Preparation, Modification And Self-Assembly Of Nano-Particles Used For Photonic Crystal And Its Optical Property

Photonic crystal material is one of the hotspots in material research. It is a kind of materials with regular periodicity of dielectric structures, which has the ability to manipulate, confine, and control light. So photonic crystal becomes the frontier of functional materials.The method to prepare photonic crystal is to arrange in order using two or more different materials with uniform morphology. The 3D photonic crystal with near-infrared region forbidden band-gap has already been fabricated by Precision Process, such as layer-by-layer etch. The defects of this method is expensive and complex systems. Self-assemby method is an easy way to fabricate photonic crystal with near-infrared or shorter wave regioin photonic band-gap. As we know, SiO₂ particles and polystyrene particles which meet the requirements of photonic crystal are easy to be prepared under reaction condition control.The photonic crystal assembled by SiO₂ particles possesses the near-infrared and visible region photonic band-gap, but there are two defects. One is that the relative value of dielectric constant contrasted with medium is small, another is unperfect arrangement of SiO₂ particles which result in accident defect. The materials with high refractive index, such as ZnO, CdS and ZnS, possess high relative value of dielectric constant and widen the range of periodicity Dielectric function. Additionally, enhancement the surface charge of SiO₂ particles assembled for photonic crystal is a effective way to reduce the accident defects in the photonic crystal.The thesis worked on the preparation of structure unit which was used to self-assemble photonic crystal. The unit contained ZnO, CdS, ZnS and SiO₂ particles. The morphology of ZnO particles was controlled by the reaction temperature, the reactant concentration and the pH value. The deep research indicated the mico-structure feature of ZnO particles with various morphology possessed the same structure. On this basis, the photoluminescence property and the mechanism were researched.The thesis worked on the preparation of spherical CdS and ZnS particles by wet chemical synthesization assisted by ultrasonic, too. The crystal structures and morphologies were researched. And the effect of ultrasonic during synthesization was researched.Additionally, we prepared SiO₂ particles by Stober method and modified this method by electrolyte NaCl to enhance the surface charge, which improved the property of self-assembly SiO₂ particles. And another method, surface modification by succinic acid, was used again for the same purpose. Finally, the SiO₂ opal photonic crystal was fabricated by vertical deposition method and the optical properties were researched.The results were listed:1) The various morphologies ZnO particles, including taper-like, dumbbell-like, spherical, rugby-like, dart-like and flower-like, were prepared by control of reaction temperature, reactant concentration and pH value by wet chemical synthesization assisted by ultrasonic. As research model, the micro-structure of rugby-like ZnO particles were researched. We found out that the single crystal structure was created in the center of ZnO particles, a great number of micro-twins were formed around the center, and polycrystal was formed on the fringe. The defect layers was the key of morphology of ZnO particles and then ZnO particles grew along [0001] direction. Base on the structure research, we suggested a new mechanism on the preparation of ZnO particles. And then the effects of temperature, pH value and reatant concentration were researched. At last, the photoluminescence property of ZnO particles was researched and we found out that the defects was the key of photoluminescence property of ZnO particles.2) The spherical CdS and ZnS particles were prepared by chemical synthesization assisted by ultrasonic. SEM images showed that the morphologies of CdS and ZnS particles were spherical and the sizes ranged from 150-500 nm. XRD test indicated that CdS particles possessed wurtzite structure of the six-party. Otherwise, ZnS particles possessed cubic structure.3) SiO₂ particles were prepared by St(o|¨)ber method, which the sizes ranged from 300-800 nm and The relative standard deviation was less than 5%. In order to improve self-assembly ability, the traditional St(o|¨)ber method was modified. The tlectrolyte NaCl was added during process to enhance the surface charge of SiO₂ particles. We found out that the surface charge of SiO₂ particles were enhanced after NaCl had been added. Moreover, the size of SiO₂ particles is larger. Zeta potential of SiO₂ particles enchanced from 48.7 mV to 56.6 mV, and the size become large from 315 nm to 380 nm. When the quantity of NaCl added is in a certain range, the size of SiO₂ particles become large with NaCl added. However, beyond the scope of this, double-size SiO₂ particles happened. Research showed that there was no effect to optical properties of photonic crystal assembled by SiO₂ particles modified by NaCl. Additionally, the optical properties were only effected by the size of SiO₂ parcles.4) In order to enhance surface charge of SiO₂ particles, they were modified by Organic. Succinic acid was modifier and acetonitrile was solvent. One carboxyl of the succinic acid reacted with the -OH on the surface of the SiO₂ particles and the product is carboxylate. Zeta potential proved that the surface charge of SiO₂ particles was enhanced after they had been modified.5) We attempted to prepare CdS@SiO₂ nucleus-shell particles by chemical deposition. Results showed that a little CdS deposited on the surface of SiO₂ particles, but the quantity is very small.