Localized and dispersive electronic states at ordered FePc and CoPc chains on Au(110)

Iron and cobalt phthalocyanines assemble on the Au(110) surface lying parallel to the surface, as deduced by near-edge X-ray absorption fine structure (NEXAFS) taken with linearly polarized radiation at the C and N K edges. The molecular chains, firmly anchored to the underlying metal surface, arrange into long-range ordered rows with a (5 x 3) symmetry along the [001] azimuthal direction at completion of the first single layer. The interaction process is mainly determined by the d orbitals associated with the central Fe and Co atoms, as observed by valence band photoemission and NEXAFS at the Fe and Co L(2,3) edges. The spin and orbital configuration of the Fe Pc and Co Pc molecules is strongly influenced by the interface with a charge transfer from the underlying metal to the out-of-plane empty states located at the Fe and Co centers of the molecules. This interaction process induces electronic states located at the interface, localized on the central metal atoms and close to the Fermi level (0.2 eV binding energy for Fe Pc and 0.7 eV for Co Pc) without energy dispersion, as deduced by angular-resolved photoemission. On the contrary, a delocalized state has been observed with dispersion along the molecular chains, mainly due to the overlapping of the pi charge of the macrocycles ligands mediated by the Au substrate.