Nanoparticle Synthesis and Characterization
Nanoparticles offer a larger surface to volume ratio, a higher concentration of undercoordinated surface sites and, due to strong interplay between elastic, geometric and electronic parameters, as well as effects of interaction with support, often improved or unique physical and chemical properties compared to the corresponding bulk material. The Au/TiO2 system is a prime example of how gaining control over the nanoparticle size can improve the specificity and yield of a catalytic reaction.
We produce nanoparticles of a range of metals (e.g. Ag, FePt), semiconductors (e.g. CdSe, CdTe), and metal oxides (e.g. MnO,3 CuxO4, FexOy5, TiO2, ZnO,1 BaTiO36) with highly uniform size distributions. For several material systems, we developed methods that offer tight control over the nanoparticle morphology, crystal structure and stoichiometry. Our selection of the target material is motivated by an application and the hypothesis of enhanced properties.
For example, several oxide nanoparticles (i.e. copper oxide shown on the right) offer catalytic abilities, which depend on nanoparticle size and differ from the bulk material. In most cases, semiconductor and transition metal oxides are produced by introduction of chemically reactive molecular precursors into inert solvents, in which they combine - in the presence of ligands - to form the desired nanocrystalline product through pyrolysis, decomposition or other chemical reaction. For metals, the synthesis relies on phase transfer reduction of metal salts in the presence of a stabilizing ligand.
For general characterization of the nanoparticles, a large number of techniques are necessary including NMR,8 electron microscopy (SEM, TEM), X-ray diffraction, scanning probe microscopy. With the possibilities in nanoparticle synthesis increasing tremendously with regards to size control, reproducibility and structural complexity, it becomes more and more urgent to define particular directions for the field to follow. Our immediate objective is to establish the ground rules that will take us to rational approaches for chemical synthesis of nanomaterials
(a) a monolayer on the TEM grid surface (b) a superlattice, in which the nanoparticles have self-assembled into a close packed structure (c) HRTEM lattice imaging showing single crystal and lattice spacings (d) selected area electron diffraction pattern.