PhD: Nuria Bagués

Directors: Dr José Santiso López, Nanomaterials Growth Division Leader at ICN2 and Dr Felip Sandiumenge Ortíz, Advanced Characterization and Nanostructure group Magnetic Material and Functional Oxide Department at ICMAB

Short Abstract: Epitaxial thin films of functional perovskite-type oxides present interfacial coupling and misfit relaxation mechanisms governed by a complex interplay between chemical, electronic and structural degrees of freedom. The relaxation mechanisms of strained films may accommodate defects, such as misfit dislocations or twin walls, which exhibit a strong tendency towards self-organization with characteristic length scales of tens of nanometres. The core lattice structure of these defects is different from the bulk of the material and thus may be considered as a nano-phase with likely different physical properties, leading to the formation of functional nanostructures. The correlation between defect structure and functionality, together with the capacity of these defects to self-organize, offers a unique opportunity for the bottom-up elaboration of functional complex oxides nanodevices.

This thesis focuses on the characterization of the atomic and chemical structure of the interface and self-organized defects of epitaxial films and functional nanostructures of oxide materials by using advanced transmission electron microscopy. The materials studied in this work may be regarded as nanostructured films resulting from the self-organization of misfit relieving defects as follows: nanoinclusions of a MnOx phase (volume defects) in LaMnO3; twin walls between twin domains (planar defects) in La0.7Sr0.3MnO3 on SrTiO3; and misfit dislocations (line defects) in La0.7Sr0.3MnO3 on LaAlO3. The results and main conclusions obtained in this work open new perspectives for the development of functional self-organized nanostructures based on strain relieving defects.