Absolute extinction cross sections of individual silver nanocube dimers are measured using spatial modulation spectroscopy in correlation with their transmission electron microscopy images. For very small interparticle distances and an incident light polarized along the dimer axis, we give evidence for a clear splitting of the main dipolar surface plasmon resonance which is found to be essentially induced by cube edge rounding effects. Supported by discrete dipole approximation and finite element method calculations, this phenomenon highlights the high sensitivity of the plasmonic coupling to the exact shape of the effective capacitor formed by the facing surfaces of both particles, especially in the regime of very close proximity.

International audienceThe impact of quantum confinement on the width of the surface plasmon resonance of a metal nanoparticle is theoretically investigated in a model system formed by a silver nanosphere in different environments. Calculations are performed using the time-dependent local density approximation (TDLDA) for nanoparticle diameters up to about 11 nm, permitting precise quantification of the surface plasmon broadening due to size reduction. As expected, this is found to be inversely proportional to the particle diameter, but with an amplitude strongly depending on the environment (increasing by a factor of 4 when changing from vacuum to alumina). This is ascribed to the fact that damping is governed by the electronic surface spill-out (inherent in any quantum model) and thus strongly depends on the surface profile of the confining potential, that is, on the particle surface conditions