Zinc-oxide nanostructures are grown without using a metal catalyst by forming a seed layer of polycrystalline zinc oxide on a surface of a substrate. The seed layer can be formed by an atomic layer deposition technique. Growth of at least one zinc-oxide nanostructure is induced on the seed layer. The seed layer can alternatively be formed by using a spin-on technique, such as a metal organic deposition technique, a spray pyrolisis technique, an RF sputtering technique or by oxidation of the seed layer.