Keizo Harada

Growth of Buffer Layers on Si Substrate for High-Tc Superconducting Thin Films

We have investigated the crystalline properties and surface morphology of the buffer layers of Y2O3, ZrO2 and Y2O3/ZrO2 on a Si(100) substrate for a superconducting thin film. The results of RHEED and X-ray diffraction indicate the hetero-epitaxial growth of buffer layers on Si(100) substrates. Epitaxial planes of the buffer layers on the Si(100) surface are (110), (100) and (100)/(100) for Y2O3, ZrO2 and Y2O3/ZrO2, respectively. YBa2Cu3O7-x thin films have been grown on Si with each buffer layer. The highest critical temperature obtained was 88 K on the Si with the Y2O3/ZrO2 buffer layer.

Y–Ba–Cu–O Thin Film on Si Substrate

Superconducting Y-Ba-Cu-O thin films have been prepared by RF magnetron sputtering on Si(100) substrate with a buffer layer of ZrO2 or MgO. The film with a ZrO2 buffer layer exhibited a superconductive transition with zero resistance at 82 K. X-ray diffraction patterns indicated a preferential orientation where c-axes were perpendicular to the substrate.

Crystal Orientation of YBa2Cu3O7-y Thin Films Prepared by RF Sputtering

The effect of growth temperature on the crystallinity and morphology of YBa2Cu3O7-y thin films was investigated. Thin films were grown on MgO (100) single-crystal substrates by RF magnetron sputtering. Preferred orientations of thin films can be controlled by adjusting the substrate temperature, Ts; (100) a-axis oriented films were deposited at 540°C<Ts<550°C, (110) oriented films were deposited at 565°C<Ts<600°C and (001) c-axis oriented films were deposited above 610°C.

Nickel Substrate Having Three-Dimensional Micronetwork Structure for High-Power Nickel/Metal-Hydride Battery

A low-cost substrate for the positive electrode of nickel/metal-hydride battery was developed by using a nonwoven cloth with a three-dimensional micronetwork structure, in which the amount of plated nickel was less than half compared with the conventional foam-type substrate. The substrate was designed to have a finer structure than the foam-type substrate. The cylindrical sealed cell using the substrate exhibited superior high-rate discharging capability to the cell using the foam-type substrate, despite the reduction of plated nickel. The characteristic microporous structure of the substrate presumably contributes to the improvement of high-rate discharge performance.

Heteroepitaxial Growth of Y–Ba–Cu–O/Bi–Sr–Cu–O/Y–Ba–Cu–O

Heteroepitaxial films of YBa2Cu3O7-x/Bi2Sr2CuOy/YBa2Cu3O7-x have been successfully grown using the in situ process. The RHEED pattern of each layer observed in situ showed streaks. The result of cross-sectional transmission electron micrograph (TEM) observation indicates virtually no disruption at the interfaces with the 6 nm-thick intermediate layer. Temperature dependence of resistance through the trilayer also indicates that there is no disruption which would cause short passes for supercurrent between the top and base superconducting layers.

Influence of Nickel Foam Pore Structure on the High-Rate Capability of Nickel/Metal-Hydride Batteries

The influence of nickel foam pore structure on the high-rate capability of nickel/metal-hydride (Ni/MH) batteries was studied to develop a substrate suitable for high-power use. Three types of nickel foam substrates with different pore structures were used for preparing the sealed cells. Among the three prepared sealed cells, the cell using the substrate with a smallest pore diameter and largest surface area exhibited the best high-rate discharging performance. The electrochemical impedance measurement also showed a close relationship between the charge-transfer resistance and the pore structure of the substrate. The contact area between the current collector and the active material is considered to significantly affect the contact resistance and the charge-transfer resistance. The pore-size reduction and the enlargement of the surface area of the substrate were revealed to be effective in improving the high-rate performance of Ni/MH batteries.

Properties of high Jc BiSrCaCuO and TlBaCaCuO thin film

Abstract BiSrCaCuO thin films were prepared by an RF magnetron sputtering. We obtained a c-axis oriented polycrystal with many intergrowth layers. This film has high Jc of 3.4MA/cm 2 at 77.3K. TlBaCaCuO thin films were also prepared by the sputtering. It was a c-axis textured polycrystalline thin film. Its Tc(R=0) and Jc was 115K and 3.2MA/cm 2 , respectively.

Properties of High Jc BiSrCaCuO Thin Film

BiSrCaCuO thin films were grown on MgO substrate by an RF magnetron sputtering. Its Jc was 1.9 million A/cm2 at 77.3K and 21 million A/cm2 at 40K. Anisotropic degradation of Jc was observed. In the most severe case, Jc decreased to 0.1 million A/cm2 as applied magnetic field increased to only 0.5 Tesla. X-ray analysis showed that this film consists of almost single high Tc 2223 phase with c=37.2A. RHEED, SEM and TEM observation showed that this high Jc thin film was c axis oriented polycrystalline. The grain boundaries and stacking faults were not barriers for supercurrent to flow but they might act as pinning places for magnetic flux.

Resistive Behavior of High Tc Superconducting Thin Film in Magnetic Field

We have measured the temperature dependence of resistance for epitaxial and polycrystalline YBCO thin films in a magnetic field. The resistive behavior of the epitaxial thin film could be explained by the flux creep model. The pinning potential estimated from that model had strong anisotoropy and this anisotropy was consistent with that of the coherence length. On the other hand, the resistive behavior of the polycrystalline thin film could not be explained by the flux creep model. It was suggested that the broadening of the resistivity for the polycrystalline thin film is caused by weakly linked grain boundaries.