Fabrication of colloidal photonic bandgap crystals and their applications

Abstract

In this thesis, colloidal photonic bandgap crystals with sub-micrometer sized colloidal particles as a building block were self-assembled through various routes and their applications were investigated. In chapter 2, fabrication methods of three-dimensional colloidal crystals are described. Firstly, colloidal crystals were fabricated by ice-crystallization. A water based polystyrene suspension was frozen to selectively crystallize water. The frozen water then extrudes polystyrene beads outward from the ice region. The concentration of the polystyrene beads increases rapidly and they are assembled together into a regular structure. The ordered structure showed iridescent color, typical coloring of the ordered colloidal crystal, and revealed photonic stop band. Rapid freezing tended to create various structures including spherical, bending, and planar structures, whereas slow freezing created better-ordered planar structure. Secondly, colloidal particles are assembled at water-air interface by fast evaporating water. The polystyrene colloidal particles protrude easily from the water surface by evaporating water and the protruding particles distort the water surface. The distorted surface causes the strong attractive capillary force between colloidal particles and thus colloidal particles assemble into ordered structure. The ordered structure then grows due to the convective transport of particles to the ordered region. The effective density of the ordered structure becomes lower than that of water and consequently the assembled particles floats on the water surface. Further evaporation of water makes the floating ordered colloidal particles to form three-dimensional structure by the repetition of above process. This method was also applied to assemble various sized-colloidal particles (240, 500, 900 nm in diameter, respectively). Thirdly, multiply layered colloidal crystals were fabricated by dipping method introducing external electric field. Mono-layered coll...