Metal-Phthalocyanines on Noble Metal Surfaces: Charge Transfer, Bonding and Kondo Effect

Wednesday, 20 April 2016, at 11:15 in Y36 J33

Metal-organic interfaces provide an interesting playground to study fundamental physical effects such as interaction mechanisms and their influence on the electronic structure.
In case of particular adsorbate/substrate combinations the lowest unoccupied molecular orbital (LUMO) is (partially) occupied due to hybridization with and charge transfer from the metal substrate. For iron phthalocyanine (FePc) on Ag(110), the LUMO, which is two-fold degenerate in the gas phase, is pulled well below the Fermi level and an energetic splitting of 230 meV can be observed in high-resolution photoelectron spectroscopy (PES). The two LUMO components can be identified due to their characteristic signatures in k-space. This lift of degeneracy is explained by a reduction of the four-fold symmetry of the gas phase molecule upon adsorption on the two-fold symmetric substrate.
In case of a partial filling of the LUMO, a Kondo effect can be observed, which manifests itself by a very narrow feature at the Fermi energy. At low temperatures (T < 20K), the line-width of this feature amounts to only ~ 10 meV, representing an unusually small energy scale for electronic excitations in these systems . This occurs e.g. for copper phthalocyanine (CuPc) on Ag(100), where the analysis of the k-space intensity patterns indicates that only one of the degenerate LUMOs receives charge transfer.