Design And Self-assembly Of Binary Metamaterial Structures

Metamaterials can be prepared by precision process and self-assemblyMethod. The application of precision process is limited for its defects ofexpensive equipment and complex process. The self-assembly of colloidalnano-，submicro-or micro-spherical particles is a useful technique for obtainingcolloidal crystals with close-packed crystal structures. Most of the researcheshave focused on the preparation of colloidal crystals composed of single-sizespheres, and the obtained structures are limited to face-centered cubic （fcc） orhexagonal close-packed （hcp） structures. Since the first discovery of binarysuperlattice in native Brazilian opal, synthesis of binary metamaterial structureshas gained growing interest.The application of metamaterials self-assembled by SiO₂is limited for thestructure defects and low dielectric constant of SiO₂colloidal spheres. Withincreasing the surface charge of SiO₂colloidal spheres, the defects ofmetamaterials decrease which can improve the performance of metamaterials.Metamaterial heterostructures which contain the materials with high refractiveindex widen the range of periodicity dielectric function that could provide newperformances.The thesis worked on the preparation of silica particles with different sizedistributions and surface morphologies by St ber methods with different mixingprocesses. The comparison of three st ber methods was investigated. Thereaction conditions including TEOS and NH3concentrations and the formationmechanism of particles were also investigated. The silica spheres were modifiedby electrolyte NaCl to enhance the Zeta potential. The effects of NaClconcentration on the morphology, size and Zeta potential were discussed.Single-size silica colloidal crystals were synthesized by vertical depositionmethod, dual substrates method and electrophoresis-assisted self-assembly. The morphology, structure and defects of colloidal crystals were investigated. Theeffects of processes, surface charge, calcination temperature, voltage and Zetapotential on the morphology of colloidal crystals were discussed. The LS₂、LS₄、LS₆and LS_xbinary metamaterial structures were designed and calculated. Andseveral binary metamaterial structures were prepared by vertical depositionmethod. The effects of particle size ratio and volume ratio on the structure ofbinary colloidal crystals were discussed. The formation and optical property ofbinary colloidal crystals were studied.Single-phase SiO₂, BaTiO₃and Fe₂O₃nano-particles were synthesized viaPechini sol-gel method. The structural coordination and thermal behavior ofas-prepared polymeric intermediates were investigated. The effects of pH valueand calcination temperature on the crystalline phase, morphology and particlesize of nano-particles were studied. Several binary metamaterial heterostructureswere prepared by self-assembly method with the obtained nano-powders. Thestructure of binary metamaterial heterostructures was discussed. The effects ofthe types and fabricating technique of nano-powders and filling process on thestructure of metamaterial heterostructures were studied. And the growth ofmetamaterial heterostructures was investigated.The results were listed:1) Uniform, monodisperse silica spheres, budded silica spheres andbinary silica spheres were successfully prepared by three St berprocesses. By comparing the morphology and particle size of silicaparticles obtained by three St ber processes with different reactantsconcentrations, the formation mechanism of colloidal silica sphereswas analysed.2) Monodispersed SiO₂colloidal spheres with about443⁷01nm wereprepared by St ber method when NaCl electrolyte was introducedinto the system. At the same [TEOS] and [NH₃], the NaCl modifiedSiO₂colloidal spheres are larger than unmodified SiO₂colloidalspheres. And the Zeta potential of the modified SiO₂spheres isimproved. When VNH3=3.5mL, Zeta potential of the modified SiO₂spheres is averagely heightened12.34mV. Hexagonal array colloidalcrystals were prepared by vertical deposition method and dual substrates method. The NaCl modified SiO₂spheres couldself-assemble into more ordered structure compared to theunmodified SiO₂spheres. Besides hexagonal array structure, squarearray structure was also synthesized by electrophoresis-assistedself-assembly. And the obtained square array structure is the （111）direction of face-centered cubic structure.3) The LS₂, LS₄, LS₆and LSxbinary metamaterial structures weredesigned. The L/S （volume ratio） and space occupancy of colloidalspheres were calculated. LS₂, LS₄, LS₆, LS_x1and LSx2binarymetamaterial structures were successfully prepared by verticaldeposition method. The structure of binary metamaterials is decidedby particle size ratio and volume ratio of colloidal spheres. Thegrowth mechanism of binary metamaterial structures was proposed.The optical properties of binary metamaterial structures wereresearched. The results show that the photonic band gap of365/70nm（80:1） binary metamaterial structure is in accordance with thetheoretical prediction of LS2non-close-packed binary structure.However, the photonic band gap of365/70nm （10:1） binarymetamaterial structure is different from the theoretical prediction ofLSxbinary structure.4) The nano-powders which could be used to prepare the metamaterialheterostructures were synthesized by Pechini sol-gel method. Theobtained SiO₂powders are amorphous particles with about10nm or20nm. The obtained BaTiO₃powders are cubic phase particles whichare found to be20³0nm globe-like particles、40⁶0nm globe-likeparticles or20¹30nm globe-like particles and blocks. The Fe₂O₃powders are pure α-Fe₂O₃phase. And the globe-like particles,coral-like blocks and porous blocks can be obtained. The particle sizeof small particles is about28⁶0nm.5) Several binary metamaterial heterostructures were successfullysynthesized with the nano-powders prepared by Pechini sol-gelmethod. The results show that the budded structure is obtained withSiO₂nano-particles. Two binary metamaterial heterostructures can be prepared with BaTiO₃powders. One includes LS₂, LS₄and LS₆strucrure, and another one includes the BaTiO₃particles which fillinto the voids of colloidal spheres between the layers. The urchin-likemetamaterial heterostructure is obtained with Fe₂O₃nano-powders.