Shuji Yazu

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.

YBa2Cu3O7-x Thin Film Prepared by Laser Ablation

High critical current density YBa2Cu3O7-x thin films on (100)SrTiO3 were successfully prepared by laser ablation. The zero resistance transition temperature (Tc(R=0)) was 90.5 K and the critical current density (Jc) at 77.3 K was 8.0×106 A/cm2 under a zero magnetic field. Jc degraded to 1.7×104 A/cm2 in a magnetic field of 8 T parallel to the c-axis of the film, and to 4.0×105 A/cm2 in a magnetic field of 8 T perpendicular to the c-axis of the film. The characteristics of the film, mis-oriented crystallites and stacking faults, were revealed by transmission electron microscopy (TEM).

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.

Synthetic diamond as a pressure generator

Synthetic diamond crystals were used as opposed anvils whose small culet surfaces were driven into contact with each other to generate high static pressures. Pressures in excess of 68 gigapascals (680 kilobars) were achieved, as determined from the fluorescence line of a ruby fragment sandwiched between the diamonds.

Tool Application of Diamond and CBN

Abstract As diamond and cBN have extreme hardness and excellent thermal conductivity, these materials are highly suited for cutting tool applications. Diamond can be used for cutting non-ferrous metal and non-metal such as FRP and ceramic, it is not effective in cutting ferrous metal due to its high affinity to this metal. CBN is a superior material to cutting ferrous metal. This paper reviews the cutting performances of polycrystalline diamond and cBN tools

Further study of the difference in nitrogen aggregation among (111) and (100) growth sectors of synthetic diamonds

Abstract Single nitrogen atoms in synthetic diamond crystals aggregate in pairs by heat treatment under high pressure after electron irradiations. We find that the rate constants of nitrogen aggregation in the (111) growth sectors grown by the various solvents are about ten times greater than those of the (100) growth sectors. Furthermore the rate constant of nitrogen aggregation of the same sector is almost the same value. (shown Table-1). We have considered a few reasons for this fact. It may be accurate that a form of nitrogen atoms contained in (111) growth sectors of an as-grown diamond differs from that in (100) grown sectors and that the former accelerates nitrogen aggregation. Consequently we propose one nitrogen migration and aggregation model.

Optical properties and laser action of H3 center in synthetic diamond

Color centers in diamond have a potential for opto-electronic applications. Laser action of H3 centers in natural diamond has been already reported. Our interest is focused on the possibility of laser action using synthetic diamond. A first attempt was made to produce H3 centers with high density in synthetic diamond. Optical properties of the H3 centers were investigated. Sample-dependent luminescence decay time and long lived transient absorption were observed. Laser action using the H3 centers in synthetic diamond occurred though the efficiency was as low as 0.1%.

Structure of High-Tc Superconducting Thin Film by Laser Ablation

High quality YBa2Cu3O7−x thin films were prepared on (100)SrTiO3 substrate by laser ablation. One of the best samples showed the critical current density (Jc) of 8.0x106A/cm2 at 77.3K under a zero magnetic field. The characteristics of this sample were investigated in comparison with the sample which has Jc of 2.0x106A/cm2. The characteristics of the film, mis-oriented crystallites and stacking faults, were revealed by transmission electron microscopy (TEM). Furthermore, the preferential orientations of the film with various preparation conditions by laser ablation were also studied.