Surface outgrowths on sputtered YBa2Cu3O7−x films: A combined atomic force microscopy and transmission electron microscopy study

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Abstract
We have structurally and morphologically characterized the surface of sputtered YBa2Cu3O7−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 YBa2Cu3O7−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 YBa2Cu3O7−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.