Phase separation in potassium-doped ZnPc thin films

Sincrotrone Trieste S.C.p.A., Trst, Friuli Venezia Giulia, Italy
The Journal of Chemical Physics (Impact Factor: 2.95). 02/2007; 126(4):044709. DOI: 10.1063/1.2432115
Source: PubMed


In this study synchrotron radiation was used to investigate the electronic properties of a thin film of zinc-phthalocyanine (ZnPc) deposited on Si(001)-2x1 and progressively doped with K atoms. The molecular orientation was probed by angular-dependent x-ray absorption spectroscopy and the molecules were found to lie with the macrocycle plane roughly perpendicular to the surface. The evolution of the electronic properties of the film was then followed by measuring the photoemission spectra upon in situ evaporation of K atoms on the pristine ZnPc film. The results show that doping proceeds through charge donation from the K atoms to the molecular units whose lowest unoccupied molecular orbital (LUMO) becomes progressively filled. Despite the fact that the LUMO spectral weight increases as the stoichiometry x in the K(x)ZnPc compound varies from about 1 to 4 (as determined by core level photoemission), no detectable density of states was observed at the Fermi level, showing that the film remains insulating for all the investigated stoichiometries. On the other hand the C 1s spectra, which appear merely broadened at the earliest stages of doping (x approximately 1), clearly develop two distinct components when x exceeds 2, suggesting that the charge state is not the same for all the molecules. At the same time, the modification of the valence band points towards the coexistence of two distinct phases with x=2 and x=4.

Download full-text


Available from: Carla Castellarin-Cudia,
  • [Show abstract] [Hide abstract]
    ABSTRACT: The authors have studied the electronic structure of potassium doped copper-phthalocyanine using electron energy-loss spectroscopy. The evolution of the loss function indicates the formation of distinct KxCuPc phases. Taking into account the C1s and K2p core level excitations and recent results by Giovanelli et al. [J. Chem. Phys. 126, 044709 (2007)], they conclude that these are K2CuPc and K4CuPc. They discuss the changes in the electronic excitations upon doping on the basis of the molecular electronic levels and the presence of electronic correlations.
    The Journal of Chemical Physics 07/2007; 126(21):214702. DOI:10.1063/1.2741539 · 2.95 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Using first-principles calculations in the framework of density functional theory, we investigated the electronic and transport properties of metal(II)-phthalocyanine (M(II)Pc) systems, both in a single-molecule configuration and in a model device geometry. In particular, using copper(II)-Pc and manganese(II)-Pc as prototypical examples, we studied how electronic correlations on the central metal ion influence the analysis of the electronic structure of the system and we demonstrated that the choice of the exchange-correlation functional, also beyond the standard local or gradient corrected level, is of crucial importance for a correct interpretation of the data. Finally, our electronic transport simulations have shown that M(II)Pc-based devices can act selectively as molecular conductors, as in the case of copper, or as spin valves, as in the case of manganese, demonstrating once more the great potential of these systems for molecular nanoelectronics applications.
    Nanotechnology 10/2007; 18(42):424013. DOI:10.1088/0957-4484/18/42/424013 · 3.82 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the effect that potassium intercalation has on the electronic structure of copper phthalocyanine (CuPc) molecular crystals by means of ab initio density functional calculations. Pristine CuPc (in its alpha and beta structures) is found to be an insulator containing local magnetic moments due to the partially filled Cud shells of the molecules. The valence band is built out of molecular Pc-ring states with eg symmetry and has a width of 0.38/0.32eV in the alpha/beta polymorph. When intercalated to form K2CuPc , two electrons are added to the Pc-ring states of each molecule. A molecular low spin state results, preserving the local magnetic moment on the copper ions. The degeneracy of the molecular eg levels is lifted by a crystal field, resulting in a splitting of 52meV between occupied and empty bands. Electronic correlation effects enhance the charge gap of K2CuPc far beyond this splitting; it is 1.4eV . The conduction band width is 0.56eV , which is surprisingly large for a molecular solid. This finding is in line with the observed metallicity of K2.75CuPc , indicating that in this compound the large bandwidth combined with a substantial carrier concentration prevents polaron localization.
    Physical review. B, Condensed matter 01/2008; 77(3). DOI:10.1103/PhysRevB.77.035133 · 3.66 Impact Factor
Show more