The Surface Enhanced Raman Scattering From Coated Nanoparticles With Radial Anisotropy

Surface-enhanced Raman scattering (SERS) has attracted much attention since 1974 due to its wide potential applications. For instance, SERS plays an important role in the modern sensing such as molecular detection and nanoparticle-based biosensor. The metallic nanoshell has become a unique plasmonic system and has been studied intensively in various imaging and spectroscopic applications, by employing the high tunability in its plasmon resonance frequencies as well as the enhanced local fields in the vicinity of the nanoshell. In view of the fact that the enhancement of SERS can be realized by the choice of the core-shell structure and by the suitable adjustment of physical and geometric parameters of the core (or the shell), SERS from these nanoshell substrates has been studied systematically. It is of our interest to investigate the SERS for a molecule adsorbed on a metallic nanoparticle with spherical anisotropy in the quasistatic limit. Our thesis includes two parts:1. Electromagnetic theory of SERS based on a first-principles approachWe establish the formula of SERS enhancement ratio from coated nanoparticles with spherical anisotropy. We present a first-principles approach to show both the potential distributions and electric field distributions in the quasistatic limit at first. Then, we derive the mutilpolar moments and polarizability analytically. In the end, the dependence of SERS enhancement ratio on spherical anisotropy and geometrical parameters is given on the basis of Gersten-Nitzan model. 2. Tunable SERS manipulated with spherical anisotropy in coated nanoparticlesWe have investigated the SERS enhancement spectra from coated nanoparticles involving spherical anisotropy. Different types of core-shell structured nanospheres are studied. The interconnections between SERS enhancement ratio, anisotropy ratio, core-shell structure, resonant shifts, the orientation of the molecule and the size dependence are systematically studied. Numerical results show that the introduction of spherical anisotropy will provide an alternative promising way to achieve significant enhancement of SERS signal, and to adjust the surface plasmon resonant frequencies in a wide frequency region, exhibiting a tunable Raman scattering.