電漿子奈米結構及紋理結構矽基板之製作於表面增強拉曼散射之應用

Abstract

本研究旨在討論奈米金屬誘發表面電漿效應與紋理矽基板之複合結構於表面增強拉曼散射之應用。本論文分為二個主題。第一部分利用理論及實驗手法討論懸架式奈米環金屬結構與奈米管矽基板複合基板之表面電漿效應。透過有限時域分析法模擬不同內外徑比值的尺寸對於局域性表面共振行為，並利用電子束微影製程及反應性離子蝕刻技術製作，再以暗場顯微散射光譜及表面增強拉曼散射光譜測量其光學性質及近場增強效應，與模擬結果相互印證。模擬結果顯示，偶極及四偶極模態在內外徑比值上升過程中被激發，其可被表面電場增強分布及電荷密度分析其混層理論解釋。實驗方面，藉由調整內外徑比值可有效調整其暗場顏色影像，顯示其應用於顏色顯示器之潛力；於拉曼光譜測量，實驗結果與模擬結果顯示良好之相依性，其驗證了表面電漿模態的演變，亦提供了拉曼光譜分子檢測之最佳指導方針。 本論文第二部分，利用水熱法成長銀奈米粒子/氧化鋅奈米線異質結構於奈米管矽基板，有效提升光光能捕獲及增加表面積，並利用異質接面引起之載子傳遞進一步提升表面增強拉曼散射，其增強機制可由異質結構能帶圖解釋。除此之外，利用紫外光誘發氧化鋅奈米線光觸媒效應，便可有效地降解待測分子，提供此表面增強拉曼基板重複利用之可能性。

The system consisting of metallic nanostructure and textured silicon substrate with enhanced light harvesting and strong electromagnetic field enhancements was studied in the present work. The thesis is divided into two topics. In the first topic, the effects of plasmonic behavior on a composite system consisting of suspended gold nanoring and silicon nanotube substrate were studied both theoretically and experimentally. The dependence of plasmonic behaviors on outer/inner diameter ratio (D/d ratio) of the gold nanoring and silicon nanotube was systematically studied using finite-difference time-domain method. On the other hand, the composite systems with different D/d ratios were fabricated using electron beam lithography followed by reactive ion etching and studied by both dark-field microscopy as well as Raman microscopy. In addition to the dipole-like resonance modes, the quadrupole-like resonance mode was also excited with the increasing D/d ratio, and both electric field profile and resonant surface charge distribution were studied to characterize the resonance configuration and to clarify the coupling phenomenon. Experimentally, by tailoring the D/d ratio, the dark-field image showed tunable colors and the potential for the color display application. Raman spectra were also obtained and showed good agreement with simulated enhancement factor which, in turn, provided the evidence of the evolution of resonance modes. This work provides the concept and guideline for designing the system consisting of metallic nanostructures and textured substrates for surface-enhanced Raman scattering application. In the second topic, the ZnO nanowires were grown on silicon nanotube substrate through hydrothermal process and the Ag nanoparticles were loaded on the ZnO branched nanowires. With the help of ZnO nanowires, the light harvesting effect could be enhanced and the surface area could be increased. Also, additional electric field enhancements would be induced due to the charge transfer between the heterojunction, which could further enhance the Raman signals. The mechanism behind the additional enhancements was elucidated by the band structure of the heterojunction. In addition, the photocatalyst properties of Ag/ZnO heterostructure were exploited to reuse the substrate through the degradation of probed molecules upon UV-irradiation.