In-Plane Orientations and Grain Boundaries of YBa2Cu3O7-x Thin Films on (001)MgO Substrates Grown by Metalorganic Chemical Vapor Deposition

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Abstract
Growth orientations and structures of YBa2Cu3O7-x (YBCO) thin films on (001) MgO substrates formed by metalorganic chemical vapor deposition (MOCVD) were investigated by means of X-ray diffraction, and plan-view and cross-sectional transmission electron microscopy (TEM). Less than half of the films are epitaxially grown (001)-oriented films, and the rest are films composed of epitaxial grains and in-plane misoriented grains with specific misorientation angles. Cross-sectional TEM revealed that the in-plane misoriented grains are grown on a flat MgO surface, while the epitaxially oriented grains are grown on MgO with surface atomic steps as large as 1 nm. The misoriented films are composed of large grains several µm in size with large-angle grain boundaries (LAGBs), and each grain contains several small grains less than 1 µm in size with slight mutual misorientations. A clear Josephson effect was observed from the films with the LAGBs. From the lattice imaging, it was found that the LAGBs tend to form lower Σ structures. A TEM microbeam analysis revealed an oxygen deficiency at the LAGBs.