Morphology And Size Control Of Silver Oxide, Silver And Cuprous Oxide Micro-/nano-particles

Anisotropy is one of the most basic properties of crystals. Different crystal surfaces or directions may exhibit different physical and chemical properties. Furthermore, the properties of materials in nano-scale could depend on their sizes and be very different from those of their corresponding bulk ones. Therefore, the controllable preparation of nanocrystals with different exposed surfaces and size is very important and challenging.This thesis aimed to the synthesis of some important semiconductor and metallic materials based on the crystal growth theory, and explored the nature and mechanism of the growth of these materials. The major results can be summarized as follows:1. Ag₂O micro-/nano-particles were successfully prepared by using silver nitrate, ammonia and sodium hydroxide as raw materials under a solution synthesis. The structures, shapes and sizes of the Ag₂O were characterized systematically by using XRD, SEM, TEM, etc. The shapes were tuned from octahedron to truncated octahedron and then to cube by decreasing the reaction concentration, the size of silver oxide particles were found to decrease accordingly. Furthermore, complicated polyhedron-based branching particles can be controlled by changing the concentration of sodium hydroxide. A preliminary mechanism based on the anion coordination polyhedra were proposed to explain the morphologic changes of the Ag₂O nanostructures.2. Cuprous oxide micro- and nano-crystals were successfully prepared by reducing copper nitrate with potassium borohydride(KBH₄) using poly(vinyl pyrrolidone) (PVP) as the surface regulator. The structures, shapes and sizes of the Cu₂O micro- and nano-particles were characterized systematically by using XRD, SEM, TEM, HRTEM etc. The shapes of cuprous oxide particles were modified with the concentration of PVP. Furthermore, it is found that the size of cuprous oxide particles can be easily decreased by simply reducing the concentration of reactant. 3. Silver nanoplates and silver multiple twinned particles (MTPS) were prepared by reducing silver nitrate with poly(vinyl pyrrolidone) (PVP). It is found that the silver nanoplates were formed at the room temperature. By analyzing the selected area electron diffraction(SAED) pattern, we concluded that the silver plates are in fact imperfect crystals, where exists a lot stacking fault. When the reaction temperature increased, the silver nanostructures were found to change to MTPS, which can be explained as that the stacking faults decrease with the increase of the reaction temperature.