Flower-like ZnO with various morphologies on ZnO nanorod arrays have been hydrothermally fabricated using zinc substrates at low temperature (70 degrees C). The time-dependent experiments indicated that both dense ZnO nanorod arrays and flower-like ZnO were created when the reaction time is 30 min. A growth mechanism was proposed to account for the growth of the flower-like ZnO on ZnO nanorod arrays. In situ growth caused the generation of dense ZnO nanorod arrays that were almost perpendicular to the surface of a zinc substrate. Due to the different rate of nucleation and crystal growth the morphology of flower-like ZnO on the top of ZnO nanorod arrays varied with the concentration of OH-. The ionic radius of alkali metal hydroxide used to generate Zn(OH)(4)(2-) ions greatly affected the morphology of ZnO. Owing to the small quantity of ZnO nuclei and Zn(OH)(4)(2-) the flower-like ZnO on ZnO nanorod arrays became fewer when lowering the concentration of Zn2+ and OH- while keeping the ratio between them. (c) 2012 Elsevier B.V. All rights reserved.