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Author: Trampert, Achim × DDC: 540 ×

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    Strategies for Analyzing Noncommon-Atom Heterovalent Interfaces: The Case of CdTe-on-InSb
    (Weinheim : Wiley-VCH, 2019) Luna, Esperanza; Trampert, Achim; Lu, Jing; Aoki, Toshihiro; Zhang, Yong-Hang; McCartney, Martha R.; Smith, David J.
    Semiconductor heterostructures are intrinsic to a wide range of modern-day electronic devices, such as computers, light-emitting devices, and photodetectors. Knowledge of chemical interfacial profiles in these structures is critical to the task of optimizing the device performance. This work presents an analysis of the composition profile and strain across the noncommon-atom heterovalent CdTe/InSb interface, carried out using a combination of electron microscopy imaging techniques. Because of the close atomic numbers of the constituent elements, techniques such as high-angle annular-dark-field and large-angle bright-field scanning transmission electron microscopy, as well as electron energy-loss spectroscopy, give results from the interface region that are inherently difficult to interpret. By contrast, use of the 002 dark-field imaging technique emphasizes the interface location by comparing differences in structure factors between the two materials. Comparisons of experimental and simulated CdTe-on-InSb profiles reveal that the interface is structurally abrupt to within about 1.5 nm (10–90% criterion), while geometric phase analysis based on aberration-corrected electron microscopy images reveals a minimal level of interfacial strain. The present investigation opens new routes to the systematic investigation of heterovalent interfaces, formed by the combination of other valence-mismatched material systems. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    In Situ Transmission Electron Microscopy of Disorder–Order Transition in Epitaxially Stabilized FeGe2
    (Washington, DC : Soc., 2021) Terker, Markus; Nicolai, Lars; Gaucher, Samuel; Herfort, Jens; Trampert, Achim
    Isothermal crystallization of amorphous Ge deposited on a cubic Fe3Si/GaAs(001) substrate is performed by in situ annealing within a transmission electron microscope. It was found that the formation of epitaxially aligned tetragonal FeGe2 is associated with a disorder–order phase transition mainly consisting of a rearrangement of the Fe/vacancy sublattice from a random distribution to alternating filled and empty layers. Additionally, atomically resolved high-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy demonstrated that the vertical lattice spacing of the Ge sublattice reduces across vacancy layers, indicating that strain minimization plays a role in the phase transition process. Crystallization and ordering are both found to proceed layer-by-layer and with square-root-shaped kinetics with a smaller transition rate for the latter.