Kumiko Hirochi

Low‐temperature process for the preparation of high Tc superconducting thin films

We have established the low‐temperature process for the preparation of high Tc superconducting films by rf magnetron sputtering. The films were deposited at a temperature (650 °C) lower than the tetragonal‐orthorhombic transition point with sufficient crystallizing and oxidizing conditions. The as‐deposited Er‐Ba‐Cu‐O film on MgO exhibited a sharp superconductive transition with zero resistance at 86 K. This process prevented diffusion at the film and substrate interface and reduced the porous structure in the films.

Highly oriented superconducting Tl‐Ca‐Ba‐Cu oxide thin films with 2‐1‐2‐2 phase

Thin films of the Tl‐Ca‐Ba‐Cu‐O system with 2‐1‐2‐2 phase have been prepared stably on MgO substrates by rf magnetron sputtering and post‐annealing. The post‐annealing of the films was carefully carried out in order to reduce the effect of evaporation of Tl. The annealed films showed a c‐axis‐oriented structure perpendicular to the substrates. The highest zero‐resistance temperature of the films was 102 K. The highest critical current density obtained so far was 1.2×105 A/cm2 at 77 K.

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.

Pt‐coated substrate effect on oxide superconductive films in low‐temperature processing

Excellent films of a high Tc oxide superconductor were easily produced on Pt‐coated substrates at 650 °C. The film superconductivity was significantly improved by the Pt buffer layer. The c axis of the superconductive film was preferentially oriented perpendicularly to the plane with the crystalline oriented Pt coating layer.

Electrical measurements in high Tc Bi‐Sr‐Ca‐Cu‐O thin films

Electrical measurements were performed on polycrystalline thin films of the high Tc Bi‐Sr‐Ca‐Cu‐O system. The resistance of the superconducting state was confirmed to be smaller than 10−8 Ω cm at 100 K. It is confirmed directly that the critical current density at 77 K was in excess of 105 A/cm2 and the dependence of critical current on temperature was able to be represented approximately by (1−T/Tc )2.

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.

Electrical measurements in high T/sub c/ Bi-Sr-Ca-Cu-O thin films

Electrical measurements were performed on polycrystalline thin films of the high Tc Bi‐Sr‐Ca‐Cu‐O system. The resistance of the superconducting state was confirmed to be smaller than 10−8 Ω cm at 100 K. It is confirmed directly that the critical current density at 77 K was in excess of 105 A/cm2 and the dependence of critical current on temperature was able to be represented approximately by (1−T/Tc )2.

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).

Optical properties of Nd2−xCexCuO4 thin films

Abstract The normal-state optical reflectivity and absorption spectra of the Nd 2−x Ce x CuO 4 system with various Ce concentrations from x =0 to 0.18 have been measured for the first time using highly oriented thin films with c-axis normal to (100) SrTiO 3 substrates. The absorption spectra of x =0 indicated the existence of the interband transition with the band gap of 1.3 eV in the undoped Nd 2 CuO 4 . When Ce ions were doped, the interband transition was suppressed and the broad absorption below 1 eV came to be seen. In the reflectivity spectra for x≥0.12 films, a metallic plasma reflection due to the free-carriers was observed. Based on the Drude model, the plasma frequency ℏ ω p =1.07 eV was obtained for the superconducting compositional region, 0.14≤x≤0.18.

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.