Nucleation of a Complex Oxide during Epitaxial Film Growth: ${{\mathrm{SmBa}}_2{\mathrm{Cu}}_{3}O}_{\mathit{y}}$ on SrTi${\mathrm{O}}_3$

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 SmB${\mathrm{a}}_2$C${\mathrm{u}}_3$ ${\mathrm{O}}_7$ deposited by reactive molecular beam epitaxy on a (100) SrTi${\mathrm{O}}_3$ 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.