-Sr-Ca-Cu-O Superconducting Thin Films

The diamagnetic properties of superconductive Bi-Sr-Ca-Cu oxide thin films were studied, by using an rf SQUID susceptometer. The specimen showing diamagnetization up to about 100 K has also indicated the zero-resistance temperature of 102 K. The critical current density is estimated from the diamagnetization shielding effect to be 3.3×106 A/cm2 at 4.2 K and 7×104 A/cm2 at 77 K.

Thin film processing for high- Tc superconductors of the Bi-system

Basic thin film deposition processes for controlled deposition of the high- T c superconductors of the Bi-systems are described. The layered structures of Bi-oxide superconductors are fabricated by a multitarget sputtering process. The multitarget sputtering process realizes the controlled deposition of single phase Bi-oxide superconductors, Bi 2 O 2 · 2SrO · ( n −1)CaO · n CuO 2 for n = 1 to 5. The minimum thickness controlled by the multitarget sputtering is a half crystal unit-cell of around 15 A, and the superlattices comprising ( A k B k ) · m , where A and B denote the Bi-oxide superconductors with different numbers of Cu–O layers, could be fabricated for k > 1, although ion mixing takes place during the sputtering deposition due to the bombardment of the highly energetic sputtered adatoms. Multitarget sputtering will be available for the fabrication of the artificially-made layered oxide superconductors (ALOS).

Preparation and Properties of Superconducting Bi-Sr-Ca-Cu-O Thin Films

Thin films of the superconducting Bi-Sr-Ca-Cu-O system have been prepared on MgO and SrTiO3 substrates by rf-magnetron sputtering and subsequent heat treatment. The films had preferred orientation and exhibited superconducting transition with zero- ρ temperature of around 70 K. Large resistivity drops at 110 K were observed only when the films were deposited at relatively high substrate temperatures (>600°C) and heat-treated.

Effect of Overcoating with Dielectric Films on the Superconductive Properties of the High-Tc Y-Ba-Cu-O Films

The high-Tc Y-Ba-Cu-O superconductive thin films were coated with dielectric films of Nb2O5 and Al2O3 using an rf-magnetron sputtering technique. The coating with dielectric films lowered the zero-resistance temperature of the Y-Ba-Cu-O films. The Auger analyses for these overcoated Y-Ba-Cu-O films suggested that internal diffusion appeared between the Y-Ba-Cu-O films and the dielectric films. It was also found that the crystallinity of the Y-Ba-Cu-O films was degraded due to the overcoating of the dielectric films.

In Situ Preparation of Pb-Based Superconducting Thin Films at Low Temperature and Low Oxidizing Atmosphere

Thin films of Pb-based superconductor have been epitaxially grown in situ on MgO (100) substrates by rf-magnetron sputtering. The growth temperature was 550°C, which is relatively low compared to that of conventional oxide-superconducting films. The reducing atmosphere was preferable for the formation of films with Pb-3212 structure, and no oxygen was required in the sputtering gas. The film showed a superconductive transition at 75 K, and zero-resistivity was realized below 60 K without post-heat treatment.

Microstructures of sputtered PbTiO3 thin films

Ultrathin stoichiometric PbTiO3 films, 10–100 nm thick, were deposited on (001) SrTiO3 substrate at 600u2009°C by rf planar magnetron sputtering to understand the microstructure of initial film growth. The electron microscopy and x‐ray diffraction analysis suggested epitaxial growth of (001) PbTiO3/(001) SrTiO3 with three‐dimensional crystal orientation; however, the PbTiO3 films still included crystal boundaries. Miscut (001) SrTiO3 substrates reduced the crystal boundaries and provided continuous ultrathin films of single crystal PbTiO3. Rapid thermal annealing at 600u2009°C for 10 s further improved their crystallinity.

Possibility of High Tc Superconducting Thin Films in Magnetic Application

Magnetic properties of BiSrCaCuO and other superconducting oxide films in a technical field region were surveyed from a viewpoint of magnetic application. Permeability, hysteresis loops, magnetic anisotropy and high frequency response were measured in the superconducting region with discussion. These results seem to be well explained by the Bean model in which a number of magnetic fluxoids thread the superconductor. These films will be helpful as soft magnetic materials in a very high frequency region.

80 K Superconductivity in Bi-Sr-Cu-O Thin Films

High-Tc superconductivity near 80 K has been obtained in Bi-Sr-Cu-O thin films. Films were prepared by rf-magnetron sputtering onto heated MgO substrates and heat-treated. It was found that the Bi-based crystal structure with a c-axis length of 3.12 nm was formed in thin film. This film exhibited the superconducting transition with the onset temperature of about 80 K. The present superconducting phase in the Bi-Sr-Cu-O system is considered to be the isostructure with the conventional 80 K Bi2Sr2CaCu2Oy (2-2-1-2) phase.