  This paper deals with the investigations on the nucleation and growth of ZnO
nanostructures in a catalyst free synthesis. The ZnO nanostructures have been
formed by evaporation of Zn (99.99%) in O_2 and Ar atmosphere in single zone
furnace under two temperature regions, region A (~1173-1073K) and region B
(~873-773K). Through application of XRD and TEM techniques, it has been shown
that first ZnO is formed which changes to ZnOx through creation of oxygen
vacancies. The ZnOx acts as self-catalyst and leads to formation of various
nanostructures. Those observed in the present investigation are nanotetrapods
(1D, diameter ~ 70-450nm, length ~ 2-4.5mm) nanorods (1D, diameter ~ 45-95nm,
length ~ 2.5-4.5mm), nanoflowers(2D,central core diameter ~ 90-185nm, length of
petals/nanorod ~ 1.0-3.5mm) and nanoparticles (3D, size ~ 0.85-2.5mm). 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 ZnOx, the temperature as well as oxygenation
conditions.
