Scanning Tunneling Microscopy of the Cleaved Surfaces of Bi-Containing Superconductors
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ng Microscopy of the Cleaved Surfaces of BiContaining Superconductors S. L. Tang, R. V. Kasowski, M. A. Subramanian, E. M. Mccarron and W. Y. Hsu MRS Proceedings / Volume 139 / 1989 DOI: 10.1557/PROC139169
Link to this article: http://journals.cambridge.org/ abstract_S1946427400423201 How to cite this article: S. L. Tang, R. V. Kasowski, M. A. Subramanian, E. M. Mccarron and W. Y. Hsu (1989). Scanning Tunneling Microscopy of the Cleaved Surfaces of Bi Containing Superconductors. MRS Proceedings,139, 169 doi:10.1557/ PROC139169 Request Permissions : Click here
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SCANNING TUNNELING MICROSCOPY OF THE CLEAVED SURFACES OF BI-CONTAINING SUPERCONDUCTORS S. L.TANG, R. V.KASOWSKI, M.A.SUBRAMANIAN, E. M. MCCARRON AND W. Y. HSU E. I.du Pont de Nemours &Co., Experimental Station, Central Research & Development Department, Wilmington DE 19880-0328 USA ABSTRACT Scanning tunneling microscopy (STM) images of the cleaved surfaces of Bi2Sr 2CaCu 20 8 (2212), Bi2Sr 2CuO 6 (221), and the Pb-substituted Bi1.5Pbo.5Sr 2CuO6 (Pb-substituted 221) at room temperature have been obtained. On the 2212 (Tc=85 K) compound, high resolution images show striations -10 A to 30 A wide. Similar striations of a periodicity of -27 A are also observed on the 221 (Tcýl 0 K) compound. On the Pb-substituted 221 (Tc=25 K) compound, no periodic structure can be observed. On samples oriented with Laue reflection, the striations are observed to run parallel to the a or b axis of the crystal. These striations are likely to be associated with the undulations along the b axis of the Bi layer observed in recent transmission electron micrographs. For the 2212 compound, comparison of the dependence of scan line characteristics on tunneling bias with calculations on the density of states of each elemental component around the Fermi energy also suggests that tunneling occurs on the Bi face. The topographical and tunneling bias dependence results show that the Bi-rich surfaces of these new superconductors is essentially a termination of the bulk structure even though structural or chemical defects are common. Scanning tunneling microscopy [1] (STM) has been successfully applied to a large variety of materials for atomic resolution imaging of surface structures. With voltage dependent STM [2,3] and scanning tunneling spectroscopy [4], surface electronic structures have also been obtained. The new layered Bi-containing superconductors, unlike the earlier rare earth copper oxide superconductors, can be studied with the STM in ambient atmosphere. The distinctive cleavage plane implies that scanning most likely takes place on one specific face of the structure. Reasonably large crystals of these compounds can be readily synthesized. We report both topographical and voltage-dependent STM results and first-principles pseudofunction calculations on these new materials. The superconductors studied have the following nominal chemical compositions: Bi2Sr 2 CaCu 2 08 (2212) [5],
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