金奈米雙環結構之間隙效應於侷域表面電漿耦合之影響與感測應用

Abstract

侷域表面電漿子模態會被電磁波激發於金屬奈米結構中。當這些奈米結構相互靠近時，侷域表面電漿子模態會產生強烈耦合，使得電場被集中增強在這些奈米結構的間隙內。在本篇論文中，我們展示了一個金奈米雙環的結構設計，並深入探討其隨著改變不同間隙大小的光學特性變化。相較於一般的奈米顆粒成對結構，奈米雙環具有更多且更強電場分佈的侷域電漿子模態，所以更加適合應用於感測上。 首先，我們利用有限元素法模擬奈米雙圓盤和奈米雙環的消光光譜，並分析各模態的電場分佈。接著藉由一連串奈米製程技術製作出擁有不同間隙大小的實際元件。在這些奈米雙圓盤以及雙環裡，由於侷域表面電漿子耦合的現象，我們都觀察到共振模態在縱向的偏振下隨著間隙大小變小會紅移，間隙內電場強度也會跟著被增強。不僅如此，奈米雙環的電場較強，而其模擬出的感測能力在10 nm的間隙下更能達到 1076 nm/RIU，而奈米雙圓盤只有901 nm/RIU。實驗上我們得到奈米雙環的高感測度在47 nm的間隙下能達到663 nm/RIU，比奈米雙圓盤在28 nm的間隙下的感測度531 nm/RIU要來的好。我們確信這樣的結構對於奈米感測更具發展潛力，如蛋白質，DNA或是一些有毒化學分子的偵測應用。

Localized surface plasmon mode could be induced by electromagnetic wave in metal nanostructures. When these nanostructures come in close, LSPR modes are strong coupling, leading to the electric field concentrated and enhanced in the gap of the nanostructures. In this thesis, we demonstrate a gold nanoring dimer structure design and well investigated the corresponding optical properties with varying gap sizes. Compare to typical nanoparticle dimer, nanoring dimer with more and stronger electric field distributions of LSPR bonding mode leads to better sensing applications. At first, the extinction spectra and related LSPR mode profiles of nanodisk and nanoring dimers with varying gap size are simulated and characterized by finite element method. And real devices with different gap sizes are fabricated by series of nano-fabrication process. We observed a red shift of LSPR modes and the enhanced electric field in the gap with decreasing gap size in longitudinal polarization for both nanodisk and nanoring dimers due to LSPR mode coupling. Moreover, the electric field intensity is stronger in nanoring dimer of which the sensitivity reaches to 1076 nm/RIU with gap size of 10 nm in simulation, while the sensitivity is only 901 nm/RIU for nanodisk dimer. In our experiment, high sensitivity of 663 nm/RIU for nanodisk dimer with gap size of 47 nm is obtained, which is better than the sensitivity of 531 nm/RIU for nanodisk dimer with gap size of 28 nm. We promise that it has more potential in nanosening such as protein, DNA, or toxic chemical molecule detections.