Effect of ligand-metal interactions on the growth of transition-metal and alloy nanoparticles

The growth of cobalt, iron, and platinum and their alloy nanoparticles was investigated with oleic acid and trioctylphosphine oxide as ligands. Both the ligand type and concentration are important in determining the final product of the reactions. With a high concentration of oleic acid, thermal decomposition of dicobalt octacarbonyl and iron pentacarbonyl precursors yields only molecular cluster complex species with oxidized metal centers. However, reduction of platinum acetylacetonate under identical conditions yields nanometer-sized particles. In the presence of a high concentration of trioctylphosphine oxide, only the cobalt system was observed to form a cluster-complex species, while both the iron and platinum systems form nanometer-sized particles. This oxidation process, which forms cluster complexes, provides a digestive ripening mechanism that competes with the Ostwald ripening process, thus affecting the particle size and composition of both the pure metal and alloy nanoparticles.