Nanoscopic building blocks from polymers, metals, and semiconductors

Aiming at the fabrication of nano-structured materials and hybrid aggregates we synthesize and characterize nanoscopic objects from polymers, noble metals, and semiconducting materials. As an example for the preparation of mesoscopic functional assemblies we first describe the layer-by-layer deposition of dendritic building blocks to the walls of nanometric pores in an anodized alumina (Al₂O₃) substrate used as template. After dissolution of the matrix hollow nano-tubes are obtained with an outer diameter that corresponds to the pore diameter and with a wall thickness that is determined by the number of layers deposited. The tube length is given by the pore depth of the template and reaches in our examples up to 80 micrometers. Next, a single colloid particle-based templating protocol for the fabrication of non-trivial Au nanostructures is described. The obtained nano-crescents can be varied in terms of their size and shape over a wide range (at the hundreds of nanometers scale). Their plasmonic resonance behavior, e.g., the spectral position of their (multipole) absorbance peaks shows a characteristic dependence on the polarization of the exciting laser light. Finally, the optical properties of colloidal semiconductor (quantum dots) are analyzed. In particular, the spectral photoluminescence properties are described for nanotube assemblies that are fabricated by the deposition of (positively charged) dendrimers alternating with (negatively charged) quantum dots of different emission wavelength (energy transfer cascades). The last example of a hybrid assembly concerns the electronic coupling of (the HOMO/LUMO levels of) semiconducting nanoparticles to (the Fermi level of) a gold electrode.