MICROSTRUCTURES AND PRECIPITATES IN LASER-ABLATED YBCO THIN-FILMS ON SRTIO3 (110)

Thin YBCO films (approximately 100 nm) have been deposited by laser ablation on SrTiO3 (110) substrates. Microstructural investigations have been performed by scanning tunneling and high-resolution electron microscopy. The results show that the surface corrugation is related to the growth of twisted YBCO domains that nucleate at the film/substrate interface. The twist is characterized by a 90-degrees rotation of YBCO around the [100] and/or [010] axes, which results in {013} and/or {103} planes parallel to the substrate surface. Precipitates belonging to Y2O3 are densely distributed on the film surface. No such second phases have been identified inside the YBCO films. The orientational relationship between precipitates and film is such that the lattice mismatch is minimized in the interface planes. A large number of precipitates grow from the film surface outwards. This phenomenon can be explained on the basis of lattice matching arguments and favorable growth kinetics.