FAÇONNAGE DE MODES PLASMONS DANS DES COLLOÏDES D’OR

Abstract : The main objective of this thesis is to interpret experimental measurements of the plasmonic properties of gold colloidal particles. First, we study the optical near-field distribution around nano-platelets thanks to the photomigration technique. This indirect photo-chemical mapping uncovers a size effect by shining at 457 nm and 514 nm particles of different sizes, suggesting a quasi-modal response from the surface plasmons supported by these structures. This peculiar response is evidenced in the case of colloidal triangles of 500 nm side length. Then, we show that Two Photon Luminescence (TPL) offers another original way to probe the electromagnetic field distribution inside Au particles. We focus the TPL study on gold nano-rods and platelets. TPL maps show a strong confinement of the electromagnetic field inside these objects. Signal localization can be controlled by adjusting incident polarization. Simultaneously, we have developed a new tool based on the Green Dyadic Method (GDM) to reproduce and analyze TPL maps. They confirm specific near-field localization in the metal and provide a new insight into wavelength and particle shape influence. Our model suggests that TPL gives also access to the local density of plasmonic states in the particle and consequently that the coupling between two gold platelets could lead to a new design of a plasmonic modal logic gate. Finally, we have investigated the optical properties of gold nanoparticle chains. These nanoparticles fuse under the electron beam of the TEM. The fusion shifts plasmons resonances of the chains towards the infrared region. These plasmonic modes have been studied spatially and spectrally using Electron Energy Loss Spectroscopy (EELS). We have developed a theoretical model showing the link between the energy loss of a swift electron and the local density of states. Using the GDM, we have computed EELS maps of these nanoparticle chains.
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Alexandre Teulle. FAÇONNAGE DE MODES PLASMONS DANS DES COLLOÏDES D’OR. Physique [physics]. Université Toulouse 3 Paul Sabatier (UT3 Paul Sabatier), 2013. Français. ⟨tel-01792951⟩

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