Nearly Untwinned Superconducting Bi₂Sr₂CuO_y Thin Films Grown on (Y, Nd)AlO₃ (001) Substrate

Abstract

Superconducting Bi 2 Sr 2 CuO y thin films were prepared in situ by molecular beam epitaxy with pure ozone gas. Films were deposited on SrTiO 3 (001) and (Y, Nd)AlO 3 (001) substrates, and their surface structures (Bi-O layer) were observed by reflection high-energy electron diffraction. While the film on the SrTiO 3 substrate had incommensurate modulated structures equivalently along both the SrTiO 3 [110] and SrTiO 3 [1̄10] directions, the modulated structures of major domains of the film on the (Y, Nd)AlO 3 substrate ran along the (Y, Nd)AlO 3 [100] direction. The origin of the in-plane orientation is related to the in-plane lattice constants of (Y, Nd)AlO 3 and Bi 2 Sr 2 CuO y .