In situ-Studien zu Wachstum und Struktur seltenerdoxidbasierter inverser Modellkatalysatoren

Rare earth oxides in combination with transition metals are under intense investigation due to their versatile catalytic properties. Even though especially ceria is already successfully used in today's catalytic converters, many fundamental aspects of their active role in catalytic processes are still unclear. Using well-defined metal-on-oxide and so-called inverse oxide-on-metal model catalysts is a widely accepted approach to gain insights into the active nature of rare earth oxides. Whereas the preparation of (111) oriented rare earth oxide inverse model catalysts are quite standard today, the synthesis of inverse model catalysts with different orientations, which are suspected to be different in activity and selectivity in chemical reactions, on well established transition metal surfaces is still challenging. Enabled by time-resolved low-energy electron microscopy the reactive growth of the rare earth oxides of cerium and terbium on Cu(111) as well as the growth of ceria on Ru(0001) are investigated. Both oxides grow on the Cu(111) surface in a Volmer-Weber growth mode but in two different orientations: ceria islands exhibit (100) and (111) oriented surfaces, terbia islands grow in (112) and (111) orientation. It is demonstrated that growth of CeO2 (100) on Cu(111) depends on the Ce/O ratio on the substrate surface, permitting the exclusive growth of CeO2(100) in the low Ce/O regime and exclusive growth of CeO2 (111) in the high regime. In case of terbia a favorable lattice matching enabled by a coincidence of the TbOx (112) unit cell with the Cu(111) unit cell was supposed to facilitate formation of the high- index surface. In addition, the emergence of CeO2 (100) on Ru(0001) is presented, which is also attributed to the local oxygen chemical potential. These findings illustrate that it is possible to manipulate the orientation of rare earth oxide surfaces, which can be applied to synthesize new kinds of model catalysts. The reactivity and selectivity of ceria not only depends on the orientation of the ceria surface but also on the presence of oxygen vacancies. Thus stable phases and phase transitions from CeO2 to Ce2O3 are of special interest to understand cerias catalytic properties. Observing structural changes during hydrogen reduction of ceria grown on ruthenium in real-time using low-energy electron microscopy and micro electron diffraction as well as micro x-ray absorption spectroscopy reveal the formation of ordered oxygen vacancies. Moreover three stable phases, which coexist for intermediate oxidation states, demonstrate a spatially varying stoichiometry of the ceria surface during reduction. These results shed new light on the changes of structure in chemical reactions, which have to be considered in view of structure-function relationship

Prospects for the Measurement of the Higgs Yukawa Couplings to b and c quarks, and muons at CLIC

The investigation of the properties of the Higgs boson, especially a test of the predicted linear dependence of the branching ratios on the mass of the final state is going to be an integral part of the physics program at colliders at the energy frontier for the foreseeable future. The large Higgs boson production cross section at a 3TeV CLIC machine allows for a precision measurement of the Higgs branching ratios. The cross section times branching ratio of the decays H->bb, H->cc and H->{\mu}{\mu} of a Standard Model Higgs boson with a mass of 120 GeV can be measured with a statistical uncertainty of 0.23%, 3.1% and 15%, respectively, assuming an integrated luminosity of 2 ab-1.Comment: 6 pages, 4 figure

The Extended Postoperative Care-Score (EXPO-Score)-An Objective Tool for Early Identification of Indication for Extended Postoperative Care

Extended postoperative care and intensive care unit capacity is limited and efficient patient allocation is mandatory. This study aims to develop an effective yet simple score to predict indication for extended postoperative care, as there is a lack of objective criteria for early prediction of admission to extended care in surgical patients. This prospective observational study was divided into two periods (Period 1: Extended Postoperative Care-Score (EXPO)-Score generation; Period 2: EXPO-Score validation) and it was performed at a tertiary university center in Germany. A total of 4042 (Period 1) and 2198 (Period 2) adult patients ≥ 18 years old receiving elective or emergency surgery were included in this study. After identifying patient- and surgery-related risk factors by an expert panel, the EXPO-Score was developed through logistic regression from data of Period 1 and validated in Period 2. Three risk factors are sufficient for generating a reliable predictive EXPO-Score: (1) the American Society of Anesthesiologists' (ASA) physical status, (2) cardiopulmonary physical exercise status expressed in metabolic equivalents (MET), and (3) the type of surgery. The score threshold (0.23) has a sensitivity of 0.87, a specificity of 0.91, and an accuracy of 0.90 for predicting indication for extended postoperative care. The EXPO-Score provides a validated, early collectable, and easy-to-use tool for predicting indication of extended postoperative care in adult surgical patients

