Precursor-controlled synthesis of different ZnO nanostructures by the hydrothermal method

Versatile ZnO nanostructures have been fabricated by a two-step hydrothermal method. Controllable growth of ZnO is feasible by using different kinds of zinc sources. It is revealed by scanning electron microscopy that ZnO nanorods with average diameter 155 nm were synthesized by using Zn(CH ₃COO)₂ as the zinc source_. As for the situation when Zn(NO₃)₂ was used, taper-like ZnO nanostructure with large aspect ratio was formed. In particular, two-dimensional ZnO nanosheets can be fabricated when ZnCl₂ was introduced and the distinctive X-ray diffraction spectrum indicates that the anisotropic growth of ZnO along its <0001> direction was hindered, which was caused by the attraction of Cl^- ions onto the ZnO polar face instead of growth units. Consequently, the anisotropic growth of ZnO along this direction was hindered, while the other two samples were vertically aligned against the substrates, which can be deduced from their sharp and strong ZnO (002) diffractions. Additionally, their optical properties including the absorptions of ultraviolet light and the corresponding optical bandgaps were also measured by an ultraviolet-visible spectrometer, which changed with the structural transformations. All these properties make them feasible for applications in the fields of both solar cells and biosensors.