@PhdThesis{diss_mods_00022423,
  author = 	{Scheil, Katharina},
  title = 	{Scanning tunneling and atomic force microscopy of molecular switches},
  year = 	{2018},
  publisher = 	{Christian-Albrechts-Universit{\"a}t zu Kiel},
  address = 	{Kiel},
  keywords = 	{AFM; STM; molecular swiches; force spectroscopy; tunneling spectroscopy; molecular electronics},
  abstract = 	{This thesis revolves around the investigation of molecules adsorbed on metallic surfaces using combined low temperature scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The focus is on three studies addressing switching and adsorption phenomena as well as acting forces in molecular junc- tions:
Tris-[4-(phenylazo)-phenyl]-amine molecules, composed of three azobenzene subunits, are investigated on Ag(111). Controlled switching of the azobenzene subunits between two states can selectively and reversibly be achieved. It is shown that the switching process is no trans--cis isomerisation but rather a reorientation of the N--N bond of an azobenzene unit. The reorientation proceeds through a twisting motion of the azo-bridge that leads to a lateral shift of a phenyl ring.
Two cyclophane molecules with a three-dimensional double-decker structure are studied on Ag(111). The molecules are designed to attach to the surface with a naphthalene diimide subunit while either a stilbene or an azobenzene moiety is exposed to the vacuum. A striking change in corrugation and apparent height of STM images is observed at moderate bias voltages. Oval protrusions dominate the topographs at elevated voltage, but are absent at lower voltage in favor of features with submolecular dimensions. The submolecular structures are assigned to reflect the molecule's position. Calculations suggest that the oval protrusions are due to the presence of two intermolecular Ag adatoms and their electronic state.
Force spectroscopy is performed on iron tetraphenylporphyrin molecules with and without an axial Cl ligands on Au(111). The transfer of the Cl ligand between molecules and the tip of the AFM is used to systematically change the charge configuration in the junction. The maximal forces and the curve shapes considerably depend on the position and number of charged ligands in the junction. A point charge model reproduces the essential features of the force curves.},
  url = 	{https://macau.uni-kiel.de/receive/diss_mods_00022423},
  file = 	{:https://macau.uni-kiel.de/servlets/MCRFileNodeServlet/dissertation_derivate_00007488/ScheilDissertation.pdf:PDF},
  language = 	{en}
}