STRUCTURE OF THE GROWTH INTERFACE OF Y-BA-CU-O ANALOGS ON SRTIO3 (001) SUBSTRATES

The interface structures of c-axis-oriented ultrathin Gd-Ba-Cu-0 and E u-Ba.Cu-O films on SrTiO3 (001) substrates have been determined using x-ray standing waves. Rare-earth fluorescence profiles observed near t he 001 Bragg condition of SrTiO3 show a dip without a marked peak, whi ch can only be explained by either a BaO layer interfacing the TiO2 pl ane of SrTiO3 or the CuO or CuO2 layer interfacing the SrO plane. Calc ulations of x-ray field intensities using a simple rigid-sphere-ion mo del show that for both Gd-Ba-Cu-O and Eu-Ba-Cu-O neither the CuO layer nor the CuO2 layer can be the first grown layer on the TiO2 surface o f SrTiO3. Similarly, neither the BaO layer nor the rare-earth layer ca n be the first layer on the SrO surface.