Our group investigates many aspects of the adsorption of organic molecules on different surfaces like transition metals and graphene. Particular attention is being paid to the electronic as well as the structural properties of the molecular layers. Especially the interplay of the intermolecular and molecule/substrate interactions is investigated with a plentitude of experimental techniques like photoelectron spectroscopy (PES), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and synchrotron based techniques.
For a number of different adsorbate/surface systems we could show that a sophisticated interplay of intermolecular and molecules/substrate interaction steers the molecular self-assembly as well as the interface structure. E. g. for the adsorption of 6-mercaptopurine (a molecule relevant for treatment of some leukemia and autoimmune conditions) on reconstructed Au(100) we could show that the hexagonal surface reconstruction was lifted by adsorption of the organic molecule although two different adsorption structures were present on the surface. (Carro 2017) In contrast adsorption of a triarylamines-derivative functionalized with three cyano groups does not modify the Au(111) herringbone reconstruction but leads to a slight displacement of the Au atoms underneath the cyano groups. (Müller 2016)
Besides the adsorption of organic molecules on metal surfaces our group also investigates the adsorption of molecules on graphene. Especially the possibility of steering the doping of the graphene by varying the amount of molecular adsorbates or specific organic synthesis is considered a valuable step towards specific design of graphene’s electronic properties. For example charge neutrality of monolayer graphene on SiC can be reached by the adsorption of a full layer of tetrafluorotetracyanoquinodimethane. (Coletti 2010)
- K. Müller, N. Schmidt, S. Link, R. Riedel, H. Bock, W. Malone, K. Lasri, A. Kara, U. Starke, M. Kivala, M. Stöhr, Small 15, 1901741 (2019). Triphenylene-Derived Electron Acceptors and Donors on Ag(111): Formation of Intermolecular Charge-Transfer Complexes with Common Unoccupied Molecular States.
- P. Carro, K. Müller, F. Lobo Maza, C. Vericat, U. Starke, K. Kern, R.C. Salvarezza, and D. Grumelli, J. Phys. Chem. C 121, 8938-8943 (2017). 6-Mercaptopurine Self-Assembled Monolayers on Gold (001)-Hex: Revealing the Fate of Gold Adatoms.
- C. Morchutt, J. Björk, C. Straßer, U. Starke, R. Gutzler, and K. Kern, ACS Nano 10, 11511-11518 (2016). Interplay of Chemical and Electronic Structure on the Single-Molecule Level in 2D Polymerization.
- K. Müller, M. Enache and M. Stöhr, J. Phys.: Condens. Matter 28, 153003 (2016). Confinement properties of 2D porous molecular networks on metal surfaces.
- K. Müller, J.C. Moreno-López, S. Gottardi, U. Meinhardt, H. Yildirim, A. Kara, M. Kivala, and M. Stöhr, Chemistry A European Journal 22, 581-589 (2016). Cyano-functionalized triarylamines on coinage metal surfaces: interplay of intermolecular and molecule-substrate interactions.
- C. Coletti, C. Riedl, D.S. Lee, B. Krauss, L. Patthey, K.v. Klitzing, J.H. Smet, and U. Starke, Phys. Rev. B 81, 235401 (2010), Band structure engineering of epitaxial graphene on SiC by molecular doping.