Evidence for the Growth Mechanisms of Silver Nanocubes and Nanowires

Ethylene glycol reduction of silver nitrate at 140 degrees C in the presence of poly(vinyl pyrrolidone) (PVP) and HCl is a facile method to prepare uniform silver nanocubes et al., Angew. Chem., Int. Ed. 2005, 44, 2154). We reported herein that the product switches from uniform silver nanocubes to uniform silver nanowires by simply aging the freshly prepared AgNO3 solution under ambient atmosphere for 5 mm without the change of any other react:ion parameters. The aging process was found to increase the density of silver seeds and, more importantly, to change the population of single and twinned crystal seeds. The portion of twinned-crystal seeds is less than 30% of total silver seeds in the freshly prepared AgNO3 solution but more than 60% of total silver seeds in the AgNO3 solution aged for 5 min. We proposed that twinned-crystal silver seeds in the freshly prepared AgNO3 solution can be adequately etched in the subsequent etching and growth process, leading to the growth of silver nanocubes, but that those in the AgNO3 solution aged for 5 min can not, leading to the growth of silver nanowires. Twinned-crystal silver seeds in the AgNO3 solution aged for 5 mm could be effectively etched by the increase of the concentration of HCl, yielding uniform silver nanocubes again. These results unambiguously prove the important role of twinned-crystal seeds in the growth of anisotropic silver metal nanowires and also indicate that the morphology of silver nanostructures prepared by the polyol process in the presence of PVP can be tuned by controlling the interplay between the population of twinned-crystal silver seeds and the concentration of HCl, greatly deepening the fundament:al understanding of the growth mechanisms of silver nanocubes and nanowires.