Self-assembled urchin-like ZnO nanostructures fabricated by electrodeposition-hydrothermal method

We report the urchin-like ZnO nanostructures composed of self-assembled cone-shaped ZnO nanorods grown on the Zn-deposited Cu substrate fabricated by electrodeposition-hydrothermal method. In the FESEM images, the cone-shaped ZnO nanorods radiate from the center of the nanostructure forming a spherical urchin-like shape with a diameter of 5 μm-10 μm, the average diameter and the length of the cone-shaped ZnO nanorods can be identified as 0.1 μm-1 μm and 3 μm-5 μm, respectively. The SAED of the diffraction ring suggests that this ZnO nanorod was polycrystalline with the wurtzite hexagonal phase. The measured optical band gap Eg values are 3.12 eV, 2.98 eV, 3.04 eV and 3.10 eV respectively with the increasing pH values. In the as-prepared condition, the photoluminescence (PL) spectra of the urchin-like ZnO nanostructures are composed of a violet emission band at about 393 nm and two blue emission bands at about 446 nm and 463 nm at room temperature. With an increase in the pH value of hydrothermal solution, the intensity of PL spectra increases, while the forbidden gaps of four samples become narrower. Finally, a possible growth mechanism of the urchin-like ZnO nanostructures has been discussed.