Figure 12.

(a) The dimer under investigation is formed by two gold nanoparticles with radius $a$ and separated by a gap $g$; the laser is polarized along the main axis. (b) Extinction coefficient for a single sphere and for the dimer (with different gaps) as a function of the wavelength. (c) Continuous lines: SERS enhancement (SERS EF in the figure) for a single sphere and for the dimer (with different gaps) as a function of the wavelength; the enhancement is calculated at the point where the surface of one of the two nanoparticles crosses the axis $Z$. Dashed line: SERS enhancement for the dimer with $g$ = 2 nm, averaged over the whole metallic surface. Reproduced with permission from Le Ru et al. [6]. Copyright (2009) Elsevier B.V.