  Complex hierarchical shapes are widely known in biogenic single crystals, but
growing of intricate synthetic metal single crystals is still a challenge. Here
we report on a simple method for growing intricately shaped single crystals of
gold, each consisting of a micron-sized crystal surrounded by a nanoporous
structure, while the two parts comprise a single crystal. This is achieved by
annealing thin films of gold and germanium to solidify a eutectic composition
melt at a hypoeutectic concentration (Au-enriched composition). Transmission
electron microscopy and synchrotron submicron scanning diffractometry and
imaging confirms that the whole structure was indeed a single crystal. A
kinetic model showing how this intricate single-crystal structure can be grown
is presented.
