Effect of Nanoparticle Symmetry on Plasmonic Fields: Implications for Single-Molecule Raman Scattering

The strong electromagnetic field localization required for the observation of single-molecule surface-enhanced Raman scattering (SMSERS) is readily obtained when the studied molecule is adsorbed inside the gap between closely adjacent nanoparticles. The interactions of adsorbed molecules with the electric field of light are influenced by the nanoparticle arrangement. This chapter discusses a series of spectroscopic and theoretical studies to better understand the mechanisms behind such interactions. It presents a systematic summary of the plasmon mode picture of the smallest nanoparticle clusters that are relevant to the discussion: dimers and trimers of spherical silver nanoparticles. The chapter shows how the shape of the plasmon spectrum of a cluster can be correlated with the shape of the Raman spectrum of an adsorbed molecule. It examines the relation between the polarization of the Raman-scattered light and the plasmon mode structure of the cluster.