Transmission electron microscopic studies were made of the central portion of tetrapod-shaped oxide particles which had been produced by oxidizing Zn vapor in air. This revealed that there existed trigonal-pyramid crystals other than the leg crystals at the center. Scanning electron microscopy of fractured particles revealed characteristic faceted fracture surfaces. The results supported the view that the crystals grew from an inversion-type octa-twin embryo.

Some Evidence for the Octa-Twin Model of Tetrapod ZnO Particles. Iwanaga, H., Fujii, M., Ichihara, M., Takeuchi, S.: Journal of Crystal Growth, 1994, 141[1,2], 234-8