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Author: Ruck, Michael × DDC: 530 ×

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    Layered manganese bismuth tellurides with GeBi4Te7- and GeBi6Te10-type structures: Towards multifunctional materials
    (London : RSC Publ., 2019) Souchay, Daniel; Nentwig, Markus; Günther, Daniel; Keilholz, Simon; de Boor, Johannes; Zeugner, Alexander; Isaeva, Anna; Ruck, Michael; Wolter, Anja U.B.; Büchnerde, Bernd; Oeckler, Oliver
    The crystal structures of new layered manganese bismuth tellurides with the compositions Mn0.85(3)Bi4.10(2)Te7 and Mn0.73(4)Bi6.18(2)Te10 were determined by single-crystal X-ray diffraction, including the use of microfocused synchrotron radiation. These analyses reveal that the layered structures deviate from the idealized stoichiometry of the 12P-GeBi4Te7 (space group P3m1) and 51R-GeBi6Te10 (space group R3m) structure types they adopt. Modified compositions Mn1-xBi4+2x/3Te7 (x = 0.15-0.2) and Mn1-xBi6+2x/3Te10 (x = 0.19-0.26) assume cation vacancies and lead to homogenous bulk samples as confirmed by Rietveld refinements. Electron diffraction patterns exhibit no diffuse streaks that would indicate stacking disorder. The alternating quintuple-layer [M2Te3] and septuple-layer [M3Te4] slabs (M = mixed occupied by Bi and Mn) with 1 : 1 sequence (12P stacking) in Mn0.85Bi4.10Te7 and 2 : 1 sequence (51R stacking) in Mn0.81Bi6.13Te10 were also observed in HRTEM images. Temperature-dependent powder diffraction and differential scanning calorimetry show that the compounds are high-temperature phases, which are metastable at ambient temperature. Magnetization measurements are in accordance with a MnII oxidation state and point at predominantly ferromagnetic coupling in both compounds. The thermoelectric figures of merit of n-type conducting Mn0.85Bi4.10Te7 and Mn0.81Bi6.13Te10 reach zT = 0.25 at 375 °C and zT = 0.28 at 325 °C, respectively. Although the compounds are metastable, compact ingots exhibit still up to 80% of the main phases after thermoelectric measurements up to 400 °C. © The Royal Society of Chemistry 2019.
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    Strong and Weak 3D Topological Insulators Probed by Surface Science Methods
    (Weinheim : Wiley-VCH, 2020) Morgenstern, Markus; Pauly, Christian; Kellner, Jens; Liebmann, Marcus; Pratzer, Marco; Eschbach, Markus; Plucinski, Lukacz; Otto, Sebastian; Rasche, Bertold; Ruck, Michael; Richter, Manuel; Just, Sven; Lüpke, Felix; Voigtländer, Bert
    The contributions of surface science methods to discover and improve 3D topological insulator materials are reviewed herein, illustrated with examples from the authors’ own work. In particular, it is demonstrated that spin-polarized angular-resolved photoelectron spectroscopy is instrumental to evidence the spin-helical surface Dirac cone, to tune its Dirac point energy toward the Fermi level, and to discover novel types of topological insulators such as dual ones or switchable ones in phase change materials. Moreover, procedures are introduced to spatially map potential fluctuations by scanning tunneling spectroscopy and to identify topological edge states in weak topological insulators. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Influence of chemical interactions on the electronic properties of BiOI/organic semiconductor heterojunctions for application in solution-processed electronics
    (London [u.a.] : RSC, 2023) Lapalikar, Vaidehi; Dacha, Preetam; Hambsch, Mike; Hofstetter, Yvonne J.; Vaynzof, Yana; Mannsfeld, Stefan C. B.; Ruck, Michael
    Bismuth oxide iodide (BiOI) has been viewed as a suitable environmentally-friendly alternative to lead-halide perovskites for low-cost (opto-)electronic applications such as photodetectors, phototransistors and sensors. To enable its incorporation in these devices in a convenient, scalable, and economical way, BiOI thin films were investigated as part of heterojunctions with various p-type organic semiconductors (OSCs) and tested in a field-effect transistor (FET) configuration. The hybrid heterojunctions, which combine the respective functionalities of BiOI and the OSCs were processed from solution under ambient atmosphere. The characteristics of each of these hybrid systems were correlated with the physical and chemical properties of the respective materials using a concept based on heteropolar chemical interactions at the interface. Systems suitable for application in lateral transport devices were identified and it was demonstrated how materials in the hybrids interact to provide improved and synergistic properties. These indentified heterojunction FETs are a first instance of successful incorporation of solution-processed BiOI thin films in a three-terminal device. They show a significant threshold voltage shift and retained carrier mobility compared to pristine OSC devices and open up possibilities for future optoelectronic applications.