Controlled Synthesis And Mechanism Investigation Of Metal Chalcogenide Semiconductor Nano Compounds Through Wet-Chemical Methods

Binary metal chalcogenide semiconductors have attracted much attention due to their unique physical, chemical properties and the widely applications in many fields, such as electronics, magnetics, optics, etc. If applied as basic building blocks, they also play an important role on the properties of assembling nano-/micro- apparatus. Therefore, it was important to investigate the structures, morphologies and synthetical technologies of nano semiconductors. As typical materials of binary semiconductors, copper chalcogenides (e.g. Cu2O, copper sulfide and copper selenide), ZnO and lead chalcogenides (e.g. PbS, PbSe and PbTe) have attracted considerable attention owing to their wide applications in catalysts, photoelectric transition, luminescence, piezoelectricity, gas sensor, thermoelectricity materials, etc. It was well known that the properties of materials were mainly determined by composition, structure of crystal itself according to previous studies, however, the size and shape of materials also played important roles to determine their applications and properties. Thus, controlled synthesis on the size and shape of nano-semiconductors will largely increased their scientific significances and widen the corresponding technical applications. In this study, we managed to produce Cu2O nanocrystals with uniform shapes via facile and warmly wet-chemical methods, and then transferred Cu2O nanocrystals into Cu7S4 and Cu2-xSe with novel hollow polyhedral morphologies. In addition, we prepared ZnO nanorod of small diameter (<10nm) with varied aspect ratio in ethanol solution under ambient temperature condition or low temperature hydrothermal condition. In the end, dendrites of lead chalcogenides (PbS, PbSe and PbTe) were synthesized by microwave-assistant heating routes. The main contents of this dissertation could be summarized in four sections:1. Shape- and size-controlled synthesis of Cu2O nano-/ micro-crystals.Cubic, octahedral, sphere-like and fiber-like of Cu2O particles have been prepared under different reaction conditions. The shape and size of Cu2O particles were strongly dependent on different reaction parameters, for example, the precursor's concentration, the type of reductive regent, the concentration of PVP and NaOH, even the mixing sequence of reaction component.2. The synthesis of copper sulfide and copper selenide nano/micro hollow cages with uniform polyhedral and sphere shapes.Firstly, hollow single-crystal semiconductor of Cu7S4 with high symmetric 18-facet polyhedron structure was prepared by reacting cubic Cu2O template with Tu. Then, 18-facet polyhedra of Cu7S4 with hollow window structure and various sizes were synthesized at high temperature hydrothermal condition. Finally, cubic-like, octahedral-like and sphere-like Cu2-xSe hollow cages were successfully fabricated from shape-controlled Cu2O as sacrificial cores, precursors or templates by a single technique at room temperature. A plausible formation mechanism of these hollow structures could be based on the Kirkendall effect. These studies were published by JACS and Chem. Commun. The reviewers of JACS gave high comments about the study of Cu7S4 polyhedron."The authors present valuable results of an original research in the area of chemical synthesis of functional materials, and I believe this paper fell within top 20% in this field."3. Preparation of ZnO nanorods with various aspect ratios.We studied the reactive time and concentration effect on morphologies of ZnO nanorods at room temperature. It was found that the aspect ratio would be increased if the reactive time was prolonged or the reactant concentration was increased. The optical properties showed that the ZnO nanorods possess perfect crystalline structure. We also discussed the effect of different solvent, reactive temperature and reactant ratio on morphologies of ZnO nanorods.4. Dendrites of lead chalcogenides (PbS, PbSe and PbTe)Dendrite of PbS with 3-D structure was synthesized by microwave assistant heating method in EG solution. It was found that the formation of PbS was dependent on the kinetics condition, and the precursor concentration also played an important role on the morphologies of PbS. The cubic or plate-like PbS nanoparticles would be obtained if low concentration of precursor was used. The transferred process from cube to dendrite of PbS would be clearly observed when increasing the concentration of precursors. We also synthesized the dendrites of PbSe and PbTe if Se and Te powder replaced sulfur source and another reducing agent was added in this system.