ACS Nano http://doi.org/sb2 (2014)

Crystals produced by biological processes often exhibit complex shapes and structures, which can have curved rather than faceted surfaces. By mimicking these processes, researchers have created a range of shaped single crystals from the ceramic materials (calcium carbonate, for example) that are also used by nature. However, achieving similar shapes with functional materials like metals has remained a challenge. Boaz Pokroy and colleagues at the Technion Israel Institute of Technology, the European Synchrotron Radiation Facility in Grenoble and Ghent University have now shown that gold single crystals can be grown with curved surfaces.

The researchers first created eutectic thin films of gold–germanium by evaporating layers of gold and germanium onto oxidized silicon wafers. The samples were subsequently annealed and, through a dewetting process, droplets of gold–germanium formed. The growth process then occurs confined within these droplets, which leads to gold crystals that replicate the shape of the droplets. To prove that the curved gold crystals were in fact single crystals, thin cross-sections of the droplets were prepared using a focused ion beam and then examined with electron microscopy and different diffraction methods.

Pokroy and colleagues also show that the shape of the droplets, and thus the curvature of the single crystals, can be controlled by adjusting parameters such as the oxygen partial pressure in the environment during the annealing step.