Solvothermal Synthesis And Characterization Of Zinc Selenide And Zn-Doped Cadmium Selenide Nanocrystals

In recent years, semiconductor nanomaterials is one of the most active areas due to their distinguished optical and electronic properties that are different from those of their bulk counterparts. Properties of nanoparticles not only have relation with their sizes but also their shapes. How to control the shapes of nanoparticles effictively is still a tough problem. Nanostructures are structures that defined as having at least one dimension between 1 and 100 nm while microstructures are between 1 and 100μm. Ever since 1980s, nano/microstructures have received steadily growing interests due to their excellent properties and potential applications superior to their bulk counterparts. Metal chalcogenides are rather interesting materials. 3D metal selenide nanomaterials can exhibit special optical and electrical properties compared with semiconductor quantum dots. Therefore, the controllable synthesis of 3D metal selenide nanomaterials is of great importance.In this thesis, solvothermal method was employed to the preparation of novel morphological metal selenide nanomaterials, such as nano/microflowers, nanoflakes and nanorods. The formation mechanisms of different morphologies are analyzed. The as-obtained products were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive spectrum (EDS) and UV-vis absorption spectroscopy. The finished main work has three main aspects as follows:1. Solvolthermal Synthesis and Characterization of paniculiform-like ZnSe MicrostructuresPaniculiform-like Zinc Selenide (ZnSe) microstructures have been successfully prepared by sovolthermal method using diethanolamine as solvent at 140℃for 24 h. The novel three-dimensional paniculiform-like microstructures were found with six petals and in excellent symmetry. SEM indicated that every single petal is about 3μm in length and the diameter of the root is 2μm. XRD analysis revealed the paniculiform-like microstructures were composed of layers and the crystal structure of the layers was hexagonal phase. The results also showed that diethanolamine molecules play a crucial role in the formation of paniculiform-like ZnSe microstructures. The effects of the reaction time and addition agents on the products were investigated, respectively.2. Solvolthermal Synthesis and Characterization of Zn-doped CdSe (Cd1-xZnxSe, x = 0.1-0.3) nanoflakesThe products composed of acantho-Cd0.9Zn0.1Se nanoflakes with the thickness of 20 nm were synthesized via solvothermal treatment of the precursor in en at 180℃for 12 h. when all the other conditions were the same as above one but the heating time was added to 24 h, chrysanthemum-like Cd0.9Zn0.1Se nanoflakes with the thickness of 50 nm were obtained. XRD analysis revealed the crystal structure of Cd1-xZnxSe (x = 0.1-0.3) nanoflakes was hexagonal wurtzite phase. Compared with the absorption peak (690 nm) of CdSe, it can be seen that the absorption peaks of Cd1-xZnxSe (x = 0.1-0.3) nanoflakes are monotonous blue-shifted with increasing Zn content. The effects of molar ratios of reactants and addition agents of solvents on the products have been investigated, respectively.3. Solvolthermal Synthesis and Characterization of Zn-doped CdSe (Cd1-xZnxSe, x = 0.1-0.3) nanorodsUsing the corresponding mixed-metal precursors, hexagonal phase Cd1-xZnxSe (x = 0.1-0.3) nanorods have been successfully synthesized via subsequent solvothermal decomposition in hydrazine hydrate at 180℃for 12 h. The products composed of pine-like Cd0.9Zn0.1Se nanorods with the length of 50-100 nm were synthesized via solvothermal decomposition of the corresponding precursor (x = 0.1). Cd0.8Zn0.2Se nanotrees structures consisted of branched nanorods with the length of 100-200 nm were synthesized via solvothermal treatment of the precursor (x = 0.2). When x values increased to 0.3, branched Cd0.7Zn0.3Se nanorods with the length of 200-300 nm were obtained. XRD analysis revealed the crystal structure of Cd1-xZnxSe (x = 0.1-0.3) nanorods was hexagonal wurtzite phase. Compared with the absorption peak (690 nm) of CdSe, it can be seen that the absorption peaks of Cd1-xZnxSe (x = 0.1-0.3) nanorods are monotonous blue-shifted with increasing Zn content. The effects of solvents on the products were investigated.