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: 1.93). 09/2007; 601(18):4185-4188. DOI: 10.1016/j.susc.2007.04.080


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.

4 Reads
  • [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. DOI:10.1063/1.2827864 · 2.95 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Phthalocyanines (Pcs) are capable of converting sunlight into electric energy when adsorbed on TiO2 in a dye-sensitized solar cell. Of special interest in this type of cell is the energy level alignment as well as how molecules adsorb on the surface as it determines the output of the cell. We investigated the FePc−TiO2(110) interface using scanning tunneling microscopy, synchrotron-based photoelectron spectroscopy, and X-ray absorption spectroscopy. We found a strong coupling of the first-layer FePc to the substrate resulting in an alteration of the electronic structure and charge transfer from the molecules. The FePc in the second layer is not severely affected by the bonding to the surface and has bulk-like electronic properties. The growth of FePc thin films proceeds in a layer plus island mode, and the molecular plane is parallel to the surface. The energy level alignment at the interface is determined, and the lowest unoccupied molecular orbital is found above the conduction band minimum of the oxide substrate.
    The Journal of Physical Chemistry C 03/2008; 112(15). DOI:10.1021/jp711311s · 4.77 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 · 4.77 Impact Factor
Show more