Microscopic observation of interface structures of YBaCuO/MgO/YBaCuO double-heteroepitaxial thin films by TEM

The YBaCuO/MgO/YBaCuO double-heterostructure (DHS) was fabricated using conventional RF magnetron sputtering. The formation of [110]YBaCuO/[100]MgO/[110]YBaCuO on [110]SrTiO/sub 3/ substrate, and [001]YBaCuO/[100]MgO/[100]YBaCuO and [001]YBaCuO/[100]MgO/[001]YBaCuO on [100]MgO substrate are demonstrated. According to RHEED (refraction high-energy electron diffraction) observations, each layer of the DHS was grown epitaxially. The cross-sectional TEM (transmission electron microscope) observation of the [001]YBaCuO/[100]MgO(2 nm)/[001]YBaCuO structure was carried out in order to characterize the heterostructure. The ultrathin MgO layer grew in an island shape. The MgO shape deposited on YBaCuO film is island-like because of the low absorption energy of Mg on the YBaCuO surface and/or large value of MgO/YBaCuO interface free energy. The YBaCuO atomic arrangement shape implied that the YBaCuO growth mechanism was atomic layer epitaxy.