title: Coverage-dependent adsorption geometry of octithiophene on Au(111).
abstract: The adsorption behavior of α-octithiophene (8T) on the Au(111) surface as a function of 8T coverage has been studied with low-temperature scanning tunneling microscopy, high resolution electron energy loss spectroscopy as well as with angle-resolved two-photon photoemission and ultraviolet photoemission spectroscopy. In the sub-monolayer regime 8T adopts a flat-lying adsorption geometry. Upon reaching the monolayer coverage the orientation of 8T molecules changes towards a tilted configuration, with the long molecular axis parallel to the surface plane, facilitating attractive intermolecular π-π-interactions. The photoemission intensity from the highest occupied molecular orbitals (HOMO and HOMO - 1) possesses a strong dependence on the adsorption geometry due to the direction of the involved transition dipole moment for the respective photoemission process. The change in molecular orientation as a function of coverage in the first molecular layer mirrors the delicate balance between intermolecular and molecule/substrate interactions. Fine tuning of these interactions opens up the possibility to control the molecular structure and accordingly the desirable functionality.
authors.affiliation: Freie Universität Berlin, Fachbereich Physik, Berlin, Germany.
authors.forename: Erwan
authors.initials: E
authors.lastname: Varene
authors.forename: Lea
authors.initials: L
authors.lastname: Bogner
authors.forename: Stephan
authors.initials: S
authors.lastname: Meyer
authors.forename: Yan
authors.initials: Y
authors.lastname: Pennec
authors.forename: Petra
authors.initials: P
authors.lastname: Tegeder