Berlin 2012 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 27: Thin film characterization: structure analysis and composition (post growth analysis XRD, etc..)
DS 27.2: Vortrag
Mittwoch, 28. März 2012, 16:45–17:00, H 2032
Structural properties of MBE-grown Bi2SexTe3−x layers — •Steffen Schreyeck1, Christian Kehl1, Nadezda V. Tarakina1, Tanja Borzenko1, Claus Schumacher1, Grzegorz Karczewski2, Jean Geurts1, Karl Brunner1, and Laurens W. Molenkamp1 — 1Universität Würzburg, Experimentelle Physik III, Würzburg, Germany — 2Institute of Physics, Polish Academy of Sciences, Warsaw, Poland
Bi2SexTe3−x (V2VI3) alloy layers, a material system with topological insulator (TI) properties, were grown by molecular beam epitaxy on H-passivated Si(111) at TS=300∘C. We varied the Se-flux at constant Bi- and Te-flux to obtain Bi2SexTe3−x samples with x ranging from 0 to 3 (flux ratio VI/V from 24 to 65). The crystal forms quintuple layers (QLs) VI(2)-V-VI(1)-V-VI(2), with Van-der-Waals bonds between the QLs. The streaky RHEED patterns, TEM and high-resolution X-ray diffraction (HRXRD) show good crystal quality for all compositions. The Se content x was determined by HRXRD assuming validity of Vegard’s law. A comparison of flux ratios yield a highly preferred incorporation of Se rather than Te. Lattice dynamics was analysed by Raman spectroscopy from the even-symmetry optical phonon modes Eg(2), A1g(1) and A1g(2). The mode frequencies are essentially determined by the atomic masses in the VI(2) positions and by the V-VI bonding forces. The essentially constant mode frequencies for Se-content x between 0 and 1 strongly indicate a preferential incorporation of Se in the VI(1) position, which is not involved in the vibrational motion, i.e. the realisation of an ordered Bi2SeTe2 phase (Te-Bi-Se-Bi-Te).