Optimisation on the growth and alignment of ZnO nanorods

Synthesis of aligned ZnO nanorods (NRs) is important for electronic and optoelectronic devices. In this work we demonstrate the growth of ZnO nanorods by co-precipitation method using zinc nitrate and hexamine precursors. The samples were characterized by X-ray diffraction analysis and Scanning electron microscopy. It is observed that the seed substrates offer nucleation sites (seeds) for one-dimensional growth of ZnO nanorods. ZnO nanorod array grown on successive ionic layer adsorption and reaction (SILAR) seed layer were found to be irregular and non-uniform due to the etching of the seed substrate by growth solution. However, dip-coated seed substrate yielded uniform growth of ZnO nanostructures. ZnO nanostructures with flower-like morphology were obtained for pH of 9. On reducing the pH the flower morphology transformed into rod-like morphology with rod diameter of about 200 nm. Reducing the pH further to 3, the diameter of the nanorods is decreased to about 20 nm. On reducing the precursor concentration, the faceted morphology of the nanorods is changed into needle-like shape (with sharp tips) along with reduction in diameter (about 20 nm). The growth of uniform and vertically aligned ZnO nanorods is observed in dip-coated seed substrate with 5 pH. The results indicate that the diameter of ZnO nanorod array could be controlled by varying the precursor concentration.