Surface outgrowths on sputtered YBa₂Cu₃O_7−x films: A combined atomic force microscopy and transmission electron microscopy study

We have structurally and morphologically characterized the surface of sputtered YBa₂Cu₃O_7−x films on (001) SrTiO₃ using atomic force microscopy and transmission electron microscopy. Atomic force microscopy reveals three types of outgrowths with different shapes and heights between 2 and 200 nm: type I exhibits cubic habit, type II tabular habit, and type III is an agglomerate of no particular shape. Some of the type‐III outgrowths are located at the center of growth spirals where the screw dislocation intersects the film surface, suggesting that in YBa₂Cu₃O_7−x films these defects promote the occurrence of one another. Using high‐resolution electron microscopy and electron diffraction the surface outgrowths have been identified as follows: type I is Y₂O₃, type II Y₂O₃ and CuYO₂, and type III YBa₂Cu₃O_7−x, CuO, and Y₂O₃. In contrast to types‐I and ‐II outgrowths which are both epitaxially related to the surrounding YBa₂Cu₃O_7−x, the large type‐III agglomerates consist of epitaxial and nonepitaxial grains. As it is found that the outgrowing nonepitaxial phases emanate from screw dislocations and from a,b‐axis domain boundaries, it is suggested that both internal stresses and high interfacial energies promote such outgrowths on YBa₂Cu₃O_7−x films.