Preparation And Properties Of Anti - Opal - Structured Photonic Crystal Materials

Since Yablonovich theoretically showed the ability of three dimension periodic dielectric materials to possess a photonic band gap in 1987, photonic band gap materials have become an important and popular area of research. The strong interest in photonic band gap materials stems from their potential to confine and control the propagation of light with minimal losses. Inverse opal structure, as an important three dimensional periodic dielectric material, has great promising applications in optical communication, photonic computing, switching, lasing. photo catalysis, gas sensor, etc.In this doctorate dissertation, the opal films were successfully prepared with vertical self-assembly method. The opal films made of different diameter PS microspheres show different colors. The PS microsphere of the opal films arrange as well-ordered hexagonal close-packed structure on top view, and face-centered cubic structure on cross section. The testing values of the band gap positions of the opal films are consistent with the calculating values, and can be described with Bragg’s law. The band gap positions of the opal films can be modulated by changing the distance between the neighbouring (111) planes or the angle of incident light.Inverse opal tin dioxide (SnO;) films were fabricated with sol-gel method cooperative opal template. The perfect inverese opal structure was formed. The inner structure of SnO2 inverse opal films show inverse opal hollow spheres built up with SnO2 nanocrystals. The research of optical property shows that, for the opal films, the experimental reflectance spectra confirmed the wavelength maximums of the reflectance light λmax are consistent with the theoretical values. The SnO2 precursor might not completely fill the void of opal films that causes the experimental λmax deviating theoretical λmax so much. Compared with the experimental reflectance λmax of the opal films. the corresponding experimental reflectance λmax of SnO2 inverse opal films shift left.Inverse opal cerium dioxide (CeO2) films were prepared with polystyrene (PS) microsphere opal template and sol-gel method, and characterized in detail. The opal template and inverse opal CeO; show different colors in the light of halogen tungsten lamp and have a long-range ordered three dimensional periodic structure. Comparing with the opal template, the size of the inverse opal CeO2 shows shrinkage. The randomly selected positions of opal and inverse opal almost have the same peak position. The true filling factor of CeO2 is different from the theoretical value and calculated by testing the reflecting peak. The inverse opal CeO2 can modulate light by changing the diameter of air sphere and have directional stop band gap in the visible spectrum, which is expected to be some advanced and promising applications.Inverse opal titanium (TiO2) films were prepared with opal templates and sol-gel method. The inverse opal TiO2 films show different colors in the light of halogen tungsten lamp, and have well-ordered three dimensional periodic macropore and mesopore which originate from the opal templates. Since the influence of TiO2 precursor permeation and calcination, the filling factor f cannot be tested, but can be calculated according to the the testing values of band gap positions of inverse opal TiO2. The inverse opal TiO2 films can modulate light by changing the diameter of air sphere and have directional stop band gap in the visible spectrum.The SnO>2 inverse opal was prepared with a simplified opal cooperating with sol-gel method. The simplified method could spare much work and avoid the operation of the SnO2 inverse opal scraped from microslide. There are many macropores and mesopores in the SnO2 iverse opal. The superior performance of the SnO2 inverse opal sensor to methanol gas was also carefully investigated. In contrast to the reference gas sensors, the response of the SnO2 inverse opal sensor increases several folds and reaches as high as ～95 for 500 ppm methanol gas detection, the detection limit is as low as 1 ppm in practice. This work also shows that this special ordered cavity structure endow the semiconductor oxides possessing excellent sensing performances toward dilute gas detection, and they could become a very promising novel family for gas sensing in the future.