金奈米桿及偏心球殼結構之光學特性研究

Optical Properties of Gold Nanorods and Nonconcentric Nanoshells

蔡孝彥(Hsiao-Yen Tsai)

指導教授 ： 郭茂坤

國立臺灣大學/工學院/應用力學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.01548

摘要

本研究探討三維金桿、核殼金桿及偏心金球殼等結構與光波及螢光分子交互作用下所產生的各種現象。以Maxwell電磁理論作為基礎，並使用多重多極展開法做為計算方法，探討上述金奈米粒子，在入射平面電磁波的激發下所表現的表面電漿子共振特性，並考慮不同入射方向的平均效應。此外以一電偶極波源模擬螢光分子，分析奈米粒子與螢光分子之間的耦合作用所產生之螢光增益效果。
分析結果顯示半徑越大且細長比越為大的金奈米桿具有較長的長軸共振波長，並能提供較強的吸收及散射截面積。若以矽殼包覆金奈米桿則更能使長軸共振波長紅位移。在螢光增益研究中，發現螢光分子之位置及其振盪方向對螢光增益的影響甚高，當其位於金桿兩端並沿長軸方向振盪時會得到最佳的螢光增益，且當金桿尺寸較大時，愈能提升整體的螢光增益效應。雙顆金奈米桿結構中，對稱性的排列可造成較長波長和較高效率的bonding mode共振，反之，當金桿結構的對稱性下降，則會出現另一antibonding mode之短波長低效率的共振。
而偏心金球殼在入射光以表面電漿子共振波長照射下，在金殼較薄處之近場能產生較大的電場增強，當雙顆偏心金球殼以較薄殼處相對時，則在兩球殼間隙之電場亦會因彼此耦合而更加增強。

關鍵字

奈米桿 ； 矽殼 ； 偏心殼核 ； 表面電漿子共振 ； 多重多極展開法 ； 螢光分子 ； 平均吸收截面積 ； 平均散射截面積 ； 量子效率 ； 螢光增益 ； 長軸表面電漿子共振

並列摘要

In this thesis, we studied the interactions among fluorescent molecules, visible light and gold nanorods (GNRs) or silica-coated gold nanorods, nonconcentric gold nanoshell (GNSs). Based on Maxwell's equations, the multiple-multipole (MMP) method was used to solve these problems. We studied the surface plasmon resonances (SPRs) of these nanoparticles irradiated by different incident plane waves with different polarizations. In additionally, the average effect was studied by considering all possible incident directions. Moreover, the electric dipole was used to simulate a fluorescent molecule for analyzing the plasmonic enhancement on fluorescence resulting from the coupling between these nanoparticles and the molecules.
The results indicate that the longitudinal SPR of GNR of larger aspect ratio and larger radius is more red-shifted, and the absorption and scattering cross sections become larger. The longitudinal SPR of silica-coated GNR is red-shifted from that of bare GNR. In addition, the enhancement factor of GNR on fluorescence is sensitive to the location and the orientation of molecule. When the molecule is placed at the end-cups of GNRs and oscillates along the long axis, a larger enhancement factor is obtained. A larger GNR can improve the enhancement factor. For the GNR dimer, the symmetry of this structure can induce a bonding-mode resonance at a longer wavelength. On the contrary, as the symmetry of GNR dimer is reduced, the antibonding-mode resonance of a shorter wavelength is induced.
The nonconcetric GNSs produces an enhanced electric field at the thinnest gold shell region. Hence, the electric field in the gap of a dimer can be enhanced, if the thinner gold shells of dimer are close to each other.

並列關鍵字

gold nanorods ； silica-coated gold nanorods ； nonconcentric gold nanoshell ； surface plasmon resonance (SPR) ； multiple-multipole (MMP) ； fluorescent molecule ； average absorption cross section ； average scattering cross section ； quantum yield ； fluorescence enhancement ； longitudinal SPR

參考文獻

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