Zon Mori

Two-step in situ annealing effects on sputter-deposited MgB2 thin films

We have investigated the effects of in situ annealing on the superconducting properties of MgB2 thin films for the purpose of obtaining high critical temperature close to bulk value. MgB2 thin films were fabricated by rf magnetron sputtering on C-plane sapphire (Al2O3) substrate. Thin films were produced by simultaneously sputtering pure B and a Mg metal target. Sputtering deposition was followed by in situ annealing in a high vacuum. To prevent the evaporation of Mg from the film surface, two-step annealing was adopted: the first step is the crystallization stage at low-temperature annealing and the next is an improvement of the films superconducting properties by annealing at a high temperature. In the optimal annealing process (a thin film is first heated at 600 ?C for 2 h and then 650 ?C for 2 h) we have consistently obtained thin films with a zero resistivity temperature of 29 K.

Optimal annealing conditions for Y1Ba2Cu3O7-δ thin films

The superconducting current density, Jc, of Y1Ba2Cu3O7−δ (YBCO) is greatly influenced by hole doping levels. Hole doping is mainly dominated by oxygen ordering, so the postannealing process is one of the essential factors for practical applications of YBCO superconductors. However, little research has been reported about the variation in Jc by annealing time. In this study, the optimal annealing conditions were studied using homogeneous c-axis oriented YBCO thin films prepared by the pulsed laser deposition method. As a result, Jc (at 77 K, 0 T) increased from 0.3 to 5.3 MA/cm2 with an annealing time in the range of 0–12 h. This result suggests that annealing for tens of hours is essential for obtaining high Jc samples, even if the film is 250 nm thick. The oxygen diffusion process was examined by applying the one-dimensional diffusion model.

Flux Pinning Properties of Multilayered

In this paper, we will show the superconducting properties of the alternately-layered MgB2/Ni thin films. MgB2/Ni multilayered thin films were prepared on silicon substrates (100) by sequentially switching an electron beam evaporation technique and a coaxial vacuum arc evaporation source. The lattice spacing of artificial pinning layers was designed to correspond to a magnetic field of 8 T (flux line lattice spacing of 15 nm). As a result, clear enhancement of Jc was observed in the multilayered thin film when the fields applied parallel to the film surface. The results suggest a great possibility of the artificial nanostructure to improve superconducting performances of MgB2.

{\rm MgB}_{2}/{\rm Ni}

Optimizing oxygen content is one of the most essential factors with practical ramifications for the production of Y1Ba2Cu3O7–δ (YBCO) superconductors. In this study, oxygen diffusion was studied using homogeneous c-axis oriented YBCO thin films prepared via the pulsed laser deposition method. The oxygen diffusion process was examined by applying the one-dimensional diffusion model. The diffusion coefficient of oxygen and the activation energy were determined. This will facilitate the optimization of oxygenation in the production of thin films for YBCO superconductors.

Thin Films

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.

Oxygen diffusion in c-axis oriented Y1Ba2Cu3O7−δ 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.

MgB2 thin film fabrication by rf magnetron sputtering

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.

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

In this paper, we prepared alternately layered MgB₂/B examine the superconducting properties of multilayered MgB₂ thin films prepared inserting a very thin layer of boron between MgB₂ . The multilayered MgB_2/B thin films were prepared successfully using electron beam evaporation technique without any post-annealing. No inter-diffusion of magnesium and boron can be detected in the multilayered thin films consist of individual MgB₂ and boron layers.

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

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.

Multilayered

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.