Directed Assembly of Hybrid Colloids for Optics

This thesis is dedicated to finding a new route towards the realization of optical metasurfaces using “bottom-up” approaches based on wet chemistry and self-assembly.In this project, we use an emulsion-based formulation route to synthesize clusters of gold nanoparticles. The formulation route involves emulsifying a suspension of gold nanoparticles in water into an oil phase using adapted surfactants. This step is followed by the controlled evaporation of the water from the droplets under low pressure to confine the nanoparticles in the final clusters. The surface of the gold nanoparticles were previously functionalized in order to retain their surface plasmon resonance properties in the final assembly. The structure of the clusters, precisely their internal gold volume fraction f, is controlled by varying the molar mass and surface density of the grafting polymer. The final structure of the clusters isstudied using small angle x-ray scattering (SAXS), transmission electron microscopy (TEM) and cryogenic transmission electron microscopy (cryo-TEM).The optical scattering properties of the synthesized clusters are studied using a variable angle polarization resolved static light scattering (SLS) setup. The data measured using this setup are analyzed and also compared to theoretical calculations and simulations. The influence of the size R and the volume fraction f of the clusters on their scattering properties is experimentally evidenced using the SLS setup. The presence of electric and magnetic multipoles and their contributions to the scattering properties are experimentally demonstrated. The experimental results are in good agreement with the simulations which indicate that clusters with radius R = 120 nm and volume fraction f higher than 0.3 exhibit exceptional directional scattering properties as expected for Huygens scatterers used for the fabrication of metasurfaces.