Plasmonique hybride : propriétés optiques de nanostructures Au-TMD, couplage plasmon-exciton

Abstract : Transition metal dichalcogenide materials (TMDs) are increasingly gaining attention, due to their unique optical, spintronic, and electronic properties. These properties result from the ultimate confinement in 2D monolayers of a direct band-gap semiconductor and the lack of inversion symmetry in the crystallographic structure. To control and enhance the optical response of these materials, it is interesting to integrate them with plasmonic nano-resonators. The TMDs/plasmonic hybrid systems have been extensively studied for plasmon-enhanced optical signals, photocatalysis, photodetectors, and solar cells. In this context, this thesis deals with the interaction between TMD monolayers and gold nanostructures. In a first part, an hybrid system composed of CVD grown MoSe2 monolayers transferred on gold nanodisks was studied. Surface plasmon resonance was tuned by controlling the nanodisks size and the inter-disks separation. The optical properties of the nanostructures are probed by means of spatially resolved optical transmission and photoluminescence spectroscopies. Fano-type coupling regime between the surface plasmon of the gold nanodisks and the MoSe2 exciton was evidenced by a quantitative analysis of the optical extinction spectra based on an analytical model. Our interpretations were supported by numerical simulations. The number of MoSe2 monolayer dependence as well as the Temperature dependence of the plasmon-exciton interaction was investigated. Our results were quantatively analysed on the nanometric scale by studying the local electromagnetic near-field and the excitonic transition dipole momentum interaction. Furthermore, the Raman scattering of MoSe2@Au system was carried out. A particular situation was investigated where a resonant interaction between the surface plasmon of nanodisks and A exciton of v occur. The contribution of these two resonances leads to a resonant surface enhanced Raman scattering (SERRS) effect. The Raman Scattering excitation is selected to resonantly excite the Surface Plasmon resonance and MoSe2 excitonic transition simultaneously. The relative contribution of the surface Plasmon and the confined exciton to the resonant Raman scattering signal is pointed out. In this resonant condition, a hyperthermia effect was detected. Numerical simulations of the SERS gain were useful to figure out the main factors affecting the SERS intensity enhancement in MoSe2@Au. In a second part, the TMD monolayer was used as a substrate of Au nanoparticles. Au nanoislands were deposited on mono- and few-layered MoSe2 flakes. Photoluminescence (PL) measurements revealed a net quenching of the MoSe2 photoluminescence. To figure out the origin of this quenching three possibilities were discussed (i) the charge transfer between the TMD monolayer and the Au particles (ii) the direct to indirect gap transition of the TMD electronic band structure caused by the strain induced by the metal deposition (iii) structural disorder imparted by the nanoparticles in the TMD/metal interface. Owing to the Raman scattering measurements and using the radiative emission of the gold nanoparticles, we evidenced a charge transfetrt between the metallic nanostructures and the semiconductor. In order to complement our interpretations a comparative study with respect to optical properties of TMD covered by a silica film was carried out. The present work was held within the NeO group in CEMES, in a frame of a collaboration with the group of thr Pr. Jun Lou from Rice university, Houston.
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Ines Abid. Plasmonique hybride : propriétés optiques de nanostructures Au-TMD, couplage plasmon-exciton. Micro et nanotechnologies/Microélectronique. Université Paul Sabatier - Toulouse III, 2017. Français. ⟨NNT : 2017TOU30333⟩. ⟨tel-01996786⟩



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