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Layered oxide compounds are extensively studied for their application potentials as superconductors and ionic conductors. These layered structures can be considered as stacking sequences of perovskite layers, either with or without intervening rock-salt layers separating them, where planar defects such as stacking faults are often present. These structurally anisotropic defects, particularly near substrate interfaces in epitaxial thin film, can have dramatic effects on physical properties such as low-dimensional transport, diffusion and growth [1]. In this study we focus on the interfacial microstructure and defects in YBa2Cu3O7-x (YBCO) thin films grown on (LaAlO3) 0.3 (Sr2AlTaO6) 0.7 (LSAT) substrates. These films are ultimately intended for use in transport studies of multilayers comprising YBCO and La1-xCaxMnO3 (LCMO). High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) was used in our study. The STEM imaging was carried out with an FEI Titan3 80-300 TEM, equipped with a CEOS-designed hexapole-based aberration corrector for the probe-forming lens and imaging lens. The instrument is fitted with a high-brightness electron source and a Super-Twin lens, in order to achieve sub-Ångstrom resolution for phase contrast imaging, STEM, and electron energy loss spectroscopy (EELS) mapping, along with a monochromator in order to achieve energy resolutions as low as 0.1 eV [2]. Measurements were carried out at either 80 or 200 keV in order to reduce knock-on damage.

From HAADF intensities, we can unambiguously identify the sequence of layers and the intergrowths of Cu-O layers and extra Cu …