Kou Takeuchi

Preparation of High-Tc Bi-Sr-Ca-Cu-O Superconducting Thin Films by AC Sputtering

Thin films of Bi-Sr-Ca-Cu-O superconductors were prepared on a polycrystalline YSZ substrate by the 50 Hz ac sputtering method. A pair of targets with various compositions were used in this apparatus. The films deposited without intentional heating were amorphous insulators. When the films were annealed at temperatures ranging from 750°C to 900°C, X-ray diffraction analysis showed that they had highly oriented periodic superstructures with various planar spacings. A specimen annealed at 800°C for 120 min has Tc(onset) and Tc(zero resistive) of 115 K and 73 K, respectively.

Reversible Resistivity Control of Ba2YCu3O7-δ Thin Films by Laser Annealing

Laser annealing of superconducting Ba2YCu3O7-δ (BYCO) thin films has been investigated by using a Nd:YAG cw laser. By laser irradiation at power densities higher than 1.4×105 W/cm2, superconducting polycrystalline films became amorphous and showed semiconductor-like temperature dependence on resistivity. The amorphization is apparently caused by a rapid quenching of molten BYCO after laser irradiation. The superconductivity of the film could be recovered by annealing the laser-irradiated film in a furnace. With this mask-free laser irradiation process, patterning of superconducting films can be achieved.

Communication between the right pulmonary artery and left atrium with aneurysm formation

Communication between the pulmonary artery and the left atrium is a rare congenital anomaly. A 7-year-old boy was referred to our hospital with a diagnosis of pulmonary arteriovenous fistula. Referral to a pediatric cardiologist had been delayed because he had only slight cyanosis and no heart murmur. Catheterization and computed tomography scans confirmed that the right pulmonary branches and pulmonary venous returns were normal and that an additional aneurysmal communication was located between the right pulmonary artery and the left atrium. Surgery proceeded uneventfully together with a cardiopulmonary bypass. The connection from the right pulmonary artery to the aneurysm was ligated, and the connection from the left atrium to the aneurysm was closed with a polytetrafluoroethylene patch. We describe this rare anomaly with cyanosis and no heart murmur.

Oxygen Control in Bi2Sr2Ca1Cu2Ox Superconducting Thin Films by Activated Oxygens

Activated oxygens were generated by various methods to compare their effect on the control of oxygen stoichiometry in Bi2Sr2Ca1Cu2Ox superconducting thin films. The treatment of a film with an oxygen plasma or ozone at 400°C decreased the Tc onset of the film by as much as 20 K from untreated film as it was in the case of film treatment in atmospheric oxygen under UV light irradiation. On the other hand, films exposed to UV light irradiation in the presence of N2O (400 Torr) increased their Tc onset to 100 K by about 20 K. These Tc changes accompanied the change in the c-axis lattice constant. The lattice of the specimens with Tc onset of 60 K was smaller than that of the untreated films, while the specimens with Tc onset of about 100 K had a stretched c-lattice. Thus, the oxygen content or hole concentration in Bi2Sr2Ca1Cu2Ox films can be controlled at a relatively low temperature and its effect is reflected in the changes of lattice constant and Tc.

Reversible Tc Change in Bi-Sr-Ca-Cu-O Thin Films by UV Photo and Thermal Annealings

UV light irradiation in oxygen atmosphere was found to cause a change of critical temperature in Bi-Sr-Ca-Cu-O thin films. The change was observed to be reversible between 80 K after thermal annealing and 60 K after photo irradiation. It accompanied a change in the lattice constant, suggesting that further oxygen incorporation into the 80 K phase thin films occurred by the UV light irradiation.

Fluorine doping and superconductivity of Nd2CuO4 thin films

Fluorine was doped into sputter-deposited Nd2CuO4 films to induce superconductivity in the films. The films annealed in the presence of NF3 gas were observed to show remarkable resistivity change which was in parallel with the change of a-axis length. Fluorine incorporation in the films was verified by the X-ray photoelectron spectroscopy analysis. The specimen annealed at 800°C in 0.1 Torr NF3(1%)/Ar gas under UV light irradiation exhibited the onset of superconductivity at 27 K after a reducing procedure at 700°C in Ar.