Polystyrene-microsphere-assisted patterning of ZnO nanostructures: growth and characterization.

In this work, periodic arrays of various ZnO nanostructures were fabricated on both Si and GaN substrates via a facile hydrothermal process. To realize the site-specific growth, two kinds of masks were introduced. The polystyrene (PS) microsphere self-assembled monolayer (SAM) was employed as the mask to create a patterned seed layer to guide the growth of ZnO nanostructures. However, the resulting ZnO nanostructures are non-equidistant, and the diameter of the ZnO nanostructures is uncontrollable. As an alternative, TiO2 sol was used to replicate the PS microsphere SAM, and the inverted SAM (ISAM) mask was obtained by extracting the PS microspheres with toluene. By using the ISAM mask, the hexagonal periodic array of ZnO nanostructures with high uniformity were readily produced. Furthermore, the effect of the underlying substrates on the morphology of ZnO nanostructures has been investigated. It is found that the highly ordered and vertically aligned ZnO nanorods epitaxially grow on the GaN substrate, while the ZnO nanoflowers on Si substrates are random oriented.