Atomic resolution STM observation of the Bi---O surface of yttrium substituted Bi2Sr2CaCu2Oy single crystals

We first examined Bi---O surfaces of Bi₂Sr₂CaCu₂O_y single crystals, whose Ca sites were substituted by Y ions, using an ultra-high vacuum scanning 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 random distribution of the Y ions.