Synthesis and Optical Properties of Flower- and Spiky-Ball-Like Silver-Gold Nanoparticles

Flower- and spiky-ball-like nanoparticles were selectively obtained by the reduction of H[AuCl4] and AgNO3 with ascorbic acid in the presence and absence of poly(vinylpyrrolidone) with sufficient reproducibility. The morphological switch is attributable to the selective passivation of the crystal facets of the initially grown core particles and growing nanostructures on the surfaces. The characteristic optical properties, which are due to the surface nanostructures, were studied via measurement of the extinction spectra and finite-difference time-domain simulations.