Growth of vertically aligned single crystal ZnO nanotubes by plasma-molecular beam epitaxy

Highly oriented and vertically aligned single crystalline ZnO nanotubes were fabricated on Al2O3 (0001) substrates by plasma-molecular beam epitaxy without employing any external metal catalysts or templates. Field emission scanning electron microscope images indicate that the regularly aligned ZnO nanotubes with uniform size distribution were obtained. The chimney-like single crystal ZnO nanotube was confirmed by the transmission electron microscope and selected area electron diffraction pattern of the single nanotube. The formation mechanism of the nanotubes was also described briefly.