ED Sciences Chimiques
Synthesis of silicon spheres for optical metamaterials
by Megan PARKER (ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux)
The defense will take place at 10h00 - Amphithéâtre Institut de Chimie de la Matière Condensée de Bordeaux 87 Avenue du Dr Albert Schweitzer, 33600 Pessac
in front of the jury composed of
- Glenna DRISKO - Directrice de recherche - CNRS - Directeur de these
- Patrick ROSA - Chargé de recherche - CNRS - CoDirecteur de these
- Laurence CROGUENNEC - Directrice de recherche - CNRS - Examinateur
- Eric HILL - Directeur de recherche - University of Hamburg - Examinateur
- Chloé THIEULEUX - Directrice de recherche - CNRS - Rapporteur
- Karine PHILIPPOT - Directrice de recherche - CNRS - Rapporteur
Light-matter interactions can be harnessed and exploited through precise material design choices, leading to the design of novel optical components. Silicon particles have become promising candidates in the design of optical metamaterials. Thanks to their high refractive index with low adsorption coefficient at visible frequencies, Si particles exhibit intense light scattering in the visible light spectrum. The scattering is a result of Mie resonances, an optical phenomenon which describes the interaction between light and sub-wavelength dielectric particles. The ideal Si particles for scattering in the visible should be spherical, between 75 and 200 nm, monodisperse, dense and crystalline. Larger particles are interesting candidates for optical applications in the infrared. Solution-phase syntheses of silicon particles, which may permit higher output and better control over size and form, have been historically limited to producing small Si particles (< 20 nm in diameter). In the course of this thesis, dual Si precursor systems in solution are explored to offer better control over the size and shape of Si particles. In the first approach, a silicon Zintl phase is combined with a hexacoordinated Si coordination complex, bis(N,N′-diisopropylbutylamidinato) dichlorosilane. The choice in solvent and precursor ratio greatly affects the size of Si particles attainable. In toluene and using an excess of Si coordination complex, particle sizes can be controlled from 45 to 230 nm in diameter, greatly extending the limits of current solution phase syntheses. The amidinate ligand is found to impact particle size. The refractive index of a single particle is measured and found to be near that of bulk Si, ensuring that the particles will exhibit intense light scattering. This approach is then adapted to other redox systems where a silicon Zintl phase can also be combined with a silicon halide (providing the Si (IV) species) and surfactants to produce an even larger range of Si particle sizes (up to 400 nm in diameter). In the final section of this thesis the bis(N,N′-diisopropylbutylamidinato)dichlorosilane complex was decomposed alongside a cylochexasilane in supercritical conditions (460°C, 345 bar). The particles were then self-assembled into a monolayer via an ethanol/butanol suspension on an air-water interface and particle-particle interactions were studied. Sharp resonances are observed in the effective thin film, which are important in the design of high quality factor optical metasurfaces. The development of this fully bottom-up approach toward a monolayer of spheres, along with the simultaneous development of solution syntheses toward Si spheres at ambient conditions, will offer new avenues toward developing large scale Si-based metasurfaces.