Enhanced film quality of Y-Ba-Cu-O by using Eu-Cu-O buffer layer on Sr-Ti-O substrates

Eu₂CuO₄ (ECO) has been used as a buffer layer for growing of YBa₂Cu₃O_7-δ (YBCO) thin films on SrTiO₃ (STO) (100) substrates. The epitaxy, crystallinity and surface of YBCO thin films have been significantly improved by using ECO buffer layer as investigated by x-ray diffraction, rocking curves, scanning electron microscope, surface step profiler and x-ray small angle reflection. The best value of the full width at half maximum of the YBCO (005) peak can be greatly reduced down to less than 0.1 degree. The scanning electron microscope photos indicate very smooth surface for the YBCO thin films. The average roughness is less than 5 nm over a wide scanning region of 2000 μm. The results of x-ray small angle reflection indicate a very clear and flat interface between YBCO and ECO layers. Our results suggest that ECO should be a good barrier candidate for fabricating high-T_c superconductor junctions