Passivation of high T c superconductor surfaces with CaF2 and Bi, Al, and Si oxides

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Abstract
X‐ray photoelectron spectroscopy has been used to investigate passivation of the high‐temperature superconductors YBa2Cu3O7−x and Bi2Ca1+xSr2−xCu2O8+y involving overlayer materials deposited in vacuum onto freshly cleaved surfaces. CaF2 was found to be completely inert and to form uniform overlayers on the surface. Deposition of Bi, Si, and Al in activated oxygen produced oxides and exhibited minimal reaction and disruption of the superconductor surface. In contrast, results for Bi, Si, and Al deposition in nonactivated oxygen or ultrahigh vacuum showed extensive substrate disruption due to surface reactions and oxygen withdrawal. This indicates that the activation technique provides oxygen from the gas phase for oxide formation and facilitates nondisruptive overlayer growth, even for reactive metals.