Nucleation and Growth of Catalyst-Free Zinc Oxide Nanostructures

This paper deals with the investigations on the nucleation and growth of Zinc Oxide (ZnO) nanostructures in a catalyst free synthesis. The ZnO nanostructures have been formed by evaporation of Zn (99.99%) in O₂ and Ar atmosphere in single zone furnace under two temperature regions, region A (∼1173–1073 K) and region B (∼873–773 K). Through application of XRD and TEM techniques, it has been shown that first ZnO is formed which changes to ZnO _x through creation of oxygen vacancies. The ZnO _x acts as self-catalyst and leads to formation of various nanostructures. Those observed in the present investigation are nanotetrapods (1D, diameter ∼ 70–450 nm, length ∼ 2–4.5 m) nanorods (1D, diameter ∼ 45–95 nm, lengthz ∼ 2.5–4.5 μm), nanoflowers(2D, central core diameter ∼ 90–185 nm, length of petals/nanorod ∼ 1.0–3.5 μm) and nanoparticles (3D, size ∼ 0.85–2.5 μm). These nanostructures have been revealed by SEM explorations. Attempts have been made to explain the formation of the various nanostructures in terms of the creation and distribution of the ZnO _x , the temperature as well as oxygenation conditions.