Ideal dimers comprising gold nanoparticles with a smooth surface and high sphericity are synthesized by a substrate-based assembly strategy with efficient cetyltrimethylammonium bromide removal. An unprecedented structural and plasmonic uniformity at the single-particle level is observed since inhomogeneities resulting from variations in gap morphology are eliminated. Single ideal dimers are analyzed by polarization-resolved dark-field scattering spectroscopy. Contributions from transverse as well as quadrupolar and octupolar longitudinal plasmon coupling modes can be discriminated because of their orthogonal polarization behavior. The assignment of these higher order coupling modes is supported by computer simulations.

In article number https://doi.org/10.1002/smll.201702754, Sebastian Schlücker and co‐workers synthesize ideal gold dimers of two spherical gold nanoparticles with a controlled gap distance and gap morphology. While theoreticians have been able to describe the properties of such a model system, experimentalists have failed to synthesize it. Here, elastic scattering of an ideal gold dimer using white light together with an electron microscopy image is shown. The polar plot summarizes the polarization behavior of various higher order plasmon coupling modes.