Electron tunneling microscopy: A direct probe of metal substitution in BiSrCaCuO superconductors

Scanning tunneling microscopy (STM) exploits the extreme distance sensitivity of electron tunneling to achieve atomic resolution imaging of surfaces. The ability of STM to probe directly materials on the atomic scale has been exploited to elucidate the structural effects of metal substitution in the copper oxide superconductor Bi₂Sr₂CuO₆. A series of Bi₂Sr₂CuO₆ single crystals containing lead substituted in the bismuth-oxide layer have been prepared, and the structures of these materials have been characterized by STM. The measurements show that lead-substitution induces complex changes in the structural order of the parent compound. Comparisons of these data with electron diffraction measurements highlight the importance of local crystallography, which STM provides, in studying the chemistry of inorganic materials.