GROWTH DEFECTS AND INTERFACE ROUGHNESS IN YBA2CU3O7 SRTIO3 SUPERLATTICES GROWN BY PULSED-LASER ABLATION/

YBa2Cu3O7/SrTiO3 heterostructures interface roughness and defect forma tion have been studied by TEM and HREM. We have used a tripod ionless thinning method which avoids the diffusion defects induced by ion mill ing bombardment to identify intrinsic defects issued from the process. The results show that interface roughness varies across the superlatt ices. Extended defects like twinning, which are induced by the heteroe pitaxy of the SrTiO3/YBa2Cu3O7 interface, propagate across a few layer s. Furthermore, typical conical defects have also been observed, which are due to plastic deformation. They also propagate across the epitax ial structure from the first inverse interface to the surface, produci ng dislocations, grain boundaries and roughness increase. These defect s which are not developed when the SrTiO3 epi-layer is grown on an a-a xis YBa2Cu3O7 destroy the structural coherence at the scale of X-rays, although the chemical periodicity which is evidenced from SIMS profil e analyses is not affected.