| Popis: |
We developed novel understandings pertaining to the ordering and optical properties of crystalline colloidal array (CCA) materials and applied these understandings to develop novel non-close-packed inverted photonic crystal materials. CCA materials are highly charged electrostatically stabilized colloidal particles in water which readily form face centered cubic or body centered cubic lattice structures. Because their periodicity is on the order of the wavelength of light, CCA materials have the ability to Bragg diffract light in the UV, visible and NIR regions of the electromagnetic spectrum. We utilized time resolved normal incidence reflection spectroscopy to probe the degree and kinetics of CCA ordering during the CCA crystallization process. Bragg diffraction interference fringe intensity is used to qualitatively determine the overall CCA ordering between CCA samples which have incremental additions of added ionic impurity. We defined the physical mechanism for anomalous reflection peaks obtained in the specular reflection direction from photonic crystal materials. We utilize variable angle specular reflection spectroscopy to probe angular ranges about the normal to the (111) planes of an fcc CCA to monitor the dispersion of anomalous reflection peaks. We correlated these reflection peaks to the diffraction from higher order Miller index crystal planes through Braggs Law. We explain the origin of these peaks as the result of a multiple diffraction process whereby light is first Bragg diffracted into a beam from a set of higher order Miller index planes and consecutively diffracted by the in plane (111) periodicity into the (111) specular reflection direction. We also uncovered a novel use for CCA and PCCA materials allowing us to fabricate a non-close-packed inverted photonic crystal material. Our novel fabrication method consists of an infiltration and condensation of a sol-gel precursor into the hydrogel matrix of a PCCA and then the subsequent removal of the PCCA material. We show that the original high ordering of the CCA is maintained through and in-depth study which examining the (111) in-plane ordering. Tuning the CCA particle number density, prior to the fabrication process provides the ability to readily tune the Bragg diffracted wavelength of the final inverted photonic crystal. |
