Tesis doctoral de Marta Gibert Gutiérrez
In this work we have investigated a bottom-up high-throughput methodology to generate interfacial self-assembled oxide nanostructures through the deposition of chemical solutions. The innovation of this work is two-fold, since we have studied the application of self-assembling and self-organizing processes to oxide materials and because the study of the formation of interfacial islands from solutions. These templates have been used to optimize the vortex pinning capabilities of yba2cu3o7 (ybco) thin films. systematic studies based on the modification of growth conditions show the capabilities and versatility of the methodology used to tune the shape, size, density and distribution of the resulting oxide interfacial nanoislands. Specifically, we have studied the growth of nanostructures of the oxides phases bazro3, ceo2, ce0.9gd0.1o2-y (cgo) y la2o3, leading to the generation of templates with interfacial nanoislands with narrow distribution of sizes and notable tendency to form ordered arrays on top of the single-crystal substrates srtio3 y laalo3 (lao). We have determined a range of parameters which establish a set of initial conditions for the generation of interfacial nanoislands of other oxide phases. the system of dissimilar structures cgo/lao (fluorite/perovskite) is analyzed in great detail as a model to study the formation and growth of strain-induced nanoislands. The capacity to select the crystallographic orientation of cgo nanoislands through tuning of growth conditions enables us to control the anisotropy of strains and surface energies of the nanoislands, leading to the formation of cgo nanostructures with different morphological and kinetic characteristics. Square-based isomorphic nanoislands, uniform and stable, form under isotropic strains. These nanodots grow epitaxially (001)cgo[110]||(001)lao[100]; they have mean lateral size ~45 nm and ~7 nm height, and density of ~60 dots/¿m2 anf order into rows along lattice steps of the substrate, resulting into highly self-organized templates. Instead, highly elongated rectangular nanostructures (nanowires) grow induced by anisotropic strains in the epitaxial relation (011)cgo[100]||(001)lao[100]. Wires long axis reaches lengths of 2 ¿m in less than 30 minutes of heat treatment whereas short axes remain <50 nm, resulting in high lateral aspect ratios (long axis/short axis ~ 40). Wires are aligned along substrate soft axes and continuously join into intricate clusters of orthogonal wires which rapidly reconstruct into larger wires. The attractive interaction between wires is the driving force of the ultrafast kinetics of these islands. The ultrarapid dynamics has allowed the study of the evolution of interfacial nanoislands identifying several coarsening mechanisms. simulations based on thermodynamic models have enabled to confirm the equilibrium shape and size of each sort of cgo island in relation to its misfit strain and surface energies. The combined analyses of the experimental results and thermodynamic studies have permitted to establish a list of the requirements for the formation of extremely long interfacial nanowires. These strategies are not limited to oxides and can be extended to the generation of anisotropic nanoislands in a large variety of systems, proving the generality of the work done. finally, we have showed a practical application of oxide nanostructured templates to induce artificial vortex pinning centres in ybco thin films also prepared from solutions. A strong improvement of the anisotropic-strong contribution to the critical current density for h||c in interfacial nanostructured ybco thin films as compared to standard ones proves that interfacial nanostructuration is a possible and promising strategy to improve the performance of ybco thin films. Analyses of the superconducting properties as function of ybco thickness have also been carried out.
Datos académicos de la tesis doctoral «Self-assembled strain-induced oxide nanoostructures grown by chemical solutions«
- Título de la tesis: Self-assembled strain-induced oxide nanoostructures grown by chemical solutions
- Autor: Marta Gibert Gutiérrez
- Universidad: Autónoma de barcelona
- Fecha de lectura de la tesis: 09/02/2009
Dirección y tribunal
- Director de la tesis
- Xavier Obradors Berenguer
- Tribunal
- Presidente del tribunal: oliver g. Schmidt
- dave h.a. Blank (vocal)
- (vocal)
- (vocal)