Fig. 2.

Optical properties of polyhedral nanoparticle dimers. (A) Illustrations of the four types of nanoparticle dimers examined, with red planes indicating the interparticle gap. Experimental dark-field spectra (B) and FDTD simulations (C) of the corresponding nanoparticle dimers. (D) 3D charge density maps show the highly polarized, multipolar nature of the interparticle gap at both laser excitation wavelengths in the SERS experiments. (E) The total electric field intensity calculated by integrating over all points within the plane of the interparticle gaps for each nanoparticle dimer. The solid vertical lines indicate the laser excitation wavelengths, and dotted lines indicate the 1,079 cm⁻¹ (1) and 1,590 cm⁻¹ (2) Stokes modes of 4-AMT.