| Summary: | 碩士 === 逢甲大學 === 材料科學所 === 96 === Photonic crystals are periodic optical nanostructures that are designed to induce the interference of photons in a way that periodicity of a semiconductor crystal or a dielectric and the air gaps affects the motion of electrons or electromagnetic waves. Thus the artificial photonic band-gap (PBG) can be associated with photonic crystals. Sol-gel process becomes a popular method to fabricate the massive quantity of uniformly sized oxide microspheres.
The goals of this study are consisted of the following aspects: (a) the sol-gel synthesis of monodispersed zinc oxide (ZnO) microspheres, and (b) the electrophoretic self-assembly (EPSA) mechanism of ZnO microspheres to construct the 3-D photonic crystals, and (c) the characterization of band gap and optical properties of 3-D closely packed, ordered zinc oxide photonic crystal templates. The EPSA process in this study was manifested as an effective method to assemble colloidal particles from either suspension or colloid onto the surface of various electrically conductive substrates. The EPSA process can easily produce a deposit of three-dimensionally ordered structure composed of microspheres on the surface of the electrode substrate for a very short time.
The results showed that the size of ZnO microspheres, which were successfully synthesized by the two-staged sol-gel process, was in the range of 100~450 nm. The ZnO spheres were distributed in narrow particle size range and well-dispersed in the isopropyl alcohol (IPA) with acceptable surface potential. The ZnO photonic crystal with the face-centered closely packed (fcc) structure can be easily formed by electrophoretic self-assembly (EPSA) technique. There was a slight difference between theoretic and measured peak value of reflectivity data for such photonic crystals made of ZnO (300 nm size). We proposed that the voids existing within the ZnO primary particles due to the surface roughness of packed ZnO spheres would be in conjunction with a decrease of the observed refractive index and dielectric constant of ZnO photonic crystals. Thus the reflectivity curves of ZnO photonic crystals contained widened peaks and the blue-shift behavior. In the future, we cam employ the EPSA technique to prepare numerous templates for fabrication of designed photonic crystals.
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