Electromagnetic Theory of Tunable SERS Manipulated with Spherical Anisotropy in Coated Nanoparticles

We develop an electromagnetic theory of surface enhanced Raman scattering (SERS) from coated nanoparticles with spherical anisotropy in the quasistatic limit. The multipolar polarizability of the spherically coated nanoparticle is derived on the basis of the first-principles approach, and then we employ the Gersten-Nitzan model to investigate SERS from molecules adsorbed on the coated nanoparticles. It is found that the introduction of spherical anisotropy into the core or the shell provides a novel approach to tailor the surface plasmon resonant frequencies and enhanced SERS peaks. In addition, the dependence of the SERS spectra upon the size is addressed. Our investigation can be applied in prospective stimulated Raman scattering schemes in nano-optics and plasmonics when a certain extent of anisotropy is involved.