The Origin of the Superstructure in Bi2Sr2CaCu2O8+δ as Revealed by Scanning Tunneling Microscopy

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Science  23 Dec 1988:
Vol. 242, Issue 4886, pp. 1673-1675
DOI: 10.1126/science.242.4886.1673


Real-space images with atomic resolution of the BiO plane of Bi2Sr2CaCu2O8+δ were obtained with a scanning tunneling microscope. Single-crystal samples were cleaved and imaged under ultrahigh vacuum conditions at room temperature. The images clearly show the one-dimensional incommensurate superstructure along the b-axis that is common to this phase. High-resolution images show the position of the Bi atoms, revealing the structural nature of the superlattice. A missing row of Bi atoms occurs either every nine or ten atomic sites in both (110) directions, accounting for the measured incommensurate periodicity of the superstructure. A model is proposed that includes missing rows of atoms, as well as displacements of the atomic positions along both the a- and c-axis directions.