Hierarchical structured nanohelices of ZnS.

Wurtzite-structured materials, such as ZnO, ZnS, GaN, and AlN, have an important characteristic: the presence of polar surfaces that result from cationor anion-terminated atomic planes. Consequently, a series of novel nanostructures, such as nanosprings, nanorings, nanohelices, and nanobows, have been formed. The mechanism that drives the formation of these novel configurations minimizes the electrostaticinteraction energy of the polar surfaces. As of now, these nanostructures have been mainly observed for ZnO, although nanosprings of wurtzite-structured AlN and rutile-structured SnO2 [3] have also been observed as a result of the same formation mechanism. ZnS, as another member in the wurtzite family and one of the most important materials in photonics, is a direct wideband-gap (3.91 eV) semiconductor with a high index of refraction and a high transmittance in the visible range. As for one-dimensional nanostructures, ZnS has been synthesized as nanowires, nanobelts, nanotubes, and nanocombs. Recently, ZnS nanobelts have been doped with manganese, by post-annealing, without changing the crystallography of the ZnS nanobelts. Optically pumped lasing has also been shown in single ZnS nanobelts. Herein, we report for the first time the high-yielding synthesis of hierarchical structured ZnS nanohelices. The morphology of the ZnS nanohelix is more complex than that observed for ZnO. The mechanism and the process of formation of the hierarchical structure are presented on the basis of the structural information provided by electron microscopy analysis. It is concluded that the hierarchical structure is a combined result of several growth features in the wurtzite ZnS. The synthesis is based on the vapor deposition process. The as-synthesized samples were analyzed by using X-ray diffraction (XRD) and scanning electron microscopy. The XRD data confirmed that the as-synthesized sample was wurtzite ZnS. Optically, it appears yellow–white and covers the silicon deposition substrate. The synthesized material has a relatively high yield on the substrate and shows a high degree of reproducibility. The deposited material has a dominant morphology, which consists of helices of a ZnS