Plasmon dispersion in self-organized Au nanoparticle arrays

We report on the dispersion relations of surface plasmon resonance (SPR) modes in spatially extended self-organized two-dimensional arrays of closely spaced gold nanoparticles (NPs). The arrays are supported on uniaxially rippled LiF substrates that trigger the organization of the metallic gold NPs in sequences of closely spaced chains. We measured the dispersion of the longitudinal and transverse SPR modes of these chains and successfully reproduced the experimental data by means of a modified effective-medium model. The calculations show that the interchain electromagnetic coupling increases by almost one order of magnitude the SP group velocity in well-defined regions of the Brillouin zone with respect to isolated chains.