Scanning tunneling microscopy and femtosecond laser photoemission spectroscopy of supported cluster structures: A new experimental approach
FacultiesFakultät für Naturwissenschaften
The objective of the present thesis was to design a novel experimental setup for the investigation of the physical and chemical properties of solid surfaces covered by metal clusters applying scanning tunneling microscopy (STM) and femtosecond laser photoemission spectroscopy (PES). This combination of analytical techniques provides the possibility to monitor surface characteristics with spatial resolution on one and temporal resolution on the other hand. The unique support system of a graphene layer grown onto an Ir(111) single crystal surface was applied to prepare monodisperse Ir clusters lattices with extensions from a few atoms to the nanometer scale. The influence of the parameters cluster size and cluster separation on the unoccupied electronic state structure of the substrate was systematically investigated. The Ir clusters were found to affect the image potential states of the surface to an extent which is surprisingly large compared to the covered graphene area. This effect was related to the influence of the Ir clusters on the screening of the image state electron trapped in front of the surface. In a next set of experiments the adsorption of two different organosulfur molecules, namely butanethiol and 3-bromothiophenol, on the Ir(111)/graphene/Ir cluster system was studied via the combination of PES and STM. Both selected thiols were found to exhibit a geometric adsorption pattern, which is identical for the molecule adsorption on the bare Ir(111) surface and on the Ir clusters, respectively. However, a detailed STM image analysis found the two different molecules investigated to exhibit distinctly different adsorption.
Subject HeadingsFotoemission [GND]
Emission spectroscopy [LCSH]
Scanning tunneling microscopy [LCSH]