Study of growth spirals and screw dislocations on YBa2Cu3O7-δ single crystals

Square, octagonal or polygonal growth spirals and growth hillocks were observed on the (001) surface of YBa2Cu3O7-delta single crystals grown from a Ba/CuO flux. Study of the spiral morphology is indicative of the long [100]/[010] steps parallel to Cu-2-O-3 chains and the short [110] ones parallel to Ba-O-2 chains. The height and the width of spiral steps were estimated to be similar to 1 and 62 mu m for macro-spiral and similar to 8-10 nm and similar to 8 mu m for micro-spiral by atomic force microscopy. There is clear evidence for a screw dislocation etch pit corresponding to growth spiral on the (001) surface, after being exposed by chemical etching. The morphology of the screw dislocation etch pits exhibits a tetragonal structure feature bounded by (100)/(010) and truncated by (110) edges, and composed of singular faces {100}, {110} and {111}. All the etched samples displayed polar character with pyramidal etch pits and flattened pits in the {001} surface. (C) 2000 Elsevier Science B.V. All rights reserved.