Synthesis and Characterization of Au/Bi Core/Shell Nanocrystals:  A Precursor toward II−VI Nanowires

The synthesis, characterization, and catalytic ability of gold/bismuth (Au/Bi) core/shell nanocrystals for promoting asymmetric 1D nanowire growth is described. A biphasic gold reduction approach is initially used to create small (1.5 nm diameter) Au particles passivated with trioctylphosphine (TOP). The alkylphosphine ligands render the Au nanocrystals soluble in common organic solvents used for II−VI semiconductor nanocrystal/nanorod growth. Subsequent surface passivation with elemental bismuth is accomplished through the thermolysis of trialkylbismuthines at 100 °C in a mildly coordinating solvent. The resulting core/shell particles are characterized by using a variety of techniques including transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDXS) to demonstrate successful overcoating of the Au nanoparticles. Resulting diameters range from 1.43 to 2.53 nm, with the as-made Au/Bi nanocrystals stable for weeks to months when stored at low temperature under an inert atmosphere. Catalytic activity, promoting the asymmetric growth of II−VI semiconductor nanowires, is demonstrated for the particular case of CdSe, illustrating a relatively simple route for making high-quality, narrow-diameter (<10 nm) 1D materials capable of exhibiting quantum confinement.