Inelastic H-Atom scattering from ultra-thin films
von Yvonne Jeannette Dorenkamp
Datum der mündl. Prüfung:2018-08-15
Erschienen:2018-09-05
Betreuer:Prof. Dr. Alec Wodtke
Gutachter:Prof. Dr. Alec Wodtke
Gutachter:Prof. Dr. Dirk Schwarzer
Dateien
Name:Y. J. Dorenkamp_eDiss.pdf
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Zusammenfassung
Englisch
This thesis contains experimental and theoretical fundamental studies of energy transfer processes on various surfaces via inelastic hydrogen atom scattering using the Rydberg atom tagging machine. The initial investigations of in total six late transition fcc-metals (Au, Pt, Ag, Pd, Cu, Ni) allowed to establish and optimize the experimental methodology as well as to simultaneously substantiate a theoretical model for the general description of energy-transfer processes on metal surfaces. Hence, it could be determined that the energy transfer for the investigated fcc-metals predominantly takes place via electron-hole-pair excitation. Despite its smaller contribution, phonon excitation was found to be essential in order to describe the experimentally determined (H/D)-isotope effects. During the subsequently performed first hydrogen scattering experiments on insulating bulk as well as thin-layer surfaces, primarily direct inelastic scattering was observed that could be described by simple collision models. The variation of the layer thickness down to less than one monolayer of insulating aluminium oxide did not yield any significant changes of the scattering results, thus, a potential cooperative effect with the platinum substrate have been ruled out. These results as well as the scattering experiments performed on an oxygen covered Pt(111) surface would further suggest that scattering almost exclusively occurs on the quasi-isolated oxygen atoms on the surface. In a concluding series of hydrogen scattering experiments of (1 x 1) oriented graphene and partially rotated graphene on Ni(111), it was possible to study the C-H bond formation process between an impinging hydrogen atom and the graphene surfaces. The experimentally determined adsorption threshold significantly differs for both modification as well as with respect to prior studies of graphene on Pt(111), which could be explained by different interaction strengths between the graphene surface and the metal substrate. In addition, a detailed data analysis of the performed experiments further allowed to assign two new scattering components that previously had not been considered for graphene on Pt(111).
Keywords: Hydrogen Atom Scattering; Surface scattering; fcc transition metals; Thin oxide layer surfaces; Aluminum Oxide; Graphene; Rydberg Atom Tagging