Finite-Size Effects and Surface-Enhanced Raman Scattering from Molecules Adsorbed on Noble-Metal Nanoparticles
V.N. Pustovit, K.M. Walker and T.V. Shahbazyan
Jackson State University, US
Keywords: nanoparticles, sers, single-molecule spectroscopy
We study theoretically the role of strong electron confinement on surface-enhanced Raman scattering (SERS) from molecules adsorbed on metal nanoparticles. We describe a novel enhancement mechanism, relevant for nanometer-sized noble-metal particles, which originates from different effect that confining potential has on sp-band and d-band electrons. Namely, the spillout of delocalized sp-electrons beyond the classical nanoparticle boundary results in an incomplete embedding of sp-electron distribution in the background of localized d-electrons whose density profile follows more closely the classical shape. We show that a reduction of d-electron screening in the surface layer leads to the enhancement of the surface plasmon local field acting on a molecule located in a close proximity to metal surface. This results in the additional enhancement of the Raman signal which becomes more pronounced for small nanoparticles due to the larger ratio of surface layer to overall nanoparticle size. Our numerical calculations of Raman enhancement factor, performed using two-region model, indicate a significant increase of SERS as compared to previous electromagnetic model calculations.
Nanotech 2004 Conference Technical Program Abstract