Electromagnetic effects on a molecule at a metal surface : I. Effects of nonlocality and finite molecular size

Abstract

The electromagnetic effects on a molecule near a metal surface are considered with the view to understanding the surface-enhanced-Raman-scattering (SERS) effect. The image enhancement effect is calculated including the nonlocal response of the metal and finite molecular size. The effect is much reduced ( x 10-5) from that for a point molecule above a local metal but can still give a gain [approximate] 103. The power emitted by a dipole above a smooth surface is also calculated. For an Ag surface the power emitted in the form of photons, surface plasmons, and electron-hole excitations are found to be in the ratio 1 : 3 : 106. The numerical results are calculated using the semi-classical infinite-barrier model of the metal surface with a Lindhard dielectric function modified to take into account finite electron lifetime and core polarization.