| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 99 === 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.
|
|---|
