Optical Properties of Gold Nanorods and Nonconcentric Nanoshells
Date Issued
2011
Date
2011
Author(s)
Tsai, Hsiao-Yen
Abstract
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.
Subjects
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
Type
thesis
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