| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 102 === The surface enhanced fluorescence (SEF) of silver island (SI) film was studied theoretically in this thesis. Since the silver islands possess the surface plasmon resonance (SPR), the local electric field can be enhanced to raise the excitation rate on the nearby molecules. Additionally, the apparent quantum yield of SI on the emitting molecules is high. Therefore, the overall enhancement factor of SI on SEF is increased. However, this SEF very depends on the molecular relative location and orientation, the excitation wavelength and emission wavelength. We modeled the SI as an oblate silver spheroid. Our aim is to find the optimal conditions for SEF.
First, we studied the performance of an oblate spheroid irradiated by a -incident plane wave. At a specific excitation wavelength and a fixed distance from SI, the location to obtain the maximum electric field is estimated. After that, the orientation corresponding to the excitation rate is determined. Additionally, the apparent quantum yield at this location and orientation is calculated. Subsequently, the enhancement factor is obtained. We also discussed the results of different incident angles, different distances, and different sizes (e.g. aspect ratio). Numerical results show that the location of the strongest field is always near the edge of SI. The optical molecular orientation direction is almost normal to the surface of SI. Moreover, the SPR of SI is red-shifted as the aspect ratio increases. Using this property, the enhancement factor of SI on a specific molecule can be tailored. In particular, the enhancement factor of SI on FITC-molecule is quantitatively studied.
Basically, we solved the Maxwell’s equations by using the multiple multipole (MMP) method. Since the boundary conditions at some proper collocation points on the boundary need to satisfy, a system of equations are constructed in terms of several unknown coefficients, representing the intensities of these higher-order poles. Through the singular value decomposition (SVD), these unknown coefficients are obtained. Using these coefficients, the EM fields in the exterior and interior fields can be calculated. Consequently, the excitation rate, apparent quantum yield and enhancement factor can be obtained.
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