Kazushi Sugawara

Epitaxial growth of Bi‐Sr‐Ca‐Cu‐O superconducting thin films by metalorganic chemical vapor deposition

The epitaxial growth of Bi‐Sr‐Ca‐Cu‐O thin films was achieved by metalorganic chemical vapor deposition. The film‐MgO substrate interface has been examined and discussed using the cross‐sectional transmission electron microscopy. On the smooth surface of the MgO substrate, the lattice of the film was ordered from the first atomic layer on the surface of the substrate, and the misfit dislocations caused by the large lattice mismatch between the film and the MgO substrate appeared every four or five lattices. The first Bi2O2 layer on the substrate surface was found to be regularly arranged regardless of the roughness of the substrate surface. The x‐ray diffraction patterns of the films as a function of the growth time showed that the high Tc phase (Bi2Sr2Ca2Cu3Ox) was not formed in the early stage of the growth while its amount increased as the growth was prolonged. These results suggest that the high Tc phase is not directly grown but formed via the low Tc phase (Bi2Sr2CaCu2Ox) or semiconducting phase (Bi2...

Preparation of ultrathin Bi‐Sr‐Ca‐Cu‐O superconducting films by metalorganic chemical vapor deposition

Ultrathin Bi‐Sr‐Ca‐Cu‐O films close to a single unit cell [c=3.1 nm for Bi2Sr2CaCu2Ox (2212) phase] were grown on a (100)MgO substrate by metalorganic chemical vapor deposition. The ultrathin film, having an average thickness of 3.5 nm, exhibited a zero‐resistance superconducting transition, Tc,0=64 K, comparable with the Tc,0 of much thicker films, whereas the superconducting property of thinner films than 3.5 nm was drastically deteriorated. The x‐ray diffraction (XRD) measurement of the ultrathin films showed that the reflection peaks from 00l contributed to a 2212 phase were observed even in the 2.2‐nm‐thick film, and that its c‐axis lattice constant was consistent with that of a bulk 2212 phase. On the other hand, the thicker films than 5.5 nm mainly consisted of the Bi2Sr2Ca2Cu3Ox (2223) phase with a trace amount of the 2212 phase from the XRD patterns.

The 124 Phase in Y–Ba–Cu–O Films Fabricated by Metalorganic Chemical Vapor Deposition

Y-Ba-Cu-O superconducting films were fabricated on MgO substrates by metalorganic chemical vapor deposition (MOCVD). The experiments were performed at susceptor temperatures between 850°C and 750°C. Efforts were focused on the formation of films containing the so-called 124 superconductor, Y1Ba2Cu4O8. The 124 phase was confirmed by X-ray diffraction to be present in the films fabricated at susceptor temperatures below 800°C. Oxygen partial pressure was found to affect the appearance of the 124 phase.

Preparation and Characterization of Ultrathin BSCCO Films by MOCVD

Ultrathin Bi-Sr-Ca-Cu-O films with high critical transition temperatures were grown on (100) MgO single crystal substrates by MOCVD. The 3.5-nm-thick film close to a single unit cell (3.1 nm) exhibited a complete superconducting resistance transition at 64 K, whereas the superconducting property of much thinner films was drastically deteriorated. From the result of the XRD patterns and SEM observations of ultrathin films, it was found that a 2212 layer was 2-dimensionally grown on the MgO substrate.

Anomalous Behavior of Low Field Microwave Absorption in Ultra-Thin Bi-Sr-Ca-Cu-O Films Fabricated on MgO by MOCVD

Non-resonant microwave absorption (NRMA) has been studied on a 100A thick Bi2Sr2Ca2Cu3Oy film fabricated on an MgO (100) substrate by MOCVD. Temperature dependence of the absorption shape, linewidth and angular dependence between the applied magnetic field and the film surface have been studied.Three different kinds of signals (S1, S2, S3) have been observed below Tc. These signals become maximum at around 55K, 40K and 30K, respectively. The absorption linewidths of Sl and S2 signals increase at temperatures close to Tc (≃65K) and 50K, respectively, a possible indication of vortex interaction.

The Effect of Temperature and Oxygen Partial Pressure on Appearance of 124 Phase in MOCVD Film

Recently, we reported that X-ray diffraction peaks due to the YBa2Cu4O8 phase were detected1), when metal organic chemical vapor deposition (MOCVD) films were fabricated at a susceptor temperature of 800°C by controlling the overall composition within certain limits. In this study, efforts were focused on clarifying the effects of oxygen partial pressure and susceptor temperature on appearance of the 124 phase. The 124 phase existed only in films fabricated at susceptor temperatures below 800°C under oxygen partial pressure of 7.5 torr while the overall composition was controlled within certain limits. Oxygen partial pressure was found to affect the appearance of the 124 phase significantly.

ESR of DPPH as a Probe of Magnetic Flux Fluctuations on the Surface of YBaCuO Made by the MPMG Method

Magnetic flux fluctuations on the surface of Y-Ba-Cu-O samples (powder and bulk), which were made by the MPMG method, were studied by means of ESR of DPPH coated on these samples. The temperature dependence of the ESR linewidth, ΔHpp, and the effect of applied magnetic field on the ΔHpp were studied. ΔHpp gradually increases with decreasing temperature below Tc for all the samples. Analyses revealed that the excess ESR linewidth, δ (ΔHpp)=ΔHpp(T)−Δ Hpp(T≃Tc), is nearly proportional to (1 − T/Tc)a with a≃1.4 at temperatures between about 80K and 89K (≃Tc). It is also found that ΔHpp is broadened by applied magnetic field.