Bimetallic Bifrustums

Add two-tone triangular bifrustums to the list of unusual nanocrystal shapes and compositions that can be prepared synthetically. Researchers at Northwestern University report that they have synthesized these structures, which are truncated (flattened) triangular bipyramids as nanocrystals with gold cores and silver shells (Nano Lett., DOI: 10.1021/nl901513g). Bimetallic triangular crystals could serve as test subjects for studying relationships among crystal structure, composition, and electronic and optical properties. But the unusual crystals have been tough to synthesize. Northwestern's Hyojong Yoo, Chad A. Mirkin, George C. Schatz, and coworkers succeeded in making the tiny structures by using an aqueous route in which silver layers grow on gold nanoprism seed crystals. The crystals' surface plasmon resonances (SPRs)—a property that can lead to intense fluorescence and Raman spectroscopy signals—can be tuned easily throughout the UV-visible and near-IR regions by synthetically controlling the thickness of the silver shells. That property may make the crystals useful for applications in biodiagnostics and spectroscopy.