Transmission electron microscopy study on the growth of zinc oxide crystals under hydrothermal conditions

ZnO crystals were grown in the presence of ZnO nanorod seeds under hydrothermal conditions while the same location on the ZnO nanorod was repeatedly observed by transmission electron microscopy. The surface of the ZnO seed crystal was covered with an amorphous layer during the early stages of crystallization (0.5–1.5 h). This amorphous layer was subsequently transformed into nanocrystals after 3.0 h. Finally, after 5.0 h, ZnO seeds suddenly grew preferentially in the [001] direction. These results suggest that the formation process of an amorphous ZnO layer on the surface of the seed crystals and its subsequent crystallization plays an important role in the induction of further crystal growth of ZnO nanorods.