HIGH-RESOLUTION ELECTRON-MICROSCOPY OF EPITAXIAL YBCO/Y2O3/YSZ ON SI(001)

The microstructures of YBa2Cu3O7-delta (YBCO) thin films grown on Si with Y-stabilized ZrO2 (YSZ) and Y2O3 buffer layers were characterized by means of high-resolution electron microscopy. At the Si-YSZ interface, a 2.5 nm thick layer of regrown amorphous SiO(x) is present. The layer is interrupted by crystalline regions, typically 5 to 10 nm wide and 10 to 50 nm apart. Close to the crystalline regions, {111} defects are present in the Si substrate. The typical defect observed is an extrinsic stacking fault plus a perfect dislocation close to the stacking fault which terminates extra {111} planes in the upper part of the Si. These defects are probably formed by condensation of Si self-interstitials created during oxide regrowths Precipitates are present in the Si close to the Si-YSZ interface and indicate that in-diffusion of Zr has occurred. The YSZ-Y2O3 interface is atomically sharp and essentially planar and contains no second phases. Perfect misfit dislocations with Burgers vector 1/2[110] are present at this interface along with unrelaxed elastic misfit stresses. The Y2O3-YBCO interface is atomically sharp and planar, but contains steps. (001) stacking faults are present in the YBCO above these steps; the faults are, however, healed a few unit cells away from the interface. By HREM analysis of ultrathin specimen areas, the atomic layer of the YBCO closest to the Y2O3 was found to be a barium-oxygen layer.