Study of growth spirals and screw dislocations on YBa 2Cu 3O 7− δ single crystals

Abstract

Square, octagonal or polygonal growth spirals and growth hillocks were observed on the (001) surface of YBa 2Cu 3O 7− δ 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 ∼1 and 62 μm for macro-spiral and ∼8–10 nm and ∼8 μm 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.