The interaction of pentacene molecules in contact with the Cu(119) stepped surface has been directly imaged by scanning tunneling microscopy and analyzed by angle resolved photoemission spectroscopy. Interacting molecules, which are in contact with copper, generate dispersive electronic states associated with a perturbed electron charge density distribution of the molecular orbitals. In contrast, the electron charge density of molecules of the pentacene on top of the first layer, which is not in direct contact with the Cu surface, shows an intramolecular structure very similar to that of the free molecule. Our results indicate that the delocalization of the molecular states in the pentacene/Cu system is confined to the very first molecular layer at the interface.

The discontinuity in the lattice periodic potential at surfaces often leads to the creation of new electronic surface states. We developed a photoemission based Fermi surface tomography whose surface sensitivity allowed us to quantify the charge redistribution on the Be(0001) surface. The volume enclosed by the bulklike Fermi surface is significantly reduced at the surface, consistent with the charge transfer to the two surface states as estimated from the area within their two-dimensional Fermi contours. This result represents the first quantification of the charge redistribution on a natural surface termination.

When mapping spatially resolved photoemission intensity for electron kinetic energy corresponding to Fermi energy, one obtains a spherical cut through a three-dimensional Fermi surface of a metal. At the APE-INFM beamline at Elettra, we developed an automated method of measuring the Fermi surface cuts for a large number of photon energies and putting them together in order to reconstruct the three-dimensional Fermi surface. The energy and k∥ (momentum parallel to the surface) resolution are set by the monochromator and energy analyzer properties, while the k⊥ (momentum perpendicular to the surface) resolution depends on the photon energy step chosen for obtaining subsequent data sets. By 3D interpolation of the data, one obtains the k-space tomography of the constant initial state surfaces (e.g. of the Fermi surface). From the tomography, one can retrieve true kx, ky, kz resolved maps. Besides de Haas van Alphen (dHvA) oscillations, this method is the most direct way for the determination of the Fermi surfaces. A set of data on the Fermi surface of Be(0001) is presented and compared to dHvA data and theory.

We have investigated the structural and electronic properties of a pentacene film (∼2nm) grown on the Cu(119) substrate using scanning tunneling microscopy (STM) and synchrotron based angle-resolved UV photoelectron spectroscopy at room temperature. STM images indicate an ordered superstructure of pentacene molecules lying almost flat with respect to the substrate. From angular-resolved photoemission spectra, we have observed an energy-band dispersion of about 100meV for the highest occupied molecular orbital in the direction perpendicular to the pentacene surface.

The self organization of pentacene to form ordered film structures can be driven by the large structural anisotropy of suitable metal substrates [1]. We have prepared and studied pentacene films as grown on Cu(119) (Cu(100) vicinal surface with terrace width ~1,15 nm) with a surface science approach, i.e by LEED, STM, STS and ARPES measurements with polarized synchrotron radiation. These films show a long-range ordered structure, with the long molecular axis aligned along the step direction of the substrate. The formation of a single layer of pentacene molecules on the substrate kept at 373 K, results in longrange-ordered chain structures, as observed in STM images and in the 3 x 7 reconstruction observed by LEED. The character of the interface and molecular states was investigated by measuring ARPES in different experimental geometries, e.g. using linearly polarized synchrotron radiation oriented parallel or perpendicular to the steps of the vicinal surface (i.e. parallel or perpendicular to the longer molecular axis). As the thickness of the film increases, the intermolecular forces start to play a more important role than interface interaction in determining the relative orientation of the molecules and the electronic properties of the film. In a pentacene multilayer ~2nm thick the orientation of the molecules was observed by STM, which shows still an ordered array of the molecules lying almost flat on the surface. The extent of the intermolecular interaction was evaluated from the ARUPS measurements by looking at the energy dispersion of HOMO band along the molecular plane normal.