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| Home > Publications database > Investigation of 2D materials using low energy electron microscopy (LEEM) |
| Dissertation / PhD Thesis | FZJ-2025-04648 |
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2025
RWTH Aachen University
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Please use a persistent id in citations: doi:10.18154/RWTH-2025-07835
Abstract: Low-energy electron microscopy (LEEM) is a versatile and powerful surface science tool for imaging, structural analysis and the study of kinetic surface processes such as molecular island growth, thin film growth and surface reconstruction. It uses electrons with kinetic energies below a few hundred electronvolts, often below 10 eV. In this thesis, LEEM serves as the main technique to support our research efforts in fabricating 30◦-twisted bilayer graphene (TBG) and in studying the deposition and degradation behavior of a cyclic, tire-shaped molecules on a metal crystal. The first two topics of this thesis build on previous work from our group that demonstrated the epitaxial growth of unconventionally oriented monolayer graphene on a 6H-SiC(0001) substrate. In the first topic, LEEM and other investigation methods were used to characterize the morphology and electronic properties of such unconventionally oriented monolayer graphene. The effect of the preparation temperature on the resulting graphene sample was highlighted. In the second topic, we achieved and studied bilayer stacking and twist configurations of graphene by hydrogen intercalation of the carbon buffer layer, an intrinsic component between the epitaxial graphene and the SiC substrate. Hydrogen atoms were successfully introduced to decouple the buffer layer from the substrate. The buffer layer was transformed into a true graphene layer with distinct π-band properties. This intercalation process was carried out in a stepwise manner, with LEEM being used to study each step. The deintercalation process was monitored in situ and in real time. This provided deeper insights into the mechanisms of hydrogen intercalation and deintercalation. In the third topic of the thesis, the deposition behavior of a carbon-based cyclic aromatic molecule, [6]-cycloparaphenylenes, is investigated using LEEM in addition to pristine 2D graphene layers. Interestingly, our observations contradict previous results obtained by scanning tunneling microscopy. This provides new insights into the deposition behavior of this type of molecules on surfaces.
Keyword(s): Hochschulschrift ; twisted bilayer graphene (TBG) ; unconventionally oriented epitaxial graphene ; low energy electron microscopy (LEEM) ; hydrogene intercalation
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