以有限時域差分法與高效率化介電函數研究核殼奈米結構的侷域性表面電漿模態

Study of Localized Plasmon Modes in Core-shell Nanostructures by using FDTD Method with an Efficient Dielectric Function

呂駿佑(Chun-Yu Lu)

指導教授 ： 張顏暉

國立臺灣大學/理學院/物理研究所/博士(2010年)

https://doi.org/10.6342/NTU.2010.02532

摘要

由於其侷域性表面電漿模態會與光有強烈交互作用，貴重金屬奈米顆粒之光學性質已成為一重要研究領域。 製程技術的進步使得我們能夠設計擁有多種形狀跟功能的核殼結構，像是奈米米、奈米環和奈米核殼,這些核殼結構由他們在光電、生物和電子設備上的應用吸引到很多注意。這份論文研究光與電介質核金屬殼奈米結構的交互作用，在論文內所使用的模擬的工具是圖形處理器單位化的有限時域差分法，圖形處理器可以加速我們模擬的效率並且減少模擬時間。 此外，一個新且有效率的介電函數模型被併入在我們有限時域差分法中，此模擬結果可以準確地描述金跟銀的色散在波長180奈米到2000奈米之間，於是我們使用此有限時域差分法研究電介質/金屬核殼圓柱對的侷域性表面電漿模態。
首先，我們先著重一對電介質/金屬核殼奈米圓柱的侷域性電漿模態。 模擬的結果發現避雷針作用跟混成電漿模態是兩個造成強烈電場分佈的重要因素，同時我們也利用相位延遲效應來激發無偶極矩的電漿模態。 除了模擬電場分佈跟消散光譜外，我們也研究能量流與電漿模態偶合的關係，結果發現與電漿模態有關的光學奇異點可以被發現在一對核殼奈米圓柱中的，光旋渦與鞍點可以在光與這圓柱對作用的同相對稱偶極矩模之能量流中發現，其中光漩渦的轉動方向可以藉由變化兩圓柱間的寬度以及介質核的光學常數來控制。 最後，我們延伸對於電介質/金屬核殼圓柱對的討論從一對到三對，研究結果顯示電介質/金屬核殼圓柱對可以同時作為表面增強拉曼散射和表面增強紅外吸收光譜的選擇。

關鍵字

有限差分 ； 奈米光電 ； 表面電漿

並列摘要

Noble metal nanoparticles (NPs) are well-known to exhibit a strong interaction with light due to the excitation of localized surface plasmons. Recent advances in nanofabrication have enabled us to design the nanostructures with different shapes and functionalities, such as nanorices, nanorings, and nanoshells. These core-shell nanostructures have attracted much attention due to their applications in opto-electric, biological, and electronic devices. This dissertation reports the studies of the interactions between the light and dielectric-core metallic-shell nanostructures. The simulation tool used in this dissertation is Graphic-Process-Unit-Based (GPU-Based) finite-difference time-domain (FDTD) method. The GPU is graphic processor unit that can greatly speed up our simulation efficiency and reduce simulation time. In addition, a new and efficient dielectric function model was developed and incorporated into our FDTD, and the simulation result can describe accurately the dispersion of gold and silver in the wavelength range between 180nm and 2000nm. This FDTD tool was then used to study the localized plasmon modes in dielectric-core gold-shell nanocylinders.
First, we focus on the plasmon modes of a core-shell nanocylinder pair. The simulations results show the lightning-rod effect and hybridized plasmons are two important factors in enhancing the electric field. We also studied the excitation of non-dipolar plasmon modes by using the phase retardation effect. In addition to simulating the extinction spectra and electric field distributions, the relation of energy flows and localized plasmon modes is also studied. Optical singularities associated with plasmon modes are found to exist in a core-shell nanocylinder pair. The optical vortices as well as saddle points can be observed in the energy flow pattern of light interacting with the core-shell nanocylinder pair in its in-phase symmetric dipolar plasmon mode. The rotating direction of the optical vortices can be tuned by varying the width of the gap between the nanocylinder pair and the value of the permittivity of the dielectric core. Finally, we extend our studies on core-shell nanocylinder pairs from one pair to three pairs. The results show the core-shell nanostructures have a property that makes it an ideal candidate for both surface enhanced Raman scattering (SERS) and surface enhanced infrared absorption spectroscopes (SEIRA).

並列關鍵字

FDTD ； nanooptics ； plasmonics

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