High Tc Y-Ba-Cu-O Films Prepared by Multilayer, Reactive Sputtering from Separate Y, Cu, and Ba0.5Cu0.5 Targets
In order to thoroughly investigate the phase diagram in films, and to perform destructive tests (e.g. various annealing procedures), a set (nearly ninety) of films having a composition YxBa2CuyOz with 0.6 < x < 1.9 and 2.5 < y < 4.5 (centered around the Y1Ba2Cu3O7-δ compound in the ternary phase diagram) were prepared on MgO. Multilayer deposition of the constituents at ambient temperature was performed by reactive de-maguetron sputtering from separate Y, Cu, and Ba0.5Cu0.5 targets in an atmosphere of 6×10-5 Tarr O2 and 1.0×10-2 Torr Ar. Two hinds of post-deposition heat treatment were applied: rapid thermal annealing between 950–1000°C and slow annealing between 840–860°C. Superconducting films with Tc (R=0) between 80 K and 90 K were routinely produced by the rapid thermal annealing process, if the stoichiometry lay in the range of 0.9 < x < 1.4 and 3.2 < y < 3.5. The interrelation between stoichiometry, heat treatment, Tc (R=0), chemical reactions with the substrate, and the presence of phases; other than the known 1-2-3 superconductor was explored, Raman spectroscopy was employed to study the latter two properties. A stroug correlation was found between the Raman spectra and Tc (R=0), which suggests the potential utility of Raman scattering as an in-situ probe to characterize the growth of Y-Ba-Cu-O films. We also found that the rapid thermal annealing process is a very efficient way to reduce chemical reactions of the film with its substrate.
KeywordsRaman Spectrum Rapid Thermal Annealing Resistive Transition Rapid Thermal Annealing Process Thin Film Superconductor
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