Masayoshi Asahi

Segregated microstructure in sputtered Co‐Cr film revealed by selective wet etching

The segregated microstructure in a sputtered Co‐18.1 at. % Cr film is examined. Thin foil samples are prepared for transmission electron microscopy using selective wet etching and ion‐beam milling. The microstructure revealed by selective wet etching shows a definite striped pattern in each crystallite where the stripes run almost perpendicular to grain boundaries. Results of compositional analysis by an energy dispersive x‐ray microanalyzer reveal that these stripes are caused by dissolution of the Co‐rich ferromagnetic regions and that the remaining regions are Cr‐rich and nonmagnetic. The results are explained by a new model for segregated microstructure formation. Ferromagnetic Co‐rich regions are formed coherently in each single‐phase hcp crystallite, with a wall‐like structure perpendicular to the substrate plane. The observed microstructure suggests the existence of a magnetic unit far smaller than the crystallite diameter, which offers superior properties for high‐density perpendicular magnetic re...

TEM Observation of Microstructure in Sputtered Co-Cr Film

TEM observation of the microstructure in a sputtered Co-18.1 at%Cr film with perpendicular magnetic anisotropy was conducted. The TEM thin foil samples were prepared by dipping them in hydrazine monohydrate solution and milling them with ion beams. It was found that the microstructure of each crystallite showed bright stripe-like features in fairly regular directional patterns, which seemed to reflect compositional inhomogeneity.

TEM Observation of Segregated Microstructure in Sputtered Co?Cr Film

TEM observation of the segregated microstructure in sputtered Co–Cr films was conducted. The specific segregated microstructure was observed in the film composition range of 15.3–24.3 at%Cr–Co. The results present a new model for the origin of the segregation where two-phase separation into magnetic and non-magnetic phases occurs in a single hcp phase. The ferromagnetic Co-rich regions in a crystallite are supposed to be embedded in nonmagnetic Cr-rich matrix, with a wall-like figure perpendicular to the substrate plane.

Superconducting and Structural Properties of EuBa2Cu3O7-δ Ultrathin Films Deposited on MgO(100) Substrates Using Magnetron Sputtering

EuBa2Cu3O7-δ thin films were produced on MgO(100) substrates at 580°C using planar-type magnetron sputtering and were studied by X-ray diffraction and RHEED. The c-oriented films were epitaxially grown with a crystal orientation of [110]EuBaCuO//[010]MgO. Films more than 1000 A thick exhibited Tc endpoints of ~90 K. As film thickness decreased, superconducting properties deteriorated. However, even films with 2-unit-cell thickness became superconducting. The cause of the deterioration of superconducting properties in ultrathin films is discussed on the basis of the relationship between lattice matching and structural properties.

Epitaxy and orientation of Eu1Ba2Cu3O7−y films grown in situ by magnetron sputtering

Superconducting films of Eu1Ba2Cu3O7-y have been grown in situ onto SrTiO3 and MgO (100) substrates by magnetron sputtering from a stoichiometric oxide target. The sputtering process results in the growth of epitaxial films with perfect a-axis orientation as well as perfect c-axis orientation. The orientation of the films can be controlled by the proper choices of substrate temperature, oxygen pressure, and film growth rate. The routine production of films showing Tc zero of 88–90 K is accomplished. In situ growth of the films with the particular orientation is of importance in the fabrication of multilayer structures such as tunnel junctions.

YBaCuO Epitaxial Film Formation by Magnetron Sputtering with Facing Targets : I. Effects of Target and Substrate Positions

YBa2Cu3O7-δ (YBCO) thin films were prepared on non-rotating MgO(100) substrates at 630°C using dc magnetron sputtering with facing targets (dc-MSFT) and the influence of target and substrate positions on film characteristics, such as superconducting properties, composition (CCu/Y, CBa/Y), crystallinity and uniformity was investigated. Spatial positions at which as-grown epitaxial films with Tce=90 K were deposited were consequently found. Away from the center position, the composition of thin film deviated from a stoichiometric composition, that is, both CCu/Y and CBa/Y had a tendency to decrease. As-grown films with of Tce over 88 K were obtained in a 5×5 cm2 area of the substrate. The deposition rate was about 20 A/min at the center position and decreased by 22% at a position 2.5 cm away from the center.

Epitaxial Growth of SrxTiOy and Fabrication of EuBa2Cu3O7-δ/SrxTiOy/Pb Tunnel Junctions

Thin films deposited from a SrTiO3 (STO) target using rf magnetron sputtering were examined. The Sr1.6TiOy films with perovskitelike structure grew epitaxially at substrate temperatures above 500°C. The trilayered films of EuBa2Cu3O7(EBCO)/STO/EBCO were deposited eptaxially on STO(110) substrates, but partial polycrystal growth in the EBCO film of the third layer was observed. In view of this result, EBCO(110)/STO(110)/Pb tunnel junctions were produced on STO(110) substrates. The I-V characteristics of junctions with an Rnn of 10 Ω showed a gap opening at a bias voltage of about 10 mV, a clear gap structure at 2.5 mV and Rj/Rnn=12.4 below 2.5 mV. The low-energy gap below 2.5 mV was caused by the deterioration of the EBCO base electrodes due to the junction fabrication process. The large Rj/Rnn suggests that an STO epitaxial ultrathin film can be a good low-leakage barrier. On the other hand, lower resistance junctions showed the development of a supercurrent at zero bias.

As-grown Y-Ba-Cu-O superconducting thin films prepared by magnetron sputtering

YBa2Cu3O7-δ thin films were prepared on MgO(001) planes at 600°C by RF magnetron sputtering. These as-grown films were classified into 3 types: high-Tc, low-Tc and nonsuperconducting. In this report, film properties are discussed in relation to the annealing effect in an oxygen atomosphere and lattice parameters (co). By optimizing the sputtering conditions, c-axis-oriented superconducting films with an endpoint Tc above 80 K are obtained. These as-grown films are highly uniform and semi-transparent and have a room temperature resistivity of 0.3 mΩcm.

Dependence of Superconducting Properties on Substrate Temperature in Y–Ba–Cu–O Thin Films Prepared by Magnetron Sputtering

Y-Ba-Cu-O thin films (1500–2000A) are prepared on MgO (001) substrates at 450°C to 680°C by RF magnetron sputtering. At substrate temperatures of 580°C and above, as-grown superconducting films with high c-axis orientation, end-point Tc above 80 K and a smooth surface are obtained. As the substrate temperature decreases below 580°C, transition temperature and diffraction intensity are rapidly reduced, as is the formation of c-axis-oriented crystals with different lattice parameters.

Low-Temperature Growth of High-Tc Bi-Sr-Ca-Cu-O Films by Magnetron Sputtering

Superconducting thin films of Bi-Sr-Ca-Cu-O have been grown on heated MgO, sapphire, and SrTiO3 substrates by magnetron sputtering. For films grown at substrate temperatures between 560–600°C, Tc onset behavior above 110 K was observed. These films contain a phase having a c-axis lattice parameter, c0, of 36.83 A in coexistence with a phase having c0 of 30.67 A. These as-grown films show zero resistence at 56 K. Zero resistence of 90 K was achieved in postannealed films on MgO. A thin-film growth method like sputtering is capable of stabilizing the 110 K phase in the Bi-Sr-Ca-Cu-O system at low growth temperatures below 600°C.