Synthesis of ZnO/cubic (Zn, Mg)O heterostructure nanorods

ZnO/cubic (Zn, Mg)O core–shell heterostructure nanorods with wire-shaped tips have been synthesized via a catalyst-free thermal evaporation process on Si substrates. The average diameters were about 180 nm for nanorods and about 20 nm for tips. Transmission electron microscopy (TEM) investigations revealed that the tip was a single-crystalline cubic structure and grew along the [2 0 0] direction. A two-step growth process was used to synthesize the ZnO/(Zn, Mg)O heterostructure nanorods; that is, Zn and Mg powders were first evaporated at 630 °C and then the temperature was raised to 750 °C. High-resolution TEM and energy dispersive x-ray spectroscopy analysis confirmed that the product is pure ZnO at the first step. X-ray diffraction, photoluminescence and TEM results indicated that a final heterostructure nanorod consisted of a wurtzite ZnO core and a cubic (Zn, Mg)O shell. The growth temperature and process control were suggested to be responsible for the formation of heterostructure nanorods.