@phdthesis{Zoellner2014, author = {Z{\"o}llner, Marvin Hartwig}, title = {Microelectronics meets catalysis: An interdisciplinary approach on the structure-property relationship of single crystalline Ce1-xPrxO2-δ films on Si(111)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-30687}, school = {BTU Cottbus - Senftenberg}, year = {2014}, abstract = {Motivation: Ceria attracted a lot of attention for microelectronics (e.g. high-k gate oxide, buffer layer for heteroepitaxy) and catalysis (e.g. selectiveoxidative and dehydrogenating reactions), due to its inherent structural (similar crystal structures and small lattice mismatch with respect to silicon) and electronic (Ce4+/Ce3+ valence state variation and formation of oxygen vacancies) properties. Thus, single crystalline epitaxial ceria thin films are well investigated. Although, the neighbouring rare earth oxide, praseodymia, exhibits similar properties, this system is much less studied due to its complex phase diagram. Since both oxides exhibit a flexible structural (polymorphism) and electronic (valence state variation) behavior, it is of ongoing interest to study ceria-praseodymia mixed oxide thin films, in order to tune and improve certain characteristics for the respective applications in the field of microelectronics and catalysis. Goal: Therefore, the goal of this doctoral thesis is to grow and characterize in an interdisziplinary approach single crystalline and epitaxial, binary and ternary Ce1-xPrxO2-δ thin films in order to allocate high quality samples for further fundamental studies, devoted to the structural and electronic properties in the field of microelectronics and catalysis. Experimental: Such single crystalline and epitaxial Ce1-xPrxO2-δ thin films were grown on a Si(111) substrate by molecular beam epitaxy. An in-situ control of the crystal growth quality was achieved by reflection high-energery electron diffraction. A detailed structure characterization study was carried out by laboratory and synchrotron based X-ray scattering. Additionally, transmission electron microscopy gives a highly resolved structural insight. The structural characterization was supported by theoretical ab-initio calculations. To determine the stoichiometries and valence states of the ternary mixed oxide compounds, X-ray photoelectron spectroscopy was performed. The microscopic defect structure was investigated by Raman spectroscopy. Finally, a first insight into the catalytic behavior is gained by temperature programmed desorption experiments. Results: The structural investigation implicates an epitaxial, twin-free, exclusively type-B oriented CeO2(111) growth on Si(111) by using an ultra-thin hex-Pr2O3(0001) buffer layer. This became possible due to the crystallographic continuation of the oxygen sub-lattice and electronic conservation of the semiconducting behavior at the ceria/praseodymia interface. A stabilization of Pr4+ cations is predicted by ab-initio calculations to support this interface transition. On such a hex-Pr2O3(0001)/Si(111) support the growth of epitaxial ternary Ce1-xPrxO2-δ mixed oxides became also possible. A stoichiometry dependent study also implicates an interplay of the structural and electronic properties. In dependency on the Pr content, it turned out that truly mixed alloys with Pr3+ incorporation into the CeO2 fluorite crystal matrix and Ce3+ incorporation into the hex-Pr2O3 matrix were achieved. Between both extremes, it is shown that the Pr content leads to a higher tendency to form Ce3+ cations within a bixbyite lattice, but fluorite inclusions could not be excluded. In a first temperature dependent study on the reduction behavior, it was demonstrated by the linearly increasing behavior of the integral O2 desorption signal and the total lattice spacing difference of heated Ce1-xPrxO2-δ mixed oxides that the oxygen storage capacity can be tailored by Pr doping due to the Pr4+/Pr3+ redox system. Furthermore, it was found that the hydrocarbon oxidation process is mainly triggered by the Ce4+/Ce3+ redox system, since the desorption temperature of CO2 decreased with increasing Ce content. Outlook: In terms of future investigations, such epitaxial single crystalline Ce1-xPrxO2-δ/Si(111) heterostructures are of interest in both research fields, catalysis and microelectronics. They can be used as model catalytic systems in order to gain a deeper understanding of the structure and electronic correlation with the reaction mechanisms by a stepwise increasing of the systems complexity under defined reaction conditions. Furthermore, new applications of such a system might be evaluated in the field of microelectronics. Oxygen vancancy engineering is currently discussed in such rare earth oxides to explain and establish room temperature ferromagnetism phenomena in the area of spintronics.}, subject = {Seltenerdoxide; Heteroepitaxie; D{\"u}nnschichttechnik; Seltenerd-Oxide; Si(111); Heteroepitaktische D{\"u}nnfilme; Ceroxid; Praseodymiumoxid; Rare-earth oxides; Si(111); Heteroepitaxial thin films; Ceria; Praseodymia}, language = {de} }