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). 01/2007; 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: Recently, we investigated the adsorption of octachloro zinc phthalocyanine (ZnPcCl(8)) on Ag(111) by scanning tunneling microscopy. Compared to the standard phthalocyanine, halogenated phthalocyanine molecules show a much more complex binding behavior, which results in the formation of three different structural phases. These phases follow from the ordering process with the formation of 8, 4 and 0 intermolecular hydrogen-halogen bonds (Abel et al 2006 ChemPhysChem 7 82). In the present work we investigate these phases by Kelvin probe force microscopy in order to quantitatively deduce the electric interface barrier of the first monolayer. Our measurements reveal that the binding behavior does not only affect the structural ordering but also the interface dipole formation, which leads to different work functions. The fact that we observe interface barriers of opposite signs between ordered and disordered molecular layers underlines the importance of exactly knowing the molecular arrangement at the interface when assembling organic molecule devices.
    Nanotechnology 07/2008; 19(30):305501. · 3.84 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 01/2009; 79(23). · 3.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Organic-metal interfaces, in particular, self-assembling systems, are interesting in the field of molecular electronics. In this study, we have investigated the formation of the Ag(110)-iron phthalocyanine (FePc) interface in a coverage range of less than 1 and up to 2 ML using synchrotron based photoelectron spectroscopy and low energy electron diffraction. As-deposited FePc forms a densely packed first layer exhibiting a 3 x 2c(6 x 2) symmetry. Upon thermal treatment the order at the interface is modified depending on the initial FePc coverage, resulting in less densely packed but still ordered superstructures. The first monolayer is relatively strongly bound to the substrate, leading to the formation of an interface state just below the Fermi level. The highest occupied molecular orbital of FePc in the second layer is found at 1 eV higher binding energy compared to the interface state.
    The Journal of Chemical Physics 03/2008; 128(6):064702. · 3.12 Impact Factor