Different morphologies of Au@Ag nanocrystals have been successfully synthesized using iodide ions in growth solutions consisting of ascorbic acid, NaOH, and CTAB. Without I- ions in growth solution, there were unnoticeable changes in morphology. On the other hand, with addition of I- ions, remarkable changes were observed including formation of hexagonal bipyramidal nanocrystals. Ag+ ions were reduced and deposited on {1 1 1} facets of gold hexagonal nanoplates (GHNs), and hexagonal bipyramidal nanoparticles were formed more quickly in the presence of I- ions than without I- ions. Our studies reveal that I- ion affects the selective growth of Ag onto GHNs. This can be explained by the decrease in the surface redox potential of nanocrystals that occurs by combining with the AgI complex on the metallic surface. These results were confirmed by FESEM images, UV-vis-NIR spectra, and TEM images. (C) 2012 Elsevier Inc. All rights reserved.