Ni/YBa sub 2 Cu sub 3 O sub 7 minus sub x and Ni/Bi sub 2 Sr sub 2 Ca sub 0. 8 Y sub 0. 2 Cu sub 2 O sub x interface formation: Reactivity, segregation, and chemical trapping

Interfaces formed by condensing Ni atoms onto YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} (Y-123) and Bi{sub 2}Sr{sub 2}Ca{sub 0.8}Y{sub 0.2}Cu{sub 2}O{sub {ital x}} (Bi-2212) have been studied with x-ray photoelectron spectroscopy. For both Y-123 and Bi-2212, the Ni 2{ital p}{sub 3/2} and O 1{ital s} core level features indicate Ni--O reactions and changes in the Cu 2{ital p}{sub 3/2} emission that reflect reduction from nominal Cu{sup 2+} to Cu{sup 1+} oxidation states. Ni deposition onto Bi-2212 also reduces Bi--O bonding and releases Bi atoms. For Ni/Y-123, analysis of emission intensities as a function of coverage shows that O and Ba intermix in the growing metal overlayer but that Cu is trapped at the buried interface. For Ni/Bi-2212, similar analysis shows O and Bi intermixing but less effective Cu trapping.