SURFACE OUTGROWTHS ON SPUTTERED YBA2CU3O7-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) SrTiO3 using atomic force microsc opy and transmission electron microscopy. Atomic force microscopy reve als three types of outgrowths with different shapes and heights betwee n 2 and 200 nm: type I exhibits cubic habit, type II tabular habit, an d 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 s crew dislocation intersects the film surface, suggesting that in YBa2C u3O7-x films these defects promote the occurrence of one another. Usin g high-resolution electron microscopy and electron diffraction the sur face outgrowths have been identified as folloWS: type I is Y2O3, type II Y2O3 and CuYO2, and type III YBa2CU3O7-x, CuO, and Y2O3. In contras t to types-I and -II outgrowths which are both epitaxially related to the surrounding YBa2Cu3O7-x, the large type-III agglomerates consist o f epitaxial and nonepitaxial grains. As it is found that the outgrowin g nonepitaxial phases emanate from screw dislocations and from a,b-axi s domain boundaries, it is suggested that both internal stresses and h igh interfacial energies promote such outgrowths on YBa2Cu3O7-x, filMS .