Controlled synthesis and size-dependent polarization domain structure of colloidal germanium telluride nanocrystals.

Germanium telluride (GeTe) exhibits interesting materials properties, including a reversible amorphous-to-crystalline phase transition and a room-temperature ferroelectric distortion, and has demonstrated potential for nonvolatile memory applications. Here, a colloidal approach to the synthesis of GeTe nanocrystals over a wide range of sizes is demonstrated. These nanocrystals have size distributions of 10-20% and exist in the rhombohedral structure characteristic of the low-temperature polar phase. The production of nanocrystals of widely varying sizes is facilitated by the use of Ge(II) precursors with different reactivities. A transition from a monodomain state to a state with multiple polarization domains is observed with increasing size, leading to the formation of richly faceted nanostructures. These results provide a starting point for deeper investigation into the size-scaling and fundamental nature of polar-ordering and phase-change processes in nanoscale systems.