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 YBa2Cu3O7-x films on (001) SrTiO 3 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 YBa 2Cu3O7-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 YBa2Cu3O7-x, CuO, and Y2O3. In contrast to types-I and -II outgrowths which are both epitaxially related to the surrounding YBa2Cu 3O7-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 YBa2Cu3O7-x films.