SEM images of hierarchical ZnO nanostructures with basic 6-fold (first row), 4-fold (second row), and 2-fold (third row) symmetry made by thermal vapor transport and condensation technique. The primary core nanowires are either pure In2O3 or In2O3-doped ZnO, whereas the secondary branch nanowires are pure ZnO.

Z. Ren, J. Lao, and J. Wen. Nano Lett. 2(11) (2002).

Image courtesy: Dr. Z. Ren, Boston College.