The new third-generation synchrotron radiation source PETRA III located at the Deutsches Elektronen-Synchrotron DESY in Hamburg, Germany, has been operational since the second half of 2009. PETRA III is designed to deliver hard X-ray beams with very high brilliance. As one of the first beamlines of PETRA III the high-resolution diffraction beamline P08 is fully operational. P08 is specialized in X-ray scattering and diffraction experiments on solids and liquids where extreme high resolution in reciprocal space is required. The resolving power results in the high-quality PETRA III beam and unique optical elements such as a large-offset monochromator and beryllium lens changers. A highprecision six-circle diffractometer for solid samples and a specially designed liquid diffractometer are installed in the experimental hutch. Regular users have been accepted since summer 2010.
A film of praseodymium sesquioxide with hexagonal structure, that has been deposited on Si͑111͒ by molecular beam epitaxy, was annealed in oxygen atmosphere to obtain a PrO 2 film for improved heteroepitaxy as buffer dielectric for alternative semiconductor layer integration. The film structure is characterized by x-ray diffraction and x-ray reflectometry. The film is single crystalline with Fm3m ͑fluorite͒ structure. It is B oriented with respect to Si and has lattice constants close to bulk PrO 2 . The cubic lattice of the PrO 2 film is slightly distorted due to residual oxygen vacancies which increase the diameter of Pr ions.
Ultra thin heteroepitaxial PrO(2) films on Si(111) were annealed under UHV conditions and investigated by x-ray diffraction (XRD), x-ray reflectometry (XRR) and spot profile analysis low energy electron diffraction (SPALEED) with regard to structural stability and phase transitions due to the high oxygen mobility of the oxide. This gives information about the manageability of the material and its application as a model catalyst system in surface science. While the samples are stable in UHV at room temperature, annealing at 300 °C exhibits a terminated phase transition from PrO(2) and PrO(2-Δ) to cub-Pr(2)O(3) with an increase in the silicate at the interface and a decrease in the crystalline praseodymia layer mainly due to atomic diffusion of silicon into the oxide film. Strain effects during the phase transition also cause mosaic formation at the surface. Further annealing up to 600 °C shows only little change in the film structure. This will finally lead to a model of the film structure during the annealing process.
A combined structure and stoichiometry study on the growth behavior of single crystalline Ge(111) layers on PrO2(111)∕Si(111) heterostructures is presented. Ex situ x-ray diffraction techniques indicate that the interaction between Ge and PrO2(111) results in a complete reduction of the buffer oxide to a cubic Pr2O3(111) film structure. In situ reflection high energy electron diffraction, x-ray and ultraviolet photoelectron spectroscopy studies demonstrate that this chemical reduction of the oxide support occurs during the initial Ge growth stage. The interaction of PrO2 with Ge results in the formation of an amorphous Ge oxide layer by the diffusion of lattice oxygen from the dielectric to the forming semiconductor deposit. After the complete conversion of PrO2 to cubic Pr2O3, the supply of reactive lattice oxygen is exhausted and the continuous Ge deposition reduces the initially formed amorphous GeO2-like film to GeO. The sublimation of volatile GeO uncovers the single crystalline cubic Pr2O3(111) film surface which provides a thermodynamically stable template for elemental Ge heteroepitaxy. A Volmer–Weber growth mode is observed which results after island coalescence in the formation of atomically smooth, single crystalline Ge(111) layers.
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