In situ studies of growth and structure of rare-earth oxide based inverse model catalysts

Rare earth oxides in combination with transition metals are under intense investigation due to their versatile catalytic properties. Even though especially ceria is already successfully used in today's catalytic converters, many fundamental aspects of their active role in catalytic processes are still unclear. Using well-defined metal-on-oxide and so-called inverse oxide-on-metal model catalysts is a widely accepted approach to gain insights into the active nature of rare earth oxides. Whereas the preparation of (111) oriented rare earth oxide inverse model catalysts are quite standard today, the synthesis of inverse model catalysts with different orientations, which are suspected to be different in activity and selectivity in chemical reactions, on well established transition metal surfaces is still challenging. Enabled by time-resolved low-energy electron microscopy the reactive growth of the rare earth oxides of cerium and terbium on Cu(111) as well as the growth of ceria on Ru(0001) are investigated. Both oxides grow on the Cu(111) surface in a Volmer-Weber growth mode but in two different orientations: ceria islands exhibit (100) and (111) oriented surfaces, terbia islands grow in (112) and (111) orientation. It is demonstrated that growth of CeO2 (100) on Cu(111) depends on the Ce/O ratio on the substrate surface, permitting the exclusive growth of CeO2(100) in the low Ce/O regime and exclusive growth of CeO2 (111) in the high regime. In case of terbia a favorable lattice matching enabled by a coincidence of the TbOx (112) unit cell with the Cu(111) unit cell was supposed to facilitate formation of the high- index surface. In addition, the emergence of CeO2 (100) on Ru(0001) is presented, which is also attributed to the local oxygen chemical potential. These findings illustrate that it is possible to manipulate the orientation of rare earth oxide surfaces, which can be applied to synthesize new kinds of model catalysts. The reactivity and selectivity of ceria not only depends on the orientation of the ceria surface but also on the presence of oxygen vacancies. Thus stable phases and phase transitions from CeO2 to Ce2O3 are of special interest to understand cerias catalytic properties. Observing structural changes during hydrogen reduction of ceria grown on ruthenium in real-time using low-energy electron microscopy and micro electron diffraction as well as micro x-ray absorption spectroscopy reveal the formation of ordered oxygen vacancies. Moreover three stable phases, which coexist for intermediate oxidation states, demonstrate a spatially varying stoichiometry of the ceria surface during reduction. These results shed new light on the changes of structure in chemical reactions, which have to be considered in view of structure-function relationship

Thermal reduction of ceria nanostructures on rhodium(111) and re-oxidation by CO2

The thermal reduction of cerium oxide nanostructures deposited on a rhodium(111) single crystal surface and the re-oxidation of the structures by exposure to CO2 were investigated. Two samples are compared: a rhodium surface covered to ≈60% by one to two O-Ce-O trilayer high islands and a surface covered to ≈65% by islands of four O-Ce-O trilayer thickness. Two main results stand out: (1) the thin islands reduce at a lower temperature (870-890 K) and very close to Ce2O3, while the thicker islands need higher temperature for reduction and only reduce to about CeO1.63 at a maximum temperature of 920 K. (2) Ceria is re-oxidized by CO2. The rhodium surface promotes the re-oxidation by splitting the CO2 and thus providing atomic oxygen. The process shows a clear temperature dependence. The maximum oxidation state of the oxide reached by re-oxidation with CO2 differs for the two samples, showing that the thinner structures require a higher temperature for re-oxidation with CO2. Adsorbed carbon species, potentially blocking reactive sites, desorb from both samples at the same temperature and cannot be the sole origin for the observed differences. Instead, an intrinsic property of the differently sized CeOx islands must be at the origin of the observed temperature dependence of the re-oxidation by CO2

Ultrathin, epitaxial cerium dioxide on silicon

It is shown that ultrathin, highly ordered, continuous films of cerium dioxide may be prepared on silicon following substrate prepassivation using an atomic layer of chlorine. The as-deposited, few-nanometer-thin Ce2O3 film may very effectively be converted at room temperature to almost fully oxidized CeO2 by simple exposure to air, as demonstrated by hard X-ray photoemission spectroscopy and X-ray diffraction. This post-oxidation process essentially results in a negligible loss in film crystallinity and interface abruptness