Surface-enhanced Raman scattering near small nanoparticles: a microscopic approach

Abstract

A microscopic model for surface-enhanced Raman scattering (SERS) from molecules adsorbed on small noblemetal nanoparticles is developed. In the absence of direct overlap of molecular orbitals and electronic states in the metal, the main enhancement source is the strong electric field of the surface plasmon resonance in a nanoparticle acting on a molecule near the surface. In small particles, the electromagnetic enhancement is strongly modified by quantum-size effects. It is shown that, in nanometer-sized particles, SERS magnitude is determined by a competition between several quantum-size effects such as the Landau damping of surface plasmon resonance and reduced screening near the nanoparticle surface. Using time-dependent local density approximation, the spatial distribution of local fields near the surface and enhancement factor for different nanoparticles sizes are calculated.