Studies of Hexagonal Pt and Au Nanocluster Superlattices

Abstract We have recently synthesized superlattices of Pt and Au nanoclusters grown by inverse micelle techniques. The monodisperse nanosize metal clusters used in this study were synthesized as surfactant aggregates surrounded by an oil-like environment (inverse micelle), a technique developed and patented at Sandia. Reaction byproducts, such as excess surfactant and inorganic ion salts, are often separated from the metal clusters using liquid chromatography size exclusion techniques; however, the Pt and Au nanoclusters in this study have been fractionated using a liquid-liquid technique. The nanoclusters are capped with a ligand. Two-dimensional hexagonal arrays formed readily on surfaces, and large twinned three-dimensional crystals form from solution. Both the cluster size and the size of the capping ligand can be controlled to form superlattices having a range of lattice parameters. We have found that the capping agent exerts a marked influence on the tendency of these clusters to order.