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In-situ microscopy in corrosive environment
Nedvěd, Matěj ; Velický, Matěj (referee) ; Kolíbal, Miroslav (advisor)
This diploma thesis focuses on in-situ electron microscopy and its application to monitoring the chemical reactions on the surfaces of nanomaterials. The possibilities offered by this technique are presented, and the existing solution of an in-situ scanning electron microscope used for experiments is described. The thesis introduces Janus two-dimensional materials based on transition metal dichalcogenides with a focus on their preparation. A detailed description follows regarding the preparation of thin layers of WSe2 material using mechanical exfoliation and experiments conducted using an in-situ microscope. These experiments involved annealing of WSe2 material in the presence of hydrogen sulfide (H2S) while simultaneously observing it with an electron microscope, aimed to facilitate the chalcogenide exchange in this material. The morphology, composition, and optical properties of the material were subsequently analyzed using Raman spectroscopy and photoelectron spectroscopy. Finally, an experiment resulting in the successful exchange of selenium in WSe2 for sulphur is presented.
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Preparation and characterization of nanomaterials for electrochemical energy storage
Bouša, Milan ; Kavan, Ladislav (advisor) ; Fejfar, Antonín (referee) ; Velický, Matěj (referee)
Graphene research is nowadays one of the worldwide most prominent fields of interest in material science due to many extraordinary properties of graphene and related materials. However, the different techniques of synthesis and subsequent handling and/or treatment have a substantial impact on the properties of the graphene and thus a lot of efforts have been focused on developing of the advanced methods for graphene preparation and characterization. Graphene can be easily produced by oxidation and consequent exfoliation of the bulk graphite; however, resulting graphene oxide needs to be reduced back to graphene-like structure due to partial restoration of sp2 network. Herein, a detailed study of the structural evolution of the graphene oxide during electrochemical treatment has been performed using X-ray photoelectron, Raman and infrared spectroscopies and the results were compared with non-oxidized graphene nano-platelets. Additionally, graphene oxide in composite with LiFePO4 olivine material, which is electrochemically almost inactive in a freshly made state, has been tested by repeated electrochemical cycling. Using various electrochemical methods, the progressive electrochemical activity enhancement has been observed and spontaneous graphene reduction was identified as responsible for this...
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