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The influences of the symmetry-breaking on the plasmon resonance couplings in the isolated gold nanotube and the gold nanotube dimer have been investigated by means of the finite element method. It is found that the core offset of gold nanotubes leads to the red-shifts of the low energy modes and the enhanced near-field on the thin shell side of the symmetry-broken gold nanotube (SBGNT). In the weak coupling model of the SBGNT dimer, the interference of the bonding octupole mode of the dimer with the dipole modes causes a strong Fano-like resonance in scattering spectrum. The Fano dip shows a red-shift and becomes deep with the increase of the offset-value. In the strong coupling model of the SBGNT dimer, the coupling between two SBGNTs induces giant electric field enhancement at the gap of the dimer, which is much larger than that in the symmetry gold nanotube dimer. The SBGNT with larger offset-value exhibits stronger near-field at the "hot spot".

The influences of the anisotropic permittivity and permeability in inner core on the Fano resonance have been investigated in Ag nanoshell by means of Mie scattering theory. The decreased inner core radius can enhance the coupling between superradiant and subradiant dipole modes and hence a distinct Fano profile. With increasing the tangential permittivity or permeability of inner core, the Fano resonance shows a redshift and the magnitude of Fano profile increases. The variation of Fano resonance with anisotropic permeability of the core is much weaker than that induced by anisotropic permittivity. We further find that the combined action of the increased tangential permittivity and permeability of inner core can induce a significant enhancement of Fano resonance in Ag nanoshell., (© 2012 American Institute of Physics)

The extinction spectra of a three-layered metal nanoshell, which consists of a particle with a dielectric core, a middle Ag (Au) layer, and an outer Au (Ag) shell, have been investigated by means of the Mie theory. With a decrease in the outer shell thickness or the middle layer thickness, the wavelengths of the localized surface plasmon resonance (LSPR) for SiO2–Ag–Au (SiO2–Au–Ag) nanoshells show distinct redshifts and the full widths at half maximum (FWHMs) for the dipole peaks in the extinction spectra decrease first and then increase. We have further investigated the influence of the embedding medium on the LSPRs for SiO2–Ag–Au and SiO2–Au–Ag nanoshells and found that the resonance wavelengths of the particles show redshift and the FWHM of the dipole peak increases with increasing the dielectric constant of the embedding medium. The calculated results indicate that the LSPR of the three-layered gold-silver nanoshells can be controlled to the near-infrared region by changing the geometry, which has practical biomedical application. [ABSTRACT FROM AUTHOR]

The plasmon-exciton couplings in Ag-CuCl-coated nanowires (ACNWs) have been investigated by using the scattering theory and the finite element method. It is found with increasing the shell thickness that the dipole plasmon resonance of the Ag nanowire can be tuned through the exciton resonance in the CuCl shell. The strong coupling between the plasmon resonance in the Ag nanowire and the exciton resonance in the CuCl shell leads to two new hybridized plexcitonic modes. The dispersion curves of the plexcitonic modes in the ACNWs are studied, and the obtained splitting energy is about 88 meV. We further find that the destructive interference between the plasmon and exciton resonances results in the plasmon-exciton induced transparency. As the TE wave propagates through the ACNW array, an extraordinary transmittance can be found in the ACNW array at the scattering dip of the ACNW. [ABSTRACT FROM AUTHOR]

The influence of the spherical anisotropy (SA) of a middle layer on the plasmon resonance couplings in the sandwiched gold nanoshell (Au/SA/Au) has been investigated by means of a modified Mie theory. It is found that the plasmon couplings in the Au/SA/Au nanoshells are more sensitive to the permittivity along the radial direction of SA layer than the permittivity along the tangential direction. With increasing the anisotropic value of the middle layer, the dipole peaks of antisymmetric ω mode and symmetric ω mode both show blue-shifts, while the shift of the antisymmetric ω mode is larger than that for the symmetric ω mode. The larger anisotropic value of the SA layer induces the stronger near-field outside the nanoparticles for the antisymmetric ω mode, while the smaller anisotropic value makes the larger near-field for the symmetric ω mode. We further have found that the middle SA layer with smaller anisotropic value is helpful to obtain larger electric fields inside the nanoshells, which may be useful for their potential applications in nonlinear optics. [ABSTRACT FROM AUTHOR]

Abstract: The electric field enhancements in Au/Ag and Ag/Au core/shell nanoparticles have been investigated by means of quasi-static theory. The maximum enhancements of outside fields for Au/Ag and Ag/Au nanoshells occur along the incident polarization at plasmon resonance wavelength. It is surprised that the largest field enhancement in the shell of Ag/Au nanoshell occurs along the polarization direction, while that for Au/Ag nanoshell is perpendicular to the incident polarization. At off-resonance wavelength 1000 nm, the general shape of the field pattern is similar to that in resonance case except for much weaker amplitude. Furthermore, for the seamless nanoshells, the maximum enhancements of the electric field increase by increasing the shell thickness. As the shell thickness is small, the hot spots play an important role in the enhancement of the local electric field. [Copyright &y& Elsevier]

The weak peak at ultraviolet region observed by Zhu and Zhang in gold nanoshells should not be ascribed to the coupling of the “quadruple resonance,” which may be interpreted in terms of the contributions of the interband transitions in the Au layer. In addition, the quasistatic theory used by Zhu and Zhang is not suitable for investigation of the optical properties of gold nanoshells when the total radius of the shell is larger than the quasistatic limit. Furthermore, it is obvious that the strength and position of the local field factor peak should vary with the radial distance and the polar angle. [ABSTRACT FROM AUTHOR]