Growth of untwinned Bi₂Sr₂Ca₂Cu₃O_x thin films by atomically layered epitaxy

We report the growth of untwinned epitaxial thin films of Bi‐Sr‐Ca‐Cu‐O by atomically layered heteroepitaxy on SrTiO₃ substrates. These films are c‐axis oriented as‐layered and do not exhibit 90° in‐plane defects, i.e., a‐b ‘‘twinning.’’ By misorienting the surface normal from {100} by approximately 4° towards 〈111〉, the cubic symmetry of the {100} surface is adequately broken to completely align the b axis of the superconducting film with respect to the substrate. Reflection high‐energy electron diffraction patterns observed during growth and post‐growth x‐ray diffraction analysis indicate that the incommensurate structural modulation occurs along the same direction as the step edges.