Nucleation of a Complex Oxide during Epitaxial Film Growth: SmBa2Cu3Oy on SrTiO3

Film growth of a complex oxide is investigated during nucleation on a substrate surface. Using atomic force microscopy we have imaged subunit cell coverage of SmBa₂Cu₃O₇ deposited by reactive molecular beam epitaxy on a (100) SrTiO₃ substrate. After a threshold deposition, c-axis islands are observed to nucleate predominantly along the surface steps. The heights of the nucleation islands are examined and a consistent layer stacking model is proposed. Cation stoichiometry of the nucleation islands is inferred to be dependent on the substrate surface and different from the bulk.