In summary, we have determined optimum experimental conditions for preparing ZnO nanostructures having hexagonal nanorods on the ZnO seed layers and nanoflowers on the ZnO nanorods in
three consecutive steps, such as a synthesis of a sol–gel solution (Step I), a fabrication of ZnO seed layers (Step II), and a ZnO nanostructure growth using a hydrothermal method (Step III)