Angew. Chem. Int. Edn 48, 4824–4827 (2009)

Credit: WILEY-VCH

Tiny silver crystals, which among other things are useful as catalysts and in biomedical imaging, like to form as cubes. But to allow better control of their properties, these crystals need to be coaxed into different shapes.

Younan Xia at Washington University in St Louis and his colleagues made silver nanocubes with a conventional reaction using silver nitrate solution, but then quickly added a small, additional amount of this solution. Three of the cubes' faces were augmented with extra silver atoms, creating a crystal that is half octahedron and half truncated cube (pictured). With slower addition of silver nitrate, the growing cubes remained cubic.

The authors suggest that the exotic crystal shapes could prove useful for an imaging technique called surface-enhanced Raman spectroscopy. Sharp tips, such as the points of an octahedron, help to focus the electric field.