From single molecules to nanoscopically structured functional materials

The synthesis of MS₂ (M = Mo, W) onion-like nanoparticles by means of a high temperature MOCVD process starting from W(CO)₆ and elemental sulfur is reported. The reaction can also be carried out in two steps where the intermediate amorphous WS₂ nanoparticles formed through the high temperature reaction of tungsten and sulfur in the initial phase of the reaction are isolated and converted in a separate annealing step to onion-type WS₂ nanoparticles. Based on a study of the temperature dependence of the reaction a set of conditions could be derived where onion-like structures were formed in a one-step reaction. Onion-like structures obtained in the single-step process were filled, whereas the particles obtained by the two-step procedure were systematically hollow. A model could be devised to rationalize the different outcome of the reactions. The MOCVD approach therefore allows a selective synthesis of open and filled fullerene-like chalcogenide nanoparticles. Furthermore, we demonstrate the novel surface functionalization of WS₂ nanotubes with polymeric ligands by complexation with a combination of Ni²⁺ via an scorpionate-type nitrilotriacetic acid (NTA) and immobilization of TiO₂ nanoparticles onto the surface of nanotubes. Synthesis of such a functional polymeric ligand was achieved via a reactive polymer precursor route.