Dopant induced shape evolution of colloidal nanocrystals: The case of zinc oxide

The electrical, optical and other important properties of colloidal nanocrystals are determined mainly by the crystals´ chemical composition, size and shape. The introduction of specific dopants is a general approach of modifying the properties of such nanocrystals in well-controlled ways. Here we show that in addition to altering the atomic composition of the nanocrystals the introduction of specific dopants can also lead to dramatic changes in morphology. The creation of Mg doped ZnO nanocrystals by an ester elimination method provides an excellent example of this procedure: depending on the molar ratio of dopant precursor in the reagents, nanocrystals with well defined shapes, from tetrapods to ultrathin nanowires, which exhibit tunable optoelectronic properties, are obtained in a one-step reaction. We find that the Mg dopant plays an important role in the primary nucleation stage, resulting in seeds possessing either zincblende or wurtzite structures, which is critical for the growth of nanocrystals with different shapes. We demonstrate that this method can be extended to other oxide nanocrystal systems and provides an attractive and effective strategy for creating doped nanocrystals with interesting compositional and spatial complexity. Exquisite control of the doping procedure we have developed is a promising avenue to controlled synthesis of nanocrystals with exactly defined compositions, specifically tailored shapes and advanced materials properties.