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Electron-beam-induced modifications in two-dimensional materials

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Dissertation_Lehnert ... (54.86Mb)
Erstveröffentlichung
2020-07-13
Authors
Lehnert, Tibor
Referee
Kaiser, Ute
Meyer, Jannik
Dissertation


Faculties
Fakultät für Naturwissenschaften
Institutions
ZE Elektronenmikroskopie
Abstract
Electron-beam-induced structural modifications were studied in high-resolution transmission electron microscopy (TEM) images of the two-dimensional (2D) transition metal dichalcogenides (TMDs) MoS2, MoSe2 and MoTe2 as well as graphene liquid cells embedding thin NaCl and CaSO4 crystals. Studies on MoS2, MoSe2 and graphene liquid cells were performed using a Cs-corrected TEM operated at an electron acceleration voltage of 80 kV. Further experiments on MoS2 and MoTe2 were performed using the newly developed chromatic (Cc) and spherical (Cs) aberration-corrected Sub-Ångström Low-Voltage Electron microscope (SALVE) operated at voltages from 80 kV down to 20 kV. Voltage-dependent damage rates in MoS2 and MoSe2 below the knock-on threshold revealed that atomic defect creation can only be explained by a two-step process, starting with electronic excitations and followed by ballistic collisions. Additionally, structural determination of produced defects in MoTe2 - combined with density functional theory - exhibited local change of electronic properties. Within this work it was also shown that graphene encapsulations significantly increase the stability of TMDs against electron-beam irradiation. Therefore, graphene was also used as encapsulating material to study ionic crystals such as CaSO4 and NaCl in liquid cells. Due to the crystallization of CaSO4, pressure and temperature conditions within the graphene liquid cell were estimated via a superposition of p-T phase diagrams combined with thickness-dependent transition temperatures. Moreover, the decomposition of NaCl crystals in graphene liquid cells was followed. This revealed that the encapsulated material is only stable as long as the protecting graphene is undamaged and that a first defect in graphene initiate already an immediate decomposition of the NaCl crystals.
Date created
2019
Cumulative dissertation containing articles
• Tibor Lehnert, Ossi Lehtinen, Gerardo Algara-Siller, Ute Kaiser, 2017. Electron radiation damage mechanisms in 2D MoSe2, In: Applied Physics Letters 18.01.2017. 110, 033106 [Zugriff: 03.04.2019] Verfügbar unter: https://doi.org/10.1063/1.4973809
• Silvan Kretschmer, Tibor Lehnert, Ute Kaiser, Arkady Krasheninnikov, 2020. Formation of Defects in Two-Dimensional MoS2 in the Transmission Electron Microscope at Electron Energies below the Knock-on Threshold: The Role of Electronic Excitations, In: Nano Letters 20.03.2020. 20, 2865-2870 [Zugriff: 08.04.2020] Verfügbar unter: https://doi.org/10.1021/acs.nanolett.0c00670
• Tibor Lehnert, Mahdi Ghorbani-Asl, Janis Köster, Zhongbo Lee, Arkady V. Krasheninnikov, Ute Kaiser, 2019. Electron-Beam-Driven Structure Evolution of Single-Layer MoTe2 for Quantum Devices, In: ACS Applied Nano Materials 26.04.2019, 2, 3262-3270 [Zugriff: 24.05.2019] Verfügbar unter: https://doi.org/10.1021/acsanm.9b00616
• Tibor Lehnert, Michael K. Kinyanjui, Anita Ladenburger, Dimitri Rommel, Katharina Wörle, Felix Börrnert, Kerstin Leopold, Ute Kaiser, 2017. In Situ Crystallization of Insoluble Anhydrite AII Phase in Graphene Pockets, In: ACS Nano 24.07.2017, 11, 7967-7973 [Zugriff: 03.04.2019] Verfügbar unter: https://doi.org/10.1021/acsnano.7b02513
Subject headings
[LCSH]: Electron beams | Transmission electron microscopy | Nanostructures
[Free subject headings]: HRTEM | 2D materials | transition metal dichalcogenides | radiation damage | graphene liquid cells
[DDC subject group]: DDC 540 / Chemistry & allied sciences
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https://oparu.uni-ulm.de/xmlui/license_v3

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DOI & citation

Please use this identifier to cite or link to this item: http://dx.doi.org/10.18725/OPARU-32253

Lehnert, Tibor (2020): Electron-beam-induced modifications in two-dimensional materials. Open Access Repositorium der Universität Ulm und Technischen Hochschule Ulm. Dissertation. http://dx.doi.org/10.18725/OPARU-32253
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