Shinichiro Koba

Ultrathin film preparation of superconducting 2223 Bi(Pb)SrCaCuO by sputter deposition and rapid annealing

The growth of superconducting Bi(Pb)SrCaCuO thin films was examined. Films with various thicknesses between 100 - 3000 A were prepared on MgO(100) substrates by sputter deposition and subsequent rapid annealing. The obtained films were c-axis oriented superconducting thin films with a 2223 phase and zero resistivity at 100 - 105 K. The ultrathin film of thickness 200 A showed zero resistivity at 100 K and had a critical current density () of about at 77 K whilst in a zero magnetic field. This film displayed a of at 77 K under a 1 T magnetic field applied parallel to the film surface and perpendicular to the current direction. decreased very slightly in a low magnetic field (0 - 0.1 T) and no hysteresis was observed in the - B curve. The film also showed little degradation of in magnetic fields of up to 3 T.

MgB2 thin film fabrication by rf magnetron sputtering

Abstract Superconducting MgB 2 thin films on MgO substrate were fabricated by rf magnetron sputtering. Sputtering was preformed in a 50 mTorr Ar atmosphere at room temperature using sintered MgB 2 or pure B and a Mg metal target. Sputtering deposition was followed by in situ annealing at 650 °C for 5 min in a high vacuum. The film deposited by a pure B and Mg metal had a superconducting transition temperature of 27 K. On the other hand, sputtering using a sintered target brought on the oxidation of Mg and obstructed the formation of superconducting thin films.

Formation of the Bi2Sr2Can−1CunOx (n=2–4) single phase and phase intergrowth in sputter deposited thin films

Abstract Superconducting Bi 2 Sr 2 Ca n −1 Cu n O x (BSCCO) ( n =2–5) thin films were prepared by sputtering. Phase intergrowth among n =2–3, 3–4 and 4–5 phases was observed. The molar fraction of each phase in the mixed crystal of the deposited films was determined by X-ray diffraction analyses and investigated as a function of O 2 gas pressure during sputtering. We investigated the changes of the superconducting properties by molar fraction of each phase. The fabrication conditions for selective growth of the single n =2, 3 and 4 phases in BSCCO thin film are discussed.

Critical parameters in the sputter-deposition of NdBa2Cu3O7-delta thin films

A superconducting thin film of NdBa2Cu3O7- (NBCO) was prepared on an MgO(100) substrate by dc magnetron sputtering. Superconducting properties as well as features such as resistivity at room temperature and surface morphology were improved by optimizing the composition of sputtering target and critical parameters such as substrate temperature and oxidation gas pressure. A highly c-axis oriented thin film with Tc (zero resistance temperature) = 95.2 K was obtained reproducibly with NdBa2Cu3.2O7- off-stoichiometric target sputtering. Tc = 95.2 K was 8 K higher than that deposited by stoichiometric target sputtering. Critical current density was 1 × 106 A cm-2 at 77 K, and surface roughness was 35 nm.

Micropatterning of NdBa2Cu3O thin films using a KrF excimer laser

The effects of laser irradiation for the micropatterning of NdBa2Cu3O superconducting thin films have been investigated. A mask imaging method with a pulsed KrF excimer laser was used. The surrounding area of the etched region of 100-200 µm in diameter was observed to turn white by SEM observation. The Cu 2p and O 1s photoelectron spectra from this region by XPS clearly differed from the normal region. The zero-resistivity temperature of the NdBa2Cu3O film was decreased from 81 K for before patterning to 72.0 K. This was attributed to the dissociation of O- ions from the films surface by laser irradiation. The optimum energy density for minimizing the influence of oxide thin films was found to be 0.26 J cm-2. Oxygen-controlled annealing after patterning was effective to recover Tc.

Effects of Nd–Ba substitution in sputter deposited Nd1+xBa2−xCu3O (NBCO) thin film

Abstract To obtain smooth NBCO thin films by sputtering, we have investigated the correlation of surface morphology with amounts of Nd–Ba substitution (x). Surface morphology and crystal structure of NBCO thin film were influenced by x. NBCO thin films deposited by optimum conditions showed a Tc of 95.4 K and current density of 10 6 A / cm 2 . AFM observation revealed that the line scan surface roughness was 5.5 nm over an area of 5 μm 2 . A variation of surface morphology by substitution of Nd and Ba ions was discussed.

Superconductivity of SrxCuO2-δ Film in YBCO/SrxCuO2-δ/YBCO System

The zero resistance behavior of a SrxCuO2-δ film (x=0.05 ~ 1.0) sandwiched between YBa2Cu3O7-z film was examined. The highest transition temperatures of the sandwiched-type-SrxCuO2-δ, which was deposited optimally at x=0.1 and with a thickness ≈2200 A, was Tc-end = 93.8 K and Tc-onset = 99.0 K. In the region of x=0.05 ~ 1.0, the scattering order of Tc tended to decrease with increase of x, and the resistivity in a normal state had a minimum value at x=0.1. XRD exhibited a phase transformation of a infinite layer type (at x=1.0)-to-NaCl type like C/2c (at x=0.1). It was determined by XPS that Sr-3d5/2,3/2 core lines were the same value for both concentrations of x=1.0 and 0.1 in SrxCuO2-δ.

Transport properties of SrxCuO2-σ film in YBCO/SrxCuO2-σ/YBCO system

Abstract The zero resistance behavior of a SrxCuO2-σ film sandwiched with YBa2Cu3O7−z films has been examined. The transition temperatures of the sandwiched-type-SrxCuO2-δ, which was deposited optimally at x=0.1 and with thickness ≈2200A, was Tc-end=93.8K and Tc-on=99.0K.

Fabrication and superconductivity of YBCO/CuO/YBCO films

The AC susceptibility of a CuO film sandwiched with YBa2Cu3O7−δ (YBCO) films has been examined. The trilayer films are fabricated on a SrTiO3 substrate by using in-situ DC magnetron sputtering. The superconducting transition of AC susceptibility of the CuO sandwiched with YBCO reached the onset temperature of 94.0K followed by the end of transition at 92.5K. The critical temperature for the zero resistivity of YBCO electrodes in this trilayer sample was 88.1K. The thin CuO layer with the thickness of ∼300Å was speculated to have defects induced with diffusion of Ba from YBCO. The chemical shifts of ∼1eV was observed in the binding energy of Ba3d5/2 from that of both YBCO and BaO by X-ray photoemission spectroscopy.

RAPIDLY ANNEALED Bi(Pb)SrCaCuO THIN FILMS PREPARED BY A 2223 STOICHIOMETRIC TARGET SPUTTERING

Thin films of BiSrCaCuO were prepared on MgO (100) by a single target sputtering. This deposition process yielded c-axis oriented superconducting thin films with a smooth surface. The as-grown films grown at 670–690°C showed 2223 single phase and zero resistivity at about 60 K. The as-grown films were directly placed on a Bi(Pb)SrCaCuO bulk sample, and then rapidly annealed at 835–845°C within 40 s in air. The superconducting properties of the annealed Bi(Pb)SrCaCuO films were greatly improved by optimizing the temperature and time during rapid annealing. Films annealed at 840°C for 30s in air showed zero resistivity at 100 K and had the critital current of about 1×106A/cm2 at 77 K. The surfaces of these films on MgO were black and smooth. The film quality is greatly improved by means of annealing process at 840°C for a very short time of 30 s in air after deposition.