date:IBM CORP,DIV RES,ZURICH RES LAB,CH-8803 RUSCHLIKON,SWITZERLAND
Dy2O3 buffer layers and subsequently DyBa2CU3O7 films have been grown on SrTiO3 by molecular-beam epitaxy. Electron-diffraction patterns clearly show that the bilayer system grows epitaxially on SrTiO3. RHEED patterns suggest the formation of Dy2O3 domains, which is confirmed by transmission-electron microscopy. The domains have typical sizes between 10 and 40 nm and are separated by boundaries parallel to the substrate normal. On the basis of crystallographic analysis and image calculations we relate the formation of such domains to a twinning process. Evidence of twins is found both at domain boundaries as well as inside single domains. Scanning electron microscopy and transmission-electron microscopy show that the DyBa2Cu3O7 films are smooth, which indicates that twinned Dy2O3 surfaces do not preclude the growth of high-quality superconducting films.