NC-AFM studies on CeO2 film and CeO2 crystal surfaces

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Titel: NC-AFM studies on CeO2 film and CeO2 crystal surfaces
Autor(en): Olbrich, Reinhard
Erstgutachter: Prof. Dr. Michael Reichling
Zweitgutachter: Dr. Clemens Barth
Zusammenfassung: Cerium oxide has become an outstanding material in catalytic applications over the last decades. In this thesis, the morphology and atomic structure of thick cerium oxide films and ceria single crystals is investigated by non-contact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM). The ceria films are prepared by annealing cycles from room temperature up to 1100K in ultra high vacuum (UHV) and in an oxygen atmosphere. The films exhibit large smooth terraces separated predominantly by O-Ce-O triple layer height step edges but in contrast to the ceria single crystals some inhomogeneities are observed on the terraces. By annealing the film at 1020K to 1070K in UHV several intermediate phases can be stabilized ranging from the fully oxidized phase CeO2 to the fully reduced phase Ce2O3. These phases have a unique stoichiometry with regular arranged vacancies in the surface and subsurface as revealed by density functional theory (DFT) calculations. The film can be reoxidized by annealing in an oxygen atmosphere as shown by X-ray spectroscopy (XPS). The annealing in oxygen atmosphere also results in a surface with less inhomogeneities. This makes the ceria films an excellent model system for catalytic applications. Further in this thesis a measurement series exhibiting absorbed water on the film surface is presented and discussed. Also line defects observed on the film and on the single crystal are analyzed.
Schlagworte: ceria; NC-AFM; CeO2; KPFM; non-contact atomic force microscopy; surface reconstructions
Erscheinungsdatum: 30-Mai-2018
Enthalten in den Sammlungen:FB04 - E-Dissertationen

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