This title appears in the Scientific Report :
2018
Please use the identifier:
http://hdl.handle.net/2128/19179 in citations.
The electronic structure of transition metal dichalcogenides investigated by angle-resolved photoemission spectroscopy
The electronic structure of transition metal dichalcogenides investigated by angle-resolved photoemission spectroscopy
Van der Waals (vdW) materials offer a perspective to revolutionize basically every facet of nowadays technology with a new generation of atomically thin devices. Transition metal dichalcogenides (TMDCs) are a family of vdW crystals, that includes several semiconducting materials with band gaps withi...
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Personal Name(s): | Gehlmann, Mathias (Corresponding author) |
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Contributing Institute: |
Elektronische Eigenschaften; PGI-6 |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2018
|
Physical Description: |
II, 108, 1-XVIII S. |
Dissertation Note: |
Universität Duisburg, Diss., 2018 |
ISBN: |
978-3-95806-324-2 |
Document Type: |
Book Dissertation / PhD Thesis |
Research Program: |
Addenda |
Series Title: |
Schriften des Forschungszentrums Jülich. Reihe Schlüsseltechnologien / Key Technologies
170 |
Link: |
OpenAccess OpenAccess |
Publikationsportal JuSER |
Van der Waals (vdW) materials offer a perspective to revolutionize basically every facet of nowadays technology with a new generation of atomically thin devices. Transition metal dichalcogenides (TMDCs) are a family of vdW crystals, that includes several semiconducting materials with band gaps within the optical range. This makes them ideal for numerous applications such as transistors, optical sensors, solar cells, and LEDs. In this study we focuses on two members of the TMDC family: molybdenum disufide (MoS$_{2}$) and rhenium disulfide (ReS$_{2}$). Using a combination of angle-resolved photoemission spectroscopy (APRES) with density functional theory (DFT), we provide a thorough analysis of the electronic band structure of these two exceptional materials. In monolayers of MoS$_{2}$ the combination of broken inversion symmetry with the heavy element molybdenum leads to a large spin-splitting of distinct valleys within its electronic structure. Therefore, MoS$_{2}$ combines the essential ingredients for socalled $\textit{spintronics}$ and $\textit{valleytronics}$. It was generally believed that these fascinating features are forbidden in MoS$_{2}$ bulk crystals due to their centrosymmetric space group. This study demonstrates that the strong confinement of the valleys within the vdW layers leads to a recently discovered type of $\textit{hidden spin-polarization}$, which results in quasi two-dimensional, highly spin-polarized states in this centrosymmetricbulk crystal. Furthermore, we present the first ARPES study of ReS$_{2}$ bulk, monolayer, and bilayer crystals. Recent literature reported indications for a total confinement of the bulk electronic structure within the plains of the vdW layers. Our study comes to the opposite conclusion. Based on the observation of a considerable out-of-plane dispersion in the ARPES experiments, as well as in the band structure calculations, we show that valence electrons are significantly delocalized across the vdW gap. In addition, we identify the valence band maximum of bulk, monolayer, and bilayer ReS$_{2}$ experimentally. The combination of ARPES and band structure calculations shows that ReS$_{2}$ undergoes a transition from a direct band gap in the bulk and bilayer to an indirect gap in the monolayer. |