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

Abstract

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.