A Study on Colloidal Opal Grown by Dip-Coating Method

Photonic crystal is a dielectric material with periodic structure. We can control light propagation by utilizing photonic band gap which has connection with periodic structure. It can be used to fabricate novel optoelectronic devices. People are interested in this field either theory or application.his thesis is to grow colloidal opal by dip-coating method with monodispersed SiO2 ethanol suspension under various concentration and pulling velocity. The opal possess FCC structure under SEM. When constant concentration, increasing pulling velocity, the opal cross-section profile transfers from a smooth band to periodic growth bands. Also the opal thickness decreases. There exist an optimal concentration to grow a smooth and thickest opal while constant pulling velocity. Periodic growth bands are macroscopic defects. The microscopic defects are parallel striations, grains and point defects. The growth mechanism and how defects formed had been discussed in this thesis.he reflectance spectrum measurements showed consistent results between Bragg reflection and reflection peak position, which verified the opal possess FCC structure. The inverse FWHM of reflection peak is positively correlated to opal thickness. The Fabry-Perot fringes in reflectance spectrum also related to layers of opal. Using transfer matrix to fit the reflectance spectrum, we have got consistent results either peak position or Fabry-Perot fringes.