Interface formation and growth of a thin film of ZnPcCl8/Ag(111) studied by photoelectron spectroscopy

Laboratoire Matériaux et Microélectronique de Provence, UMR CNRS 6137, Faculté des Sciences de Saint Jérôme, Case 151, 13397 Marseille Cedex 20, France
Surface Science (Impact Factor: 1.87). 09/2007; 601(18):4185-4188. DOI: 10.1016/j.susc.2007.04.080

ABSTRACT We have investigated the electronic properties of a thin film of ZnPcCl8 molecules deposited on Ag(1 1 1) using ultra-violet photoelectron spectroscopy. Close to one monolayer the electronic structure differs sensibly from that of the thick film. The appearance of a density of states close to the Fermi level is interpreted as the sign of the molecule–substrate interaction via a charge transfer mechanism. An increase of the work function at the early stages of adsorption confirms that electrons are transferred from the metal to the molecular orbitals creating an interface dipole. As the coverage is increased the weak interaction between molecules of successive layers causes the electronic properties to evolve gradually towards those of the thick film. Finally, the impact of the interface electronic properties on the intermolecular interaction is discussed.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Using light-polarization-dependent angle-resolved photoemission, the metal-organic molecule bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) (or Cu(CNdpm)(2), i.e., C24H36N2O4Cu, Cu(II)) is observed to adopt a preferential orientation that depends on the film thickness and substrate when adsorbed on Co(111) and Cu(111). In addition, the final-state binding energies change with film thickness, suggesting the substrates affect the screening or charging in the photoemission final state. For Cu(CNdpm)(2) deposited on Co(111), the induced spin polarization was found to depend strongly on the molecular orbital contributions.
    The Journal of Physical Chemistry C 09/2008; 112(35):13656-13662. DOI:10.1021/jp804251b · 4.84 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The geometrical, electronic, and vibrational properties of one monolayer of Zinc-phthalocyanine (ZnPc) adsorbed on Ag(110) are studied by low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and high-resolution electron energy-loss spectroscopy (HREELS). STM and LEED revealed that the molecules lie flat on the surface, ordered in a compact arrangement with a supercell defining a coincidence mesh with the substrate lattice. By comparing the HREELS spectra of one monolayer to those of a multilayer film, in which the molecules are weakly interacting, it was found that the electronic and vibrational properties of the molecular film are sensibly perturbed at the interface. The Q and B bands corresponding to optical interband excitations measured for the multilayer are not detected for the monolayer film and an intense low-energy Drude-like plasmon loss in the infrared region is observed. The vibrational features are also modified: several Raman modes of the isolated molecule were found to become infrared active for the monolayer because of the lowering of the molecular symmetry induced by the interaction with the substrate. Moreover a sizeable vibrational softening was measured for the selected modes indicating a charge transfer from the substrate to the molecules. Finally the strong asymmetric line shape observed for one of the Raman modes is discussed in terms of interfacial dynamical charge transfer and electron-phonon coupling.
    Physical review. B, Condensed matter 06/2009; 79(23). DOI:10.1103/PhysRevB.79.235426 · 3.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The electronic structure of a thin film of chlorine-substituted Zn-phthalocyanine (ZnPcCl8) deposited on Ag(111) was studied by valence band photoemission and near-edge X-ray absorption fine structure spectroscopy. At the first stages of molecular adsorption the interface formation is accompanied by the promotion of intense interface states. A charge transfer from the substrate to lowest unoccupied molecular orbital (LUMO) of the molecules of the first layer appears as a new density of states close to the Fermi level in photoemission. The central role of the LUMO is corroborated by the reduction of the LUMO-derived transition observed in the low-coverage X-ray absorption spectrum taken at the N 1s edge. However, the lack of a sizable density of states at EF as well as the photon energy dependence of the interface state peak intensity suggest that more complicated mechanisms of intra- or extramolecular charge redistribution may also play a role. The Ag 4d-derived valence band region also appears strongly modified upon molecular adsorption. In the paper it is shown that these modifications are merely due to the vanishing of the substrate surface states and the emerging of a bulk density of states at the interface. It is suggested that such behavior should be common for other organic monolayers adsorbed on noble metal surfaces. Finally, the study of the work function as a function of coverage is presented. Its behavior is interpreted in terms of coexistence of different structural phases and compared to a local-probe work function study on the same system.
    The Journal of Physical Chemistry C 05/2008; 112(23). DOI:10.1021/jp800116j · 4.84 Impact Factor