| Abstract
| - The seed-mediated growth of gold nanostructures is shown to be strongly dependent on the gold seednanocrystal structure. The gold seed solutions can be prepared such that the seeds are either single crystallineor multiply twinned. With added silver(I) in the cetyltrimethylammonium bromide (CTAB) aqueous growthsolutions, the two types of seeds yield either nanorods or elongated bipyramidal nanoparticles, in good yields.The gold nanorods are single crystalline, with a structure similar to those synthesized electrochemically (Yu,Y. Y. et al. J. Phys. Chem. B1997, 101, 6661). In contrast, the gold bipyramids are pentatwinned. Thesebipyramids are strikingly monodisperse in shape. This leads to the sharpest ensemble longitudinal plasmonresonance reported so far for metal colloid solutions, with an inhomogeneous width as narrow as 0.13 eV fora resonance at ∼1.5 eV. Ag(I) plays an essential role in the growth mechanism. Ag(I) slows down the growthof the gold nanostructures. Ag(I) also leads to high-energy side facets that are {110} for the single crystallinegold nanorods and unusually highly stepped {11n} (n ∼ 7) for the bipyramid. To rationalize these observations,it is proposed that it is the underpotential deposition of Ag(I) that leads to the dominance of the facets withthe more open surface structures. This forms the basis for the one-dimensional growth mechanism of singlecrystal nanorods, while it affects the shape of the nanostructures growing along a single twinning axis.
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