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End date: 2024 × End date: 2014 × Start date: 2013 × DDC: 540 × Type: Text × WGL Institute: IHP ×

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    Oxygen-deficient oxide growth by subliming the oxide source material: The cause of silicide formation in rare earth oxides on silicon
    (Washington, DC : ACS, 2013) Bierwagen, O.; Proessdorf, A.; Niehle, M.; Grosse, F.; Trampert, A.; Klingsporn, M.
    The fundamental issue of oxygen stoichiometry in oxide thin film growth by subliming the source oxide is investigated by varying the additionally supplied oxygen during molecular beam epitaxy of RE2O3 (RE = Gd, La, Lu) thin films on Si(111). Supplying additional oxygen throughout the entire growth was found to prevent the formation of rare earth silicides observed in films grown without an oxygen source. Postgrowth vacuum annealing of oxygen stoichiometric films did not lead to silicide formation thereby confirming that the silicides do not form as a result of an interface instability at growth temperature in vacuum but rather due to an oxygen deficiency in the source vapor. The average oxygen deficiency of the rare-earth containing species in the source vapor was quantified by the 18O tracer technique and correlated with that of the source material, which gradually decomposed during sublimation. Therefore, any oxide growth by sublimation of the oxide source material requires additional oxygen to realize oxygen stoichiometric films.
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    Modeling the shape of ions in pyrite-type crystals
    (Basel : MDPI, 2014) Birkholz, Mario
    The geometrical shape of ions in crystals and the concept of ionic radii are re-considered. The re-investigation is motivated by the fact that a spherical modelling is justified for p valence shell ions on cubic lattice sites only. For the majority of point groups, however, the ionic radius must be assumed to be an anisotropic quantity. An appropriate modelling of p valence ions then has to be performed by ellipsoids. The approach is tested for pyrite-structured dichalcogenides MX2, with chalcogen ions X = O, S, Se and Te. The latter are found to exhibit the shape of ellipsoids being compressed along the <111> symmetry axes, with two radii r