Hideto Adachi

Superconducting (Sr, Nd) CuOy thin films with infinite-layer structure

Abstract Thin films with infinite-layer structure have been prepared using a magnetron sputtering system and the substitution of neodymium for strontium in SrCuO 2 has been successfully carried out, which is similar to the case of the high-pressure synthesis. (Sr, Nd)CuO y films were grown in a reducing atmosphere on SrTiO 3 single crystals and epitaxial growth with [001] orientation normal to the substrate was realized at the substrate temperature of 550–600°C. Superconducting transition was observed for some as-grown films, and the Sr 0.88 Nd 0.12 CuO y film showed the highest T c of 16 K.

Superconducting properties of Bi2Sr2CaCu2Oy/Bi2Sr2CuOx multilayer thin films

Abstract We have prepared Bi 2 Sr 2 CaCu 2 O y (BSCCO)/Bi 2 Sr 2 CuO x (BSCO) multilayer thin films using a multitarget RF magnetron sputtering technique. Our BSCO films exhibit a semiconductor-like transport property, and BSCCO/BSCO multilayers are supposed as superconductor/nonsuperconductor multilayers. The x-ray diffraction measurements showed that all of the multilayers with various thicknesses have the c-axis normal to the substrate surface. In the multilayer films with the constant BSCO layer thickness of 100A, an T c onset slightly decreases from 85 K to 75 K with decreasing the BSCCO layer thickness from 250A to 31A. From this result it seems that interlayer coupling in BSCCO/BSCO multilayers is weaker than in YBaCuO/PrBaCuO multilayers.

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.

Superconducting (Nd,Ce)/sub 2/CuO/sub 4/ thin films grown by rf magnetron sputtering

Thin films of an electron‐doped‐type (Nd,Ce)2CuO4 system have been prepared by rf magnetron sputtering and subsequent annealing. The films showed a highly oriented structure with the c axis normal to the film plane. They exhibited superconductivity after the reducing treatment by heating at 800–900 °C in vacuum. The resistivity of the films was fairly low with metallic characteristics, and the sign of the Hall coefficient was negative in the normal state. The sharp superconducting transition with zero resistivity at 22 K was observed for the film of Nd/Ce/Cu:1.855/0.145/1.2.

Incorporation of carbon into infinite-layer BaCuO2 films and formation of superconducting phase

Abstract We have investigated the incorporation of carbon into infinite-layer BaCuO2 films using a sputtering method. When carbon was doped, the films showed a modulated structure with 2c and 3c periodicity along the c-axis of the BaCuO2, indicating that the carbon-incorporated layers are ordered. Transmission-electron-microscopy observation suggested that the “2c” and the “3c” structures were isomorphous with the 1201 (endmember) and 1212 phases of homologous (C,Cu)Ba2Can−1CunOx, respectively. The “2c” modulated film exhibited a superconducting transition around 40–50 K.

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.

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.

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.

Low-noise 650-nm-band AlGaInP visible laser diodes with a highly doped saturable absorbing layer

Stable self-sustained pulsating and low-noise 650-nm-band AlGaInP visible laser diodes were demonstrated by adopting a novel structure, which has a highly doped saturable absorbing (SA) layer. Short carrier lifetime, which is indispensable for self-pulsation, was realized by applying high doping concentration to the p-type SA layer. 500-/spl mu/m-long devices with 51%/51% coated facets were fabricated, resulting in the threshold current of 75 mA at 20/spl deg/C. The temporal output power was measured at the average output power of 5 mW and the stable self-pulsation was observed up to an ambient temperature of 60/spl deg/C. Therefore, the relative intensity noise (RIN) was kept about -140 dB/Hz in temperature ranging from 20/spl deg/C to 60/spl deg/C. Since the refractive index difference could be kept large and the optical mode could be confined effectively, the astigmatism in this work was below 3 /spl mu/m at 5 mW against dc injection current. The lasers operated over 1350 h under the average output power of 5 mW at 60/spl deg/C.

Epitaxial Y‐Ba‐Cu‐O thin films prepared by rf‐magnetron sputtering

Superconducting Y‐Ba‐Cu‐O thin films were prepared by a rf‐magnetron sputtering process. The preparation conditions, film crystallinity, and resistivity were investigated. The composition of the films strongly depended on the oxygen partial pressure of the sputtering gas. It was found that the substrate temperature during sputtering and the selection of substrate materials governed the crystallinity of the Y‐Ba‐Cu‐O thin films. The preferential c‐axis orientation was obtained for the films prepared on (0112) sapphire, (100) MgO, and (100) SrTiO3 substrates at a substrate temperature of about 750 °C. These as‐deposited films have shown the superconducting transitions which were improved by setting the optimum conditions for sputtering and subsequent anneal process.