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  • 1985-1989  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    In situ formation of YBa2Cu3Ox thin films by physical sputtering (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1163-1165 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have found that in situ superconducting Y-Ba-Cu-O thin films can be produced by sputtering without the aid of any external O2 source during deposition. The films were produced by rf magnetron sputtering from a composite target onto MgO(100) substrates heated at 650 °C. Films made in a pure Ar pressure of 24 mTorr and fast cooled in N2 ambient contain the tetragonal YBa2Cu3Ox phase with x estimated to be 6.1. Films made under the same sputtering conditions but cooled in 30 mTorr oxygen after deposition, show a superconducting transition Tc(R=0) at 71 K with an onset at 85 K. The Tc(R=0) rises to 80 K if 0.5 mTorr oxygen was added during sputtering. The experimental results provide conclusive evidence that sufficient oxygen can be incorporated into the films to form the tetragonal YBa2Cu3Ox phase simply by physical sputtering from an oxide target. The films absorb additional oxygen and transform into the orthogonal, superconducting phase when subsequently cooled in partial O2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101560
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Y-Ba-Cu-O films by rf magnetron sputtering using single composite targets: Superconducting and structural properties (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 1735-1737 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High Tc superconducting Y-Ba-Cu-O films have been produced by rf magnetron sputtering using single unreacted composite targets of Y2O3, BaF2, and CuO powders. Transport measurements of the films showed a sharp resistive Tc (R=0) at 89 K and a metallic behavior of resistivity versus temperature. The films show preferred orientations when deposited on single-crystal SrTiO3 substrates (100) or (110) and followed by a post O2 annealing at 825 °C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99716
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Cu valence and the formation of high Tc superconductor oxides studied by x-ray photoemission spectroscopy on 200 A(ring) Bi-Sr-Ca-Cu oxide thin films (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 377-379 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used x-ray photoemission spectroscopy to study the core level spectra of 200 A(ring) Bi-Sr-Ca-Cu oxide thin films, in the hope that the importance of the surface sensitivity of photoemission is minimized for these samples, whose thickness is only 6–7 unit cells. The samples were annealed in oxygen at temperatures ranging from 600 to 870 °C, over which temperature range the thin films are converted from an amorphous insulating phase to an ordered superconducting phase with Tc (R=0)=80 K. Regardless of the annealing temperature, the Cu 2p spectra of all films show satellite structure indicative of Cu2+ states. Even the spectrum of an as-deposited film has a satellite similar to those observed for the annealed films, including the superconducting film. The similarity of the satellite structure in the core level spectra for all films suggests that the Cu-O interactions, such as the Cu d-O p orbital charge transfer energies and the hopping integrals, remain similar when the oxides undergo the insulator-superconductor transition through high-temperature anneal. That is, the same local Cu-O interaction exists before and after the superconducting phase sets in. This implies that the Cu valence alone does not determine the properties of high Tc superconductors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100971
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    Paper (German National Licenses)
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