Optical response of individual nano-objects on an absorbing substrate.

Etienne Pertreux, Anna Lombardi, Mike Hettich, Paolo Maioli, Aurélien Crut, Fabrice Vallée and Natalia Del Fatti (team FemtoNanoOptics),with colleagues from Strasbourg and Bordeaux, have published an article entitled «Surface plasmon resonance of an individual nano-object on an absorbing substrate: quantitative effects of distance and 3D orientation» in the journal Advanced Optical Materials.

The optical response of metal nano-objects largely differs from that of bulk metals due to the appearance of strong resonances (surface plasmon resonances). In this size range, optical properties strongly depend on the local environment of the nano-object: resonances are thus in particular affected by its deposition on a substrate. To understand the origin of this effect and characterize it, the authors have compared the optical responses of individual elongated nano-objects (rod and bipyramid) deposited on dielectric and absorbing substrates. These experiments have demonstrated a spectral broadening of resonances on absorbing substrates, with variable amplitude. The comparison of spectroscopy experiments with numerical simulations has revealed the key-parameter controlling this effect, namely the penetration in the substrate of the intense electromagnetic fields generated near nano-object tips, which depends on the substrate/nano-object distance and on the 3D orientation of the latter. This geometrical characterization could be independently performed using electron tomography, confirming the origin of the demonstrated effect.

02/02/2016