Right bipyramids of silver: A new shape derived from single twinned seeds

Silver nanoparticles with a single (1111) twin were selectively nucleated and grown for the first time to produce right bipyramids 75-150 nm in edge length. Key to the production of single twinned seeds was the addition of NaBr to a polyol synthesis in which AgNO(3) is reduced by ethylene glycol in the presence of poly(vinyl pyrrolidone). Examination of nanoparticles; at different stages of the reaction with electron microscopy revealed that the spherical, single twinned seeds grew to become right bipyramids through enlargement of their (100) facets. The UV-vis-NIR spectrum exhibited by right bipyramids is distinct from that of any other silver nanostructure, and their sharp corners make these new nanoparticles especially promising for enhancement of Raman scattering.