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High Resolution Image Download MS PowerPoint Slide The production of colloidal metal nanostructures with complex geometries usually involves shape-directing additives, such as metal ions or thiols, which stabilize high-index facets. These additives may however affect the nanoparticles’ surface chemistry, hindering applications, e. g. , in biology or catalysis. We report herein the preparation of gold bipyramids with no need for additives and shape yields up to 99%, using pentatwinned Au nanorods as seeds and cetyltrimethylammonium chloride as surfactant. For high-growth solution: seed ratios, the bipyramids exhibit an unusual “belted” structure. Three-dimensional electron microscopy revealed the presence of high-index 117, 115, and 113 side facets, with 113 and 112 facets at the belt. Belted bipyramids exhibit strong near-field enhancement and high extinction in the near-infrared, in agreement with electromagnetic simulations. These Ag-free bipyramids were used to seed chiral overgrowth using 1, 1′-binaphthyl-2, 2′-diamine as a chiral inducer, with g -factor up to 0. 02, likely the highest reported for bipyramid seeds so far.
Bevilacqua et al. (Thu,) studied this question.