Plasmonic Modes Analysis of Metallic Nanoshells
Date Issued
2011
Date
2011
Author(s)
Jiang, Chong-Yu
Abstract
The plasmonic modes of Au and Ag nanoparticles (NPs) and nanoshells (NSs) excited by plane waves and electric dipoles are studied by using Mie theory and dyadic Green’s functions; e.g. the dipole, quadrupole and sextupole modes. For the plane wave excitation, the absorption and scattering cross sections are analyzed. For the dipole excitation, the near-field and far-field responses (e.g. radiative and nonradiative powers) are analyzed. Furthermore, to study the enhanced FRET between a donor and acceptor by these modes, two types (symmetric and anti-symmetric) of bi-dipole are used for simulation.
Numerical results show that anti-symmetric bi-dipole can excite the dipole and sextupole modes, and the symmetric one the quadrupole and octupole modes. These modes are in agreement with those excited by a plane wave. For Au NP and NS, only the dipole and quadrupole modes are observed, while the other higher-order modes are not. In addition, there is a strong absorption band at 510-540 nm. For the Ag NS, the dipole, quadrupole, sextupole, and octupole modes are observed. Moreover, these modes are red-shifted as the ratio of the core radius to the shell thickness increases. In addition, the strong absorption band is at 330-355 nm. The quadrupole mode exhibits its superiority in the near and far fields. Therefore it can be utilized to form a resonant cavity for enhancing the FRET of a donor and acceptor. This is to say the quadrupole mode of Ag NS can be used to realize the spaser-based nanolaser.
Finally, the plasmonic modes of Ag/Au alloy NS are studied. These modes are in between those of Ag NS and Au NS, depending on the ratio of alloy.
Subjects
nanoshell
dyadic Green’s functions
absorption cross section
scattering cross section
radiative power
nonradiative power
symmetrical bi-dipole
anti-symmetrical bi-dipole
dipole mode
quadrupole mode
Forster resonance energy transfer (FRET).
Type
thesis
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