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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]

Abstract: The amplitudes of the dipole and quadrupole modes for gold nanoshells have been investigated with various dielectric constants for the core and the embedding medium and with various size of the nanoshells by means of Mie theory. With the increase in the dielectric constant of the core, it is found that the strengths of dipole and quadrupole modes become weak. We also observe with the increasing dielectric constant of the embedding medium that the strength of the quadrupole mode is enhanced quickly, whereas that of dipole mode increases first and then decreases. We further find that the amplitude maximum of the dipole mode appears when the total radius of the nanoshell reaches to 50 nm even if the ratio of the inner and outer shell radii is fixed. We have ascribed the changes of the dipole and quadrupole modes to the competition among the variations of induced surface charges, conduction electrons and oscillation electrons. [Copyright &y& Elsevier]