Thesis presented October 16, 2018

Abstract :
Colloidal nanocrystals have important potential applications in different technological fields such as solar cells and thermoelectricity, thanks to their reduced fabrication costs and exotic and unique properties. In this thesis, a variety of advanced transmission electron microscopy (TEM) techniques is used to unravel the morphology, crystal structure and chemical composition of state-of-the-art Cu₂ZnSnS₄ (CZTS) and CsPbBr₃ and CuFeS₂ colloidal nanocrystals.
Firstly, the difficulties of these TEM observations and the found solutions are presented.
Then the details of the various TEM observations, such as Energy Dispersion X-ray (EDX) spectroscopy, High Resolution Transmission Electron Microscopy (HR-TEM), High Resolution Scanning TEM(HR-STEM) and Nanobeam Precession Electron Diffraction (NPED) are exposed and compared to synchrotron Small-Angle X-ray Scattering (SAXS) and Wide-Angle X-ray Scattering (WAXS) experiments.
For CZTS, different samples extracted at different times of the fabrication have been observed and a growth mechanism is proposed. For CsPbBr₃, the focus was put on the determination of the exact structure, cubic or orthorhombic, of the nano-crystals. For CuFeS₂, the influence of synthesis methods on the morphology and crystal structure are presented in an appendix.

Keywords:
TEM, nanocrystal, colloidal nanocrystals, Perovskite, Core/shell, Czts, Nanoparticles, Stem.

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