Thin Film Structure of YBa2Cu3O7-δ on (001) MgO Substrate Studied by TEM

Abstract
A plan-view TEM observation was made for YBa2Cu3O7-δ (YBCO) thin films prepared by MOCVD on (001) MgO substrates. For the TEM observation, the MgO substrate plates were ion-thinned before the YBCO deposition. The YBCO thin films were found to be polycrystalline with a grain size of about 0.5 µm. Most of the YBCO grains are grown with their [001] axes nearly normal to the MgO substrate plane. Between the neighboring YBCO grains, a small-angle misorientation was observed quite frequently. Most of the misorientation angles measured by selected-area electron diffraction were less than about 5 degrees. At the small-angle grain boundaries, a nearly periodic array of dislocations was observed in the high-resolution lattice images. The AC and DC Josephson effects of YBCO thin film bridges reported previously are discussed in relation to the small-angle grain boundaries.