Controllable Growth Of Low Dimensional II-VI Semiconductor Nanostructures

The controllable growth of low dimensional semiconductor nanomaterials is the frontiers and the focus in the field of nanoscience and nanotechnology. In the present work, the typical II-VI semiconductor nanostructures have been synthesized by using electrodeposition and wet chemical methods. The size, composition, crystal structure, and growth orientation have been successfully controlled.Highly ordered wurtzite ZnS nanowire arrays have been prepared at a low temperature of T = 120 oC by employing electrochemical deposition techniques using the porous alumina membrane with 40 nm diameter pores as template. ZnS single-crystal nanowire arrays with [110] growth direction have been obtained at an extremely low current density of 0.1 mAcm^-2. At higher current densities, the deposited ZnS nanowires possess a polycrystalline structure. The nanoscale confinement is found to be favorable for the growth of wurtzite ZnS single crystals.Hexagonal CdS nanowire arrays have been prepared at a low temperature of T = 110 oC by employing electrochemical deposition techniques using the porous alumina membrane as template. It has been found that the deposition current density has important effect on the growth orientation of the deposited nanowire arrays. At higher current densities of 1.28 mAcm^-2, the deposited CdS nanowires possess a polycrystalline structure. An extremely low current density of 0.05 mAcm^-2 is favorable for the growth of single-crystal CdS nanowires along the normal direction of the intrinsic low-surface-energy (103) face. According to the classical theory of nucleation and growth for electrocrystallization, a quasi-two-dimension critical dimension model has been proposed, which shows that the critical dimension is dependent on the electrodeposition parameters, the surface energy of the formed crystal face, and the lattice misfit between the nanowires and substrate. The formation of electrodeposited single-crystal nanowires and the formation mechanism of various growth orientations can be well understood by employing the suggested model.Porous alumina templates with average diameter of ²5 nm, 40 nm, and 120 nm were obtained under selected anodizing conditions. Highly ordered hexagonal CdSe nanowire arrays have been successfully yielded by employing the electrodeposition technique using the porous alumina as templates. We demonstrate by experimental and theoretical efforts that the growth orientation of the CdSe nanowires can be effectively manipulated by varying the nanopore diameter of the templates. The preferential orientation of CdSe nanowires changes from [001] direction to the [101] and [103] directions at a critical diameter D0 in the range of 40-120 nm at the current density I = 1.28 mAcm^-2. At an extremely low current density I = 0.06 mAcm^-2, the preferential orientation of CdSe nanowires switches from [101] direction to [103] direction as D≥40 nm. The diameter-dependent orientation can be understood based on the total energy minimum principle. The electrodeposited CdSe nanowires present tunable optical properties by varying their structural characteristic and growth orientation.Multiwalled carbon nanotube (MWCNT)/CdS core/shell heterostructures have been synthesized via a simple solution-phase method. The thickness of CdS shells can be facilely tuned by either the reaction temperature or time. The CdS nanoparticles are first formed directly on the activated sites of the MWCNT surface, and then a uniform CdS sheath is yielded via orientated aggregation processes.Using the ZnO nanoneedles as self-sacrificed templates, ZnO/ZnS core/shell and ZnS hollow nanoneedles have been synthesized via a surfactant-free method. At a low temperature hydrothermal condition (90 oC), ZnO/ZnS core/shell nanoneedles were formed through in-situ chemical reaction between the ZnO template and sulfide source. The ZnS hollow nanoneedles are yielded via nanoscale Kirkendall effect at an elevated temperature (120 oC). If the obtained hollow nanoneedles are employed as the starting materials, fantastic nanoarchitectures could be realized by employing the Rayleigh instability. These novel nanostructures may find important application in nanodevices.