Atomic force microscopy study of bicrystal SrTiO3 substrates and YBCO thin films

Abstract

Single‐crystal substrates allow the epitaxial deposition of high‐Tc superconductor (HTS) films that exhibit high critical current densities (Jc). The decrease in Jc observed for films deposited on polycrystalline crystals is attributed to misorientation between adjacent grains. To understand better this phenomenon, deposition of HTS films on bicrystal substrates is used to model the effects of a single grain boundary. The surfaces of strontium titanate (001) bicrystals with tilt boundary orientations of 7°, 15° and 24° were analyzed by atomic force microscopy (AFM). Annealing conditions were found to be a key factor for obtaining atomically smooth surfaces. The grain boundary morphologies were analyzed from sections of the AFM images. Images of YBa2Cu3O7−x (YBCO) films produced on these substrates by pulsed‐laser deposition are shown for regions that include the grain boundaries. Different morphologies of YBCO thin films are presented. Copyright © 2000 John Wiley & Sons, Ltd.