Scanning tunneling microscopy studies of NdBa2Cu3O7-delta single crystals

We have performed scanning tunneling microscope/spectroscopy measurements o n NdBa2Cu3O7-delta (Nd123) single crystals. Two characteristic structures, i.e., square lattice and one-dimensional atomic structures are observed on the naturally terminated layers. For a cleaved surface, nm size bright and dark regions consisting of a 4 x 4 Angstrom (2) square lattice are observed and the contrast is explained by the inhomogeneous distribution of oxygen vacancies on the surfaces. (C) 2001 Elsevier Science B.V. All rights reserv ed.