Double effective medium model for the optical properties of self-assembled gold nanoparticle films cross-linked with alkane dithiols

We present a comprehensive and structurally correct optical model for layers of nanometer sized gold particles, cross-linked with alpha,omega-alkane dithiol molecules, HS-(CH2)(n)-SH with n = 2, 8, 15. The solution requires a two-stage, three-phase effective medium model based on the observed nanostructure of the three constituents, gold, thiol, and voids. Voids and their topology, which were neglected in previous models, prove to be crucial in the explanation of the optical properties.