- 學位論文
單顆和雙顆多層奈米粒子之表面電漿子模態分析與對螢光分子的螢光增益之研究
Plasmon Modes of Multi-layered Nanoparticles & Dimer and Their Surface Enhanced Fluorescence
摘要
本研究單顆金和銀奈米殼球的平均螢光增益，matryoshka奈米粒子自身plasmonic Fano resonance現象及其各種螢光增益，最後探討雙顆銀奈米殻球各種表面電漿子共振模態(SPR)與螢光增益。根據Maxwell電磁理論作為基礎，利用Mie理論與並矢格林函數，整理單顆球型奈米粒子受平面波與電偶極波源的電磁場解析解，除此之外，並使用多重多極展開法做為計算方法，處理雙顆散射體的電磁場。最後定義激發效率、量子效率、螢光增益以及考慮螢光分子隨機分佈、任意極化方向的平均螢光增益。 螢光增益與螢光分子位置、震盪方向、入射平面波極化方向、電漿共振模態彼此有密切的關係。考慮一般實驗螢光分子均勻分布、極化方向難以控制的情況，以平均螢光增益(AEF)的概念來解釋各種散射體的光學特性較為恰當。另外，再加入史托克位移(Stokes shift)效應，討論單顆與雙顆多層奈米球對螢光增益的影響。 matryoshka奈米粒子此結構內核黃金與外殼黃金發生內外不對稱結構電漿子模態耦合現象，在近場吸收頻譜中會有局部峰值，而稱為plasmonic Fano resonance，此兩不對稱結構彼此發生了牽引交互作用，造成金屬內耗吸收的能量增強，而在遠場會有Fano dip產生，且內外耦合會混雜出多種電漿子共振模態，bonding mode與anti-bonding mode，然而若如果改變結構尺寸，使得耦合增強，那麼Fano factor (q)的絕對值會上升。最後一部份雙顆銀奈米殼球，若將他們靠越近也會有耦合(bonding)現象，但不是Fano resonance，此外此結構就像一個奈米天線一樣，容易激發出雙顆長軸共振dipole mode。
關鍵字
Mie理論 ； 並矢格林函數 ； 表面電漿子共振 ； 多重多極展開法 ； 雙顆奈米殼散射體 ； matryoshka奈米粒子 ； Fano resonance ； Fano dip ； Fano factor ； 螢光分子 ； 激發效率 ； 量子效率 ； 平均螢光增益 ； Stokes shift ； bonding與anti-bonding mode並列摘要
In this thesis, we discuss the surface plasmonic modes and interactions among fluorescent molecules, visible light and gold nanoshells (GNSs) or silver nanoshells (SNSs), the nanomatryoshka partical (Au-SiO2-Au), the silver nanoshell dimer. Based on Maxwell's equations, analytical solutions of the field excited by a plane wave and the electric dipole source out of the multi-layer spherical structure result from Mie theory and dyadic Green’s functions respectively. The multiple-multipole (MMP) method was used to solve fields of the dimer case. In addition, we also define the excitation rate, quantum yield, enhancement factor (EF) and average enhancement factor (AEF). The enhancement factor (EF) has very much to do with the plasmonic modes, the arbitrary orientation, the location of molecules and the polarization of the incident wave. The concept of AEF can avoid overestimating or underestimating fluorescent intensity because it is hard to control the location and orientation of molecules in experiment. Furthermore, with Stokes shift effect, we observe the difference of AEF between three kinds of nanoparticles: nanoshells, nanomatryoshka and the nanoshell dimer. For the structure of nanomatryoshka, plasmon modes of the inner Au core and the outer Au shell hybridize two different modes, forming a lower energy narrow bonding mode and a higher energy broad anti-bonding mode. The modes of two asymmetry structures couple each other and induce a plasmonic Fano resonance and Fano dip, which appearing on the peak of the absorption spectra and the local minimum of the scattering spectra respectively due to the destructive interference of the two modes. However, if we change the dimension of nanomatryoshka to enhence the coupling of the two modes, the absolute value of Fano factor (q) will increase. Finally, for Ag nanoshell dimer, if we decrease their gap, they would couple each other (bonding) rather than Fano resonance. Furthermore, the nanoshell dimer is like a nanoantenna and easily excited longitudinal dipole mode.