Towards a complete photonic band gap in the visible

Abstract

The first part of the thesis describes the fabrication and the characterization of face-centered-cubic (fcc) photonic crystals (PCs) of dielectric (core-shell) spheres in a low-dielectric host (air). We demonstrate the synthesis and optical characterization of the PC's building blocks: well-defined core-shell colloidal particles and hollow shells of zinc sulfide (ZnS) and silica (SiO2). The synthesis method allows for the production of monodisperse particles with a tunable core-to-shell size ratio and total radius. By use of the controlled drying method, we demonstrate the fabrication of large planar PCs of well-defined thickness from SiO2, ZnS, and ZnS-core-SiO2-shell colloidal particles. We demonstrate, both experimentally and theoretically, that the relative stop gap width in the (111) fcc crystallographic direction in the case of high-index core and low-index shell spheres is larger than in a PC of homogeneous spheres of either material. The second part of the thesis focuses on the preparation and characterization of photonic materials of different degree of order made of metal colloidal particles. We demonstrate the synthesis and characterization of large (R > 100 nm) silver (Ag) particles. The particles are obtained by reducing silver nitrate with ascorbic acid in aqueous solutions in the presence of a protective polymer. The resulting particles are spherical porous aggregates with a low polydispersity (< 20%) and surface roughness on the order of a few nanometers. The optical properties on a single-particle level are well described if an effective dielectric constant is used. Depending on the volume fraction and the effective polydispersity, in water these particles form charge-stabilized glasses or crystals. Under illumination with white light, these samples display bright colors. A strong modulation is found in the reflectivity of photonic glasses possessing a short-range order only. The general features in the experimental spectra are found in the theoretical reflectivity spectra for fcc crystals. From our results, it is likely that amorphous metallo-dielectric materials can be used in some applications where the spontaneous emission of light needs to be modified. The last part of the thesis deals with PCs with complex lattices and PCs made of non-spherical colloidal particles. We present the fabrication of binary colloidal crystals through a simple layer-by-layer drying process. We demonstrate the fabrication of crystals with a stoichiometry of large (L) and small (S) particles of LS2 and LS. In addition, we observed the formation of a new LS3 binary crystal. By using spheres with different composition, one component can be selectively removed. As an example, we demonstrate the synthesis of a hexagonal non-close-packed colloidal crystal. We demonstrate the fabrication of PCs of ellipsoidal colloidal particles. By use of MeV ion irradiation, we deformed spheres into oblate ellipsoids as organized in a thin 3D colloidal crystal. Both the unit cell symmetry and the particle form factor have been changed as a result of the collective deformation process, leading to an appreciable tunability in the optical properties of the PC. Crystals,