Growth of Ge nanowires from Au-Cu alloy nanoparticle catalysts synthesized from aqueous solution

Elemental metal nanoparticles are widely used to catalyze semiconductor nanowire growth, but size-controlled alloy nanoparticles have not been explored in this context. We present a simple aqueous synthesis of Au-Cu₂O core-shell nanoparticles to produce Au-Cu alloy nanoparticles of controlled size and composition by vacuum annealing. Colloidal Au nanoparticles were used as size-controlled seeds, and fine control of the Cu₂O shell thickness enabled tuning of the average Au-Cu alloy composition. The alloy nanoparticles were found to catalyze Ge nanowire growth in a low-pressure chemical vapor deposition environment. The nanowire growth rate for Au-Cu nanoparticles was intermediate to that of Cu (slowest) and Au (fastest) nanoparticles under identical conditions, suggesting a vapor-solid-solid growth process. These catalysts provide a useful platform to explore the influence of catalyst phase and chemistry on nanowire growth mechanisms that determine important variables including the doping rate and junction abruptness.