Epitaxial growth of YBCO/MgO/YBCO structures

A Y₁Ba₂Cu₃O_7-y(YBCO)/MgO/Y ₁Ba₂Cu₃O_7-y structure on a MgO(100) substrate was prepared, and its crystallographic structure was investigated by cross-sectional transmission electron microscopy (TEM). A MgO ultrathin film with (100) orientation as an intermediate layer was obtained on each of the (001) and (100) YBCO thin films at a substrate temperature of about 400°C. The crystallinity of the MgO layer was investigated as a function of the MgO thickness. The randomness of the crystallinity decreased with a decrease in the thickness. A (100) epitaxial MgO layer without other orientation was obtained at a thickness of 10 nm. From the results of cross-sectional TEM observation, it was found that the thickness of the MgO can be reduced to 5 nm at a minimum. In the sample with a MgO thickness of 5 nm, sharp interfaces were observed without any disrupted portion. When the thickness was reduced to 2 nm, the interface between the top layer and the base layer was crushed