Localized and Dispersive Electronic States at Ordered FePc and CoPc Chains on Au(110) Maria Grazia Betti,* ,† Pierluigi Gargiani, † Riccardo Frisenda, † Roberto Biagi, ‡ Albano Cossaro, § Alberto Verdini, § Luca Floreano, § and Carlo Mariani † Dipartimento di Fisica, UniVersita ` di Roma “La Sapienza”, Piazzale A. Moro 5, I-00185 Roma, Italy, Dipartimento di Fisica, UniVersita ` di Modena e Reggio Emilia, Via G. Campi 213/A, I-41100 Modena, Italy, and CNR-IOM, Laboratorio Nazionale TASC, BasoVizza SS-14, Km 163.5, I-34012 Trieste, Italy ReceiVed: September 13, 2010; ReVised Manuscript ReceiVed: October 19, 2010 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 × 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 FePc and CoPc 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 FePc and 0.7 eV for CoPc) 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 π charge of the macrocycles ligands mediated by the Au substrate. Introduction Molecular self-assembly at surfaces is a convenient process for tailoring the functions of organic nanostructures by control- ling the properties of the individual molecular building blocks. Molecular building blocks can be combined into desired functional architectures at suitable templates. This variety of molecular superstructures displays a rich selection of intriguing functional properties, which one may exploit in magnetic, optical, and electronic devices. 1,2 The actual feasibility of these construction strategies has already been demonstrated for several applications ranging from spintronics 3 to molecular recognition 4 and from biomimetic applications 5 to catalysis. 4 Regular patterns of metallorganic molecules at surfaces can ensure formation of a regular grid of metal atoms surrounded by macrocycle ligands, allowing for tunable anchoring sites, molecular orientation, and interaction strength. Organometallic molecules like metal-phthalocyanines (M-C 32 H 16 N 8 , MPc) are archetypal metallorganic complexes constituted by four pyrrolic and four benzene rings arranged around the central metal atom. These stable aromatic dyes have a 2-fold interest: the π conjugation guarantees charge delocalization and electron mobility, and the central metal atom plays a crucial role to determine the electronic/magnetic properties. 1,2 Furthermore, the unique flexibility of MPcs in coordinating more than 70 elemental ions and the tendency to self-assemble on metal surfaces forming ordered aggregates or films make MPcs suitable systems to control and manipulate the electronic and magnetic properties of desired organic nanostructures at surfaces. The final aim is controlling the functions of these ordered molecular structures and the degree of charge delocalization. This goal is strictly related to the control of the interaction strength of the macrocycles and of the central metal atoms with the underlying substrate. 6-10 If the charge located on the macrocycles and/or on the central metal atoms is delocalized, it should be revealed by an electronic band dispersion. Generally, π-conjugated molecules deposited on metal substrates adsorb in a planar configuration, so far only limited experimental results have been collected on the intermolecular dispersion of elec- tronic states of molecular single layers 11-15 or multilayers. 16-19 In particular, copper-phthalocyanine deposited on the Au(110) surface forms ordered chains along the Au reconstructed channels, giving rise to a delocalized quasi-1D band dispersive along the chains, 12 probably due the overlapping of the macrocycle states mediated by the gold substrate. Our purpose is to identify the origin and nature of the electron states located at the interface for the ordered FePc and CoPc molecular structures deposited on the Au(110) surface, to control the role of the macrocycle ligands and the central metal atoms in the interaction process, and to verify the degree of delocalization by controlling the band dispersion. Experimental Section Photoemission experiments have been carried out at the surface physics laboratory LOTUS at the Universita “La Sapienza” in Roma; NEXAFS experiments have been performed at the ALOISA beamline of the Elettra synchrotron radiation facility, in ultrahigh-vacuum (UHV) systems with base pressures better than 1 × 10 -10 mbar. Both laboratories are equipped with analogous ancillary facilities for sample preparation and mo- lecular deposition and control. Surface quality and cleanness were checked by means of low-energy electron-diffraction * To whom correspondence should be addressed. E-mail: maria.grazia. betti@roma1.infn.it. † Universita ` di Roma “La Sapienza”. ‡ Universita ` di Modena e Reggio Emilia. § Laboratorio Nazionale TASC. J. Phys. Chem. C 2010, 114, 21638–21644 21638 10.1021/jp108734u  2010 American Chemical Society Published on Web 11/16/2010