Oxide Nanostructures

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Self-assembled nanoparticle systems and nanocrystalline photoelectrodes that are functionalized with organic molecules are key examples of hybrid nanomaterials with functional properties of technological impact. This project aims at the controlled fabrication of hybrid metal oxide/ organic molecule structures down to the nanometer scale. With this approach the funCOS 5 project addresses one major goal of the whole consortium, which is the functional landscaping of molecular films on oxide surfaces. The corresponding oxide nanostructures as complementary funCOS model systems will be fabricated by a variety of techniques reflecting the specific expertise of the funCOS 5 partners. The main methods are: adsorption of functional molecules, in particular porphyrins, on thin metal oxide films, an approach in which a focused electron beam is employed to locally dissociate an appropriate precursor or to nanolithographically activate oxide supports in UHV, chemical vapor synthesis of oxide nanoparticles and self-organized anodic nanostructure growth in electrolyte solution. We will establish robust synthesis and growth protocols for the generation of supported and unsupported oxide nanostructures of variable compositional complexity. These will range from transition metal oxide (CoO) doped host oxides (MgO) to composites and CoOx-TiO2 superlattice-like nanotubular structures. We will address structure formation and its impact on adsorpion and reactivity on different length scales. Thereby, the structures will be optimized to act as templates for the adsorption of porphyrin molecules to yield hybrid materials with specific properties.With and without supporting substrates, the adsorption behavior of the porphyrins and their organization at different length scales will reveal structure and materials specific factors that will enable to balance molecule-substrate and molecule-molecule interactions. Specific local interactions between characteristic oxide surface features (e.g. corners, edges, thermally and electron beam induced oxygen vacancies) and organic linkers and/ or porphyrins will be addressed. Resulting model structures will enable us to link insights from surface science studies on 2D surfaces (funCOS 1-3) to 3D hybrid nanostructures. Moreover, we will elucidate the impact of residual water molecules and hydroxyls i) on nanostructure stability, ii) on the adsorption of porphyrins and functional groups in general and iii) on the resulting functional performance. The close cooperation with funCOS 1-4 and 6 will enable us to transfer atomic scale insights obtained by surface science techniques on atomically clean, single crystalline surfaces to 2D nanostructured templates and 3D high-surface-area materials of variable structural and compositional complexity.