A variety of novel ZnO nanostructures such as nanowires, nanowalls, hierarchical nanostructures with 6-, 4-, and 2-fold symmetries, nanobridges, nanonails have been successfully grown by a vapor transport and condensation technique. Doping both In and Sn into ZnO hierarchical nanostructures can be created. The 2-fold eutectic ZnO structures can also be created without any doping in the source. It was found that the hierarchical nanostructures can be divided into two categories: homoepitaxial and heteroepitaxial where heteroepitaxy creates the multifold nanostructures. The novel ZnO nanowalls and aligned nanowires on a-plane of sapphire substrate have also been synthesized and the photoluminescence is studied. The ZnO nanowires also demonstrated very good field emission properties, comparable to carbon nanotubes. These nanostructures may find applications in a variety of fields such as field emission, photovoltaics, transparent EMI shielding, supercapacitors, fuel cells, high strength and multifunctional nanocomposites, etc. that require not only high surface area but also structural integrity.

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