奈米Epsilon鏡像結構陣列之表面電漿特性應用於表面增強紅外光譜

Abstract

當光照射到小於波長的金屬奈米粒子時，光與金屬上的電子形成侷域表面電漿共振的現象，光會被侷限在金屬奈米粒子表面形成強烈的電場分布。藉由這些強烈的電場分布，金屬奈米粒子可以應用在生物、化學分子的偵測，和粒子的光學捕獲等應用。 此外，侷域表面電漿的特性可藉由改變金屬奈米粒子的幾何結構來調變。在本片論文中，我們藉由實驗及模擬討論了金奈米Epsilon鏡像結構的參數改變對光學特性的影響，包括:外徑、內徑、棒狀結構的間距與寬度。我們觀察到要在對稱模態下產生最佳的電場分布，需要適當的內外徑尺寸與盡量小的棒狀結構的間距與寬度。在此條件下，金屬環的部分可提供電荷至兩個棒狀結構的尖端，透過窄小的間距相互影響形成強烈的電場分布。在所有參數中，我們發現縮小棒狀結構的間距最能有效地提升電場強度。因此，我們更進一步地將兩個金奈米Epsilon鏡像結構互相靠近，形成一個額外的窄小間距，在其中也產生強烈的電場分布。最後，我們在實驗中利用此結構增強PMMA分子的紅外光譜，展現了金奈米Epsilon鏡像二聚物結構於表面增強紅外光譜應用的潛力。

When light illuminates metal nano particle smaller than its wavelength, it couples to the electrons and induces local surface plasmon resonance (LSPR). A strong field distribution is then confined on the metal surface which can be applicate in bio or chemical molecule sensing and plasmonic trapping. Moreover, the LSPR characteristics of metal nano particle highly depends on its geometry. Therefore, in thesis, we investigated the optical properties of Mirror-Image Nanoepsilon (MINE) in experiment and simulation, by changing parameters, including outer and inner radii, rod width and gap size. We figured out that in symmetric mode, under proper ring width with thin rod width and small gap size, charge is supported from the ring part and gathers to the rod tips. The charge coupling through the small gap size, forms a strong and localized near field distribution in the center of the structure. Among, all the parameters, we found out that decreasing gap size is the best way to enhance strong field. Thus, we put two MINE together as a dimer with a small gap size, creating another hot spot. In the end, we did the experiment of surface enhanced infrared spectroscopy (SEIRS) on PMMA molecule by MINE dimer. We expect that gold MINE dimer structure can serve as a high sensitivity SEIRS device in the future.