The nanonail flower

The excellent physical and optical properties of ZnO make its nanostructures suitable for various device applications, including in optoelectronics, nanophotonics, piezotronics, sensing, and solar cells, among others. ZnO is a wide bandgap (3.4 eV) semi-conductor which is transparent in the visible range. The growth process of such a structure can be described as two steps. First, a nanorod grows along the axis by alternatively staking O and Zn atomic layers over the top facet; Second, the growth along the axial direction slows down and the radial growth starts to become dominant, leading to the formation of a hexagonally shaped nanonail head. Hence, there was a change in growth conditions that suddenly hastened the radial growth to gradually thicken the nanorod while the epitaxy over top facet continued.