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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]

Abstract: The size effects on SrTiO3 nanoparticles have been investigated by means of Raman spectroscopy with changing the grain size in the range 10–80 nm. The intensities of the first-order polar TO2 and TO4 modes increase as the grain size reduces, suggesting the enhanced interaction of the surface-defect dipoles on the grain boundary. By contrast, the intensities for the first-order nonpolar TO3 mode decrease with reducing the grain size. Further we have found that the Raman frequencies of the vibration modes are very sensitive to the variation of the grain size. The softening of the TO2 and TO3 modes with decreasing the grain size indicates the increase of the Ti–O bond length, which is consistent with the lattice expansion investigated by XRD. We have ascribed the size effects to the negative pressure effects due to the enhanced interaction of the surface-defect dipoles. [Copyright &y& Elsevier]