調控奈米間隙界面與模擬超穎材料表面電漿子共振於增強拉曼散射光譜之應用

Manipulating of Nanogap Interfaces and Simulation on Metamaterials Surface Plasmon Resonance on the Application of Surface-Enhanced Raman Spectroscopy

林詩哲(Shih-Che Lin)

指導教授 ： 薛承輝

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.10512

摘要

表面電漿子是金屬表面電子和入射光共振的現象，依種類可分為傳播於金屬表面的表面電漿子 (Surface plasmon polaritons, SPP)與集中在局部的局部表面電漿子(Localized surface plasmon polaritons, LSP)，使用經過設計的奈米級微結構，即可以在結構的特定位置上激發出局部表面電漿子，用來增強局部區域的電場。然而，表面電漿子只會和特定波長的入射光發生共振，共振波長則決定於奈米微結構的材質、間距和幾何形狀，最常使用的共振金屬材質為金、銀和鋁，假如兩個奈米微結構的金屬中間存在一奈米間隙時，局部表面電漿子會在間隙做強烈的共振，於間隙表面生成數百到千倍的電場，本論文即在探討不同的奈米間隙距離和不同的金奈米微結構幾何，對共振波長與電場增強倍數的影響。首先是探討有奈米間隙的兩顆金奈米橢球，其共振波長隨橢球長寬比和不同奈米間隙距離的關係，使用的方法為時域有限差分法（Finite-Difference Time-Domain, FDTD）數值模擬計算，以及利用米式散射理論（Mie scattering theory）和電偶極理論(Electric dipole theory)，推倒出共振波長的解析解，最後再和美國橡樹嶺國家實驗室(Oak Ridge National Laboratory, ORNL)製作出的懸架式金奈米橢圓微結構，量測出的增強拉曼散射光譜實驗結果做比對與分析。第二部份是探討金奈米指南針的超穎材料，金奈米指南針的超穎材料，藉由中間指針和周圍環的奈米間隙產生共振，其利用環型幾何形狀和針型幾何形狀，所支持的兩種不同共振模態，來形成可支援兩種共振波長的增強拉曼散射微結構，同時因為兩種模態所產生的電荷分佈不同，金奈米指南針的微結構同時也是電磁誘導穿透(Electromagnetically Induced Transparency, EIT)的超穎材料，本論文將使用時域有限差分法數值模擬來做探討，並嘗試使用電子束微影(E-beam lithography)、電子束蒸鍍(E-beam Evaporator)等技術來製作出金奈米指南針微結構。

關鍵字

奈米光學天線 ； 電子束微影 ； 時域有限差分法模擬 ； 表面增強拉曼散射光譜

並列摘要

Surface plasmon is a resonance phenomenon between incident light and surface electrons of metal which can be classified as two types, surface plasmon polaritons (SPP), propagating at metal surface, and localized surface plasmon (LSP), concentrating at local region. By using designed nanostructure, localized surface plasmon can be induced at specific location on the structure surface enhancing electrical field at local region. However, surface plasmon only resonant with particular wavelength, and the resonance wavelength is decided by the materials, gap distance and geometry of nanostructure. The common materials for surface plasmon usage is gold, silver and alumina. If there is a nanogap between two metal nanostructure, localized surface plasmon will resonant strongly at the nanogap inducing hundreds or thousands times of local electric field. This thesis is to study the different nanogap distance and nanostructure geometry on the impact of electric field enhancement factor. First part is to investigate the resonance wavelength of two ellipsoid gold particles with a nanogap. The relation of resonance wavelength to the different aspect ratios of gold ellipsoid particles and gap distance is also studied. The Finite-Difference Time-Domain (FDTD) simulation method is used as research approach and the analytical solution of resonance wavelength is also derivate by Lorentz-Mie theory and Electric dipole theory. Finally, the simulated and analytical result is compared with the experimental measured SERS signal of free-standing gold ellipse nanoantenna fabricated by Oak Ridge National Laboratory (ORNL). The second part is to investigate the gold nano compass metamaterials. The gold nano compass metamaterials use the nanogap between needle and surrounded ring to resonant. This structure could support two resonant mode for SERS application, one is determined by needle geometry with another determined by ring geometry. Meanwhile, the gold nano compass metamaterials is also a electromagnetically induced transparency (EIT) metamaterials due to the different charge distribution of two resonance mode. This thesis will use FDTD simulation method to investigate and try to fabricate the gold nano compass structure by using E-beam lithography and E-beam Evaporator technic.

並列關鍵字

Optical nanoantenna ； Electron beam lithography ； FDTD simulation ； SERS ； Lorentz-Mie theory

參考文獻

[1] A. Sommerfeld, "Ueber die Fortpflanzung elektrodynamischer Wellen langs eines Drahtes", Annalen der Physik 1899, 303(2), pp. 233-290.

[2] J. Zenneck, "Uber die Fortpflanzung ebener elektromagnetischer Wellen langs einer ebenen Leiterflache und ihre Beziehung zur drahtlosen Telegraphie", Annalen der Physik 1907, 328(10), pp. 846-866.

[3] R. W. Wood, "On a Remarkable Case of Uneven Distribution of Light in a Diffraction Grating Spectrum", Proceedings of the Physical Society of London 1902, 18(1), pp. 269.

[4] U. Fano, "The Theory of Anomalous Diffraction Gratings and of Quasi-Stationary Waves on Metallic Surfaces (Sommerfeld?s Waves)", J. Opt. Soc. Am. 1941, 31(3), pp. 213-222.

[5] E. Kretschmann and H. Raether, "Radiative decay of non radiative surface plasmons excited by light", Z. Naturforsch. 1968, (23A), pp. 2135-2136.