Multiple heteroepitaxy and superlattice formation of LnBaCuO/YBaCuO system

Multiple heteroepitaxy and superlattice formation of high-T _c superconducting films were demonstrated. LnBaCuO/YBaCuO structures (Ln=Er, Nd) were realized as a preliminary stage. Superlattice formation made it clear that the crystal structure of the system strongly depends on the substrate materials. A (100)-oriented single-crystal MgO substrate provided a superlattice with the sound perovskite structure, whereas on (110) SrTiO₃ wafers a deformed crystal was formed. The study of ultrathin YBaCuO film epitaxy revealed that some kind of crystal, deformed from the perovskite structure but not identified yet, was found to grow on SrTiO₃ wafers regardless of their orientation at the beginning of the deposition, whereas the ultrathin perovskite crystal epitaxially grew on (100) MgO substrate. In addition, MgO thin film epitaxy on NdBaCuO was examined. RHEED patterns revealed that MgO epitaxially grew on both (110) oriented YBaCuO and SrTiO₃ with the orientation of (100) and (110), respectively