Thèses

Vendredi 4 Novembre 2022 à 14h00.

Opening-gap Plasmonic Antennas : A Surface Plasmon Polariton Source

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Directeur de thèse / thesis director : Julien LAVERDANT

Membres du jury / jury members :

Alexandre BOUHELIER
Alberto BRAMATI
Natalia DEL FATTI
Emmanuelle DELEPORTE
Julien LAVERDANT

Résumé / Abstract :

Nanopatch antennas based on metallic nanoparticles-on-mirror configuration offer great advantages as a potential source for launching surface plasmon polaritons (SPPs). In this work, we propose a plasmonic platform consisting of gold bipyramid nanoparticles (AuBPs) deposited over a gold thin film. A sub-10nm TiO2 gap is introduced between the two metallic structures to prevent conductive contact. The synthesized AuBPs have the ability to support a strong localized surface plasmon resonance along its longitudinal axis which behaves like a radiating dipole. When the nanoparticles are brought to interact with the gold mirror, each AuBP resembles a nanoscale nanopatch antenna with an “opening-mouth”, which allows for effectively launching SPPs over the metallic surface around the bipyramid. In the terms of the experiment, we employ a leakage radiation microscope working in the dark-field configuration to study the scattering of the antenna and also excite and collect the SPPs. Here, we highlight the importance of the orientation effect in the optical response of the AuBPs. A rich mode structure ranging from the visible to the near-infrared regime is opened by tilting AuBP with one tip touching the substrate, whereas other orientations only display a single dipolar longitudinal mode. The plasmon modes exhibit both radiative nature and are confined within the gap. The COMSOL calculation confirmed that the plasmon gap mode behaves similarly to the Fabry-P´erot resonances. Finally, the bipyramid nanopatch is employed to optically excite SPPs, showing that the efficiency of launching SPPs is resonantly enhanced at the plasmon resonance wavelength of the mode. Especially, in the comparison to the plasmon generated by scattering from a dielectric bead nanoparticle of silica on the same gold substrate, the bipyramid nanopatch induces a greater SPPs efficiency by around 1 order of magnitude. These characteristics of the AuBP nanopatch can pave the way for electrically driven plasmon antennas, for which many applications such as energy harvesting or quantum information, are beneficial.

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