Integration of ZnO nanotubes with well-ordered nanorods through two-step thermal evaporation approach

We have successfully realized the integration of ZnO nanotubes and well-ordered nanorods through a simple two-step thermal evaporation of Zn powder without any metal catalyst. Detailed structural analysis shows that the step-one prepared samples at the low substrate temperature are composed of hexagonal-shaped Zn/Zn suboxide nanowires dominated by Zn with little oxidation via the layer-by-layer growth mechanism. In the second step, by heating the step-one deposited samples and Zn powder at high temperature, highly ordered single-crystalline ZnO nanorods were epitaxially grown on the surface of nanowires through the screw dislocation growth mode. Simultaneously, Zn inside the nanowires sublimates to form hollow ZnO nanotubes, which finally results in the formation of ZnO nanotubes surrounded by well-ordered nanorods (ZNSWN). The field-emission scanning electron microscopy images of samples with different heating times indicate that the length of ZnO nanorods in the tube walls can be well controlled by changing the reaction time with a growth rate of similar to 3 nm/min. We also further present the comparative X-ray diffraction, Raman, and photoluminescence investigation for the growth process and structural information of the fabricated ZNSWN nanostructures.