Templated Fabrication Of Photonic Crystal Structures And Their Optical Properties

Photonic crystal (PhC) has attracted many interests from researchers both experimentally and theoretically since the proposal of its concept by E. Yablonovitch in year1987. Due to the existence of photonic band gap (PBG) in photonic crystals, it can control the propagation of light inside solids, and thus leads to many unique optical phenomena such as superprism, negative refraction, etc., which make the material of potential application in many fields such as optical information processing and communication. There have been many fabrication methods for photonic crystals such as X-ray exposure method, laser interference method, etc. However, these methods are of high cost and low efficiency, and thus less feasible for most laboratories. Thus, the self-assembly method for colloidal crystals has attracted many attentions due to its high efficiency, low cost and good final product quality. At the same time, bio-templating has also attracted many researchers because their unique structures designed by nature. Theoretically, there have also been many new findings in photonic crystals, however, there is still a long way to go to combine them with experimental results, which is essential for the realization of their final applications. Base on these facts, this dissertation focus on both theoretical analysis and experimental fabrication and characterization of the photonic crystals. The works in this dissertation include:1. The self-assembly of polystyrene microspheres has been demonstrated due to its low cost and high efficiency. The relationship between fabrication conditions, such as suspension density, growing temperature, with the final template quality and formation of different types of structures has been studied. The reason for the formation of defects in the colloidal crystals has also been studied. The photonic band gaps of the prepared templates were measured by the reflectance spectra.2. The prepared colloidal crystal template was used to fabricate α-Fe2O3/Si two-dimensional photonic crystal slab, and its morphology and reflectivity were characterized. Due to the difference in the refractive indices of the two kinds of materials and the diffraction pattern observed under different incident light wavelengths, we infer that the behavior of the photonic crystal slab can be the same as an ideal two-dimensional photonic crystal. Through detailed theoretical calculation and experiments, we found that the diffraction pattern of the photonic crystal was different from that of an ordinary diffractive material. The diffraction pattern will only appear under certain incident wavelengths and photonic crystal lattice constant, moreover, the light spots on the screen show elliptical shapes rather than round ones. These results may be helpful in the development of beam-splitters or displaying devices.3. The photonic amorphous diamond structure in the feather barb of Rosy-faced Lovebird has been studied. The structural color caused by the unique structure has been demonstrated. These barbs were used as templates to fabricate ZnO photonic amorphous diamond structure through a solution-dipping method followed by high-temperature calcination. The reflectance spectra show that the photonic band gap of the prepared structures will not shift with the incident angle, which is different from ordinary photonic crystals. The center of the photonic band gap is at around500nm, which falls inside the visible emission range of the ZnO material. Photoluminescence measurement shows that the emission intensity of the visible range of the ZnO material was suppressed. Moreover, due to the existence of the photonic band gap, the emission intensity of the ultraviolet range was enhanced, thus leads to an increase in the UV/visible peak intensity ratio. This suppression and enhancement effect is stable and will not shift with the incident or observation angle, which may be very important for the realization of ZnO UV laser emitter.4. The photonic crystal properties of the porous structures in the butterfly Papilio Paris have also been studied. Using the photonic structures as template, the ZnO replicas of these structures have been obtained. In the reflectance measurement, it was found that such structures will have interactions with visible light, especially around wavelength of530nm, which shows as a decrease in reflectivity. This will suppress the visible emission intensity of ZnO material as well as enhance the UV emission intensity, and thus leads to the improvement of the UV emission properties of the ZnO material. This proves that the photonic structures in the butterfly wing scales can also be utilized to modify the emission properties of the semiconductor materials, which is meaningful to the realization of UV emitters based on ZnO materials.