ATOMIC-RESOLUTION STM OBSERVATION OF THE BI-O SURFACE OF YTTRIUM SUBSTITUTED BI2SR2CACU2OY SINGLE-CRYSTALS

We first examined Bi-O surfaces of Bi2Sr2CaCu2Oy single crystals, whos e Ca sites were substituted by Y ions, using an ultra-high vacuum scan ning tunneling microscope (UHV-STM). Atomic resolution surface images were obtained for both the unsubstituted superconducting crystals and non-superconducting crystals, whose 60% Ca sites were substituted by Y ions. We found a lot of unperiodic disorder in the surface structure of the Y substituted crystal. The disorder seems to be caused by the r andom distribution of the Y ions.