Plasmon Modes of Multi-layered Nanoparticles & Dimer and Their Surface Enhanced Fluorescence

• Main Authors: Huang-Chih Chen, 陳皇志
• Other Authors: Mao-Kuen Kuo
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/58780885189664535337

碩士 === 國立臺灣大學 === 應用力學研究所 === 101 === 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.