Advanced transmission electron microscopy studies of semiconductor nanocrystals synthesized by colloidal methods

Fabio Agnese 1
1 LEMMA - Laboratoire d'Etude des Matériaux par Microscopie Avancée
MEM - Modélisation et Exploration des Matériaux : DRF/INAC/MEM
Abstract : The investigations of semiconductor nanocrystals (NCs) led to fascinating scientific results in optoelectronic devices. In order to fulfill certain requirements, i.e. cheaper costs, higher efficiencies, environmental friendly components etc., new methods are explored in solution-processing, band gap and energy level engineering. Particularly, the method of synthesis can alter the optoelectronic properties. Therefore, a better understanding of the intricate factors during synthesis will lead to improved performances. Advanced electron microscopy provides a precise way to gather information about morphology, crystal structure and chemical composition of materials with a spatial resolution down to the atomic level. The first part of this thesis deals with the optimization of the synthesis and sample preparation for high resolution transmission electron microscopy (HRTEM).The second part deals with the growth mechanism of Cu2ZnSnS4 NCs synthesized by a colloidal method. The morphology and stoichiometry of the samples extracted after different time intervals are characterized by HRTEM and electron dispersion spectroscopy (EDS). Two complementary methods, Nanobeam Precession Electron Diffraction (NPED) and High Resolution Scanning Transmission Electron Microscopy by High Angle Annular Dark-Field Imaging (HRSTEM-HAADF), provide an in-depth crystal structure characterization.Moreover, the crystal structure of CsPbBr3 NCs is solved by probing STEM-HAADF simulations. This approach is able to differentiate cubic and orthorhombic crystal structures, which is otherwise impossible by diffraction techniques. Finally, the influence of synthesis methods on the morphology and crystal structure of CuFeS2 NCs is investigated by HRTEM for thermoelectric applications.
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Fabio Agnese. Advanced transmission electron microscopy studies of semiconductor nanocrystals synthesized by colloidal methods. Material chemistry. Université Grenoble Alpes, 2018. English. ⟨NNT : 2018GREAY043⟩. ⟨tel-02012615⟩

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