Universität zu Köln

Runte, Sven (2013). Atomic and Electronic Structure of Graphene and Graphene Intercalation Compounds. X-Ray Standing Wave and Scanning Tunnelling Microscopy Studies. PhD thesis, Universität zu Köln.

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Abstract

The morphology of graphene/Iridium(111) was studied by x-ray standing wave (XSW) measurements. A dependence of the moire corrugation on the graphene coverage is observed. A comparison with density functional theory (DFT) reveals a discrepancy on the corrugation caused by stress appearing from the cool down from the preparation temperature. The model of rehybridised graphene due to cluster adsorption is supported by a structure analysis. Graphene intercalation compounds were investigated by scanning tunnelling microscopy (STM), low energy electron diffraction (LEED), and XSW. It is shown that intercalation takes place via cracks and holes at wrinkles and wrinkle crossings. The superstructures of caesium intercalated graphene are resolved. For intercalants interacting mainly via van der Waals forces it could be shown that the graphene-intercalant distance is dependent on the charge transfer. Moreover, the structure analysis supports that oxygen intercalation leads to quasi freestanding graphene. A rigid-band model is introduced and applied to graphene intercalation compounds. Scanning tunnelling microscopy measurements reveal clear indications for Dirac electron scattering at defects. In these processes the pseudo-spin is not conserved leading to both inter- and intravalley scattering.