浸提法光子晶體生長及其機制研究

Abstract

光子晶體為一具有週期性結構之介電材料，改變晶體結構週期便能改變其光子能隙特性，從而控制光的傳播行為，可用於製作許多新型光電元件。故無論在光學理論及應用方面都引起人們很大興趣。 本論文旨在以浸提法生長光子晶體。使用粒徑均一(偏差值小於5%)之二氧化矽奈米粒子之酒精懸浮液，在不同濃度、拉速條件下生長光子晶體。在掃瞄式電子顯微鏡觀察下，晶體以面心立方結構組成。當固定濃度、拉速漸增時，晶體剖面輪廓由平滑轉為週期性帶狀結構，且晶體厚度(層數)漸減；而當拉速固定時，則存在一最佳濃度可長成平滑且最厚之晶體。晶體缺陷分為巨觀與微觀兩部分，週期性帶狀結構為巨觀缺陷，而微觀缺陷則有平行條紋、塊狀晶粒、點缺陷等。文中也討論了不同狀態下的生長機制及缺陷成因。 對這些晶體進行反射頻譜量測，其反射峰位置與布拉格反射理論值相符，再次驗證晶體為面心立方結構；且反射峰之半高寬倒數(1/FWHM)與晶體厚度呈正相關；反射頻譜中出現的Fabry-Perot震盪圖譜亦與晶體層數有關。針對反射頻譜以傳遞矩陣(transfer matrix)加以擬合，不論反射峰位置、Fabry-Perot震盪圖譜均得到一致性結果。

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. This 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. The 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.