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Author: Büchner, Bernd × End date: 2023 × DDC: 540 × DDC: 660 × WGL Institute: IFWD ×

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Now showing 1 - 3 of 3
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    Single-Molecule Magnets DyM2N@C80 and Dy2MN@C80 (M=Sc, Lu): The Impact of Diamagnetic Metals on Dy3+ Magnetic Anisotropy, Dy⋅⋅⋅Dy Coupling, and Mixing of Molecular and Lattice Vibrations
    (Weinheim : Wiley-VCH, 2020) Spree, Lukas; Schlesier, Christin; Kostanyan, Aram; Westerström, Rasmus; Greber, Thomas; Büchner, Bernd; Avdoshenko, Stanislav M.; Popov, Alexey A.
    The substitution of scandium in fullerene single-molecule magnets (SMMs) DySc2N@C80 and Dy2ScN@C80 by lutetium has been studied to explore the influence of the diamagnetic metal on the SMM performance of dysprosium nitride clusterfullerenes. The use of lutetium led to an improved SMM performance of DyLu2N@C80, which shows a higher blocking temperature of magnetization (TB=9.5 K), longer relaxation times, and broader hysteresis than DySc2N@C80 (TB=6.9 K). At the same time, Dy2LuN@C80 was found to have a similar blocking temperature of magnetization to Dy2ScN@C80 (TB=8 K), but substantially different interactions between the magnetic moments of the dysprosium ions in the Dy2MN clusters. Surprisingly, although the intramolecular dipolar interactions in Dy2LuN@C80 and Dy2ScN@C80 are of similar strength, the exchange interactions in Dy2LuN@C80 are close to zero. Analysis of the low-frequency molecular and lattice vibrations showed strong mixing of the lattice modes and endohedral cluster librations in k-space. This mixing simplifies the spin–lattice relaxation by conserving the momentum during the spin flip and helping to distribute the moment and energy further into the lattice. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
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    Three-Dimensional Composition and Electric Potential Mapping of III–V Core–Multishell Nanowires by Correlative STEM and Holographic Tomography
    (Washington, DC : ACS Publ., 2018-7-13) Wolf, Daniel; Hübner, René; Niermann, Tore; Sturm, Sebastian; Prete, Paola; Lovergine, Nico; Büchner, Bernd; Lubk, Axel
    The nondestructive characterization of nanoscale devices, such as those based on semiconductor nanowires, in terms of functional potentials is crucial for correlating device properties with their morphological/materials features, as well as for precisely tuning and optimizing their growth process. Electron holographic tomography (EHT) has been used in the past to reconstruct the total potential distribution in three-dimension but hitherto lacked a quantitative approach to separate potential variations due to chemical composition changes (mean inner potential, MIP) and space charges. In this Letter, we combine and correlate EHT and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) tomography on an individual ⟨111⟩ oriented GaAs–AlGaAs core–multishell nanowire (NW). We obtain excellent agreement between both methods in terms of the determined Al concentration within the AlGaAs shell, as well as thickness variations of the few nanometer thin GaAs shell acting as quantum well tube. Subtracting the MIP determined from the STEM tomogram, enables us to observe functional potentials at the NW surfaces and at the Au–NW interface, both ascribed to surface/interface pinning of the semiconductor Fermi level.
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    Thermoelectric Properties of Novel Semimetals: A Case Study of YbMnSb2
    (Weinheim : Wiley-VCH, 2020) Pan, Yu; Fan, Feng-Ren; Hong, Xiaochen; He, Bin; Le, Congcong; Schnelle, Walter; He, Yangkun; Imasato, Kazuki; Borrmann, Horst; Hess, Christian; Büchner, Bernd; Sun, Yan; Fu, Chenguang; Snyder, G. Jeffrey; Felser, Claudia
    The emerging class of topological materials provides a platform to engineer exotic electronic structures for a variety of applications. As complex band structures and Fermi surfaces can directly benefit thermoelectric performance it is important to identify the role of featured topological bands in thermoelectrics particularly when there are coexisting classic regular bands. In this work, the contribution of Dirac bands to thermoelectric performance and their ability to concurrently achieve large thermopower and low resistivity in novel semimetals is investigated. By examining the YbMnSb2 nodal line semimetal as an example, the Dirac bands appear to provide a low resistivity along the direction in which they are highly dispersive. Moreover, because of the regular-band-provided density of states, a large Seebeck coefficient over 160 µV K−1 at 300 K is achieved in both directions, which is very high for a semimetal with high carrier concentration. The combined highly dispersive Dirac and regular bands lead to ten times increase in power factor, reaching a value of 2.1 mW m−1 K−2 at 300 K. The present work highlights the potential of such novel semimetals for unusual electronic transport properties and guides strategies towards high thermoelectric performance. © 2020 The Authors. Advanced Materials published by Wiley-VCH GmbH