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Energy-filtered TEM and low-loss EELS of 2D materials

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Mohn_2020_OPARU.pdf (11.73Mb)
Erstveröffentlichung
2020-11-19
DOI
10.18725/OPARU-33799
Dissertation


Authors
Mohn, Michael Johannes
Referee
Kaiser, Ute
Koch, Christoph T.
Faculties
Fakultät für Naturwissenschaften
Institutions
ZE Elektronenmikroskopie
License
Standard
https://oparu.uni-ulm.de/xmlui/license_v3
Abstract
In this work, we perform aberration-corrected energy-filtered TEM (EFTEM) and low-loss electron energy-loss spectroscopy (EELS) with two-dimensional (2D) materials. In particular, the carbon K-edge EFTEM signal is analyzed for a monolayer of graphene, and the low-loss EELS spectra of graphene and molybdenum disulfide (MoS₂) heterostructures are investigated by the technique of momentum-resolved EELS. With EFTEM in the Cc/Cs-corrected “SALVE III” low-voltage transmission electron microscope, we demonstrate lattice contrast in zero-loss, plasmon-loss, and C-K-edge images. Both bright-atom contrast and dark-atom contrast are observed in all three cases, and focus series show that even for the C-K edge, contrast inversions can be caused by a change in the defocus. For an analysis of the image contrast in direct space, all raw EFTEM data are averaged over a large number of unit cells to improve the signal-to-noise-ratio. In the low-loss regime of EELS (0–50 eV), our momentum-resolved experimental data for 2D heterostructures of graphene and MoS₂ can be understood by a combination of ab initio simulations and dielectric model calculations. Therefore, the low-loss EELS signals of 2D multilayers and heterostructures are described on the basis of time-dependent density functional theory calculations for the constituent monolayers. Expanding on a layered-electron gas model for graphene, multilayers and heterostructures with MoS₂ are eventually modeled by microscopic dielectric calculations that are in good agreement with our experimental EELS data. The necessity of models beyond the layered electron-gas model is demonstrated by calculations for multilayer and bulk MoS₂.
Date created
2020
Funding information
SPP 1459 Teilprojekt / Manipulation und Charakterisierung von strukturellen Eigenschaften des Graphens / DFG / SPP/ 227454087
EU Project
GRAPHENE / Graphene-Based Revolutions in ICT And Beyond / EC / FP7 / 604391
GrapheneCore1 / Graphene-based disruptive technologies / EC / H2020 / 696656
GrapheneCore2 / Graphene Flagship Core Project 2 / EC / H2020 / 785219
Subject Headings
Durchstrahlungselektronenmikroskopie [GND]
Niederdimensionales System [GND]
Graphen [GND]
Heterostruktur [GND]
Dielektrische Eigenschaft [GND]
Plasmon [GND]
Elektronen-Energieverlustspektroskopie [GND]
Transmission electron microscopy [LCSH]
Low-dimensional semiconductors [LCSH]
Graphene [LCSH]
Heterostructures [LCSH]
Dielectrics [LCSH]
Electron energy loss spectroscopy [LCSH]
Density functionals [LCSH]
Keywords
Dichtefunktionalformalismus
Dewey Decimal Group
DDC 530 / Physics

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Mohn, Michael Johannes (2020): Energy-filtered TEM and low-loss EELS of 2D materials. Open Access Repositorium der Universität Ulm. Dissertation. http://dx.doi.org/10.18725/OPARU-33799

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