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The valence and conduction bands of a thin film of tetra(4-aminophenyl)porphyrin (TAPP) are investigated by direct and inverse photoemission as well as by comparison to density functional theory (DFT) calculations. By projecting the electronic eigenfunctions onto the molecular framework it was possible to interpret the origin of each spectroscopic feature. Although the majority of the photoemission spectrum is attributed to the unsubstituted tetraphenylporphyrin (TPP) parent molecule, several features are clearly due to the amino substitution. Substitution also has important consequences for the energy positions of the frontier orbitals and therefore on the low-energy electronic excitations. The measured electronic transport energy gap ( E g = 1.85 eV) between the highest occupied molecular orbital (HOMO) and lowest unoccupied (LUMO) in TAPP is found to be significantly reduced with respect to TPP. Moreover, an increased energy separation between the two highest occupied states (HOMO and HOMO−1) is found both experimentally and by DFT calculations. Such evidence is attributed to an increased HOMO orbital destabilization due to an enhanced electron-donor character of the phenyl substituents upon amino functionalization. Finally, the above findings together with further time-dependent DFT calculations are used to interpret the effect of the amino groups on the UV–Vis absorption spectrum, namely an overall red-shift of the spectrum and remarkable intensity changes within the Q band. [ABSTRACT FROM AUTHOR]

Adsorption of organic molecules on well-oriented single-crystal coinage metal surfaces fundamentally affects the energy distribution curve of ultraviolet photoelectron spectroscopy spectra. New features not present in the spectrum of the pristine metal can be assigned as "interface states" having some degree of molecule-substrate hybridization. Here it is shown that interface states having molecular orbital character can easily be identified at low binding energy as isolated features above the featureless substrate sp plateau. On the other hand, much care must be taken in assigning adsorbate-induced features when these lie within the d-band spectral region of the substrate. In fact, features often interpreted as characteristic of the molecule-substrate interaction may actually arise from substrate photoclectrons scattered by the adsorbates. This phenomenon is illustrated through a series of examples of noble-metal single-crystal surfaces covered by monolayers of large π-conjugated organic molecules. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated the electronic properties of a thin film of ZnPcCl8 molecules deposited on Ag(111) 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. [Copyright &y& Elsevier]

Abstract: Atomically thin Co/Pt(111) interfaces grown at different temperatures are characterized by very different values of perpendicular magnetic anisotropy as a consequence of the local structure and coordination. Here we present a study of the structural, magnetic and electronic properties for interfaces grown in UHV onto clean Pt(111) in different kinetic conditions. When one monolayer of Co is deposited at 540K a thermally activated exchange reaction leads to a sharp Pt–Co double interface giving rise to a strong increase of the magneto-optical response with respect to the Co monolayer deposited at room temperature. The results are interpreted in terms of atomic hybridization as detected by valence band photoelectron spectroscopy. [Copyright &y& Elsevier]

The surface properties of SnO2(1 1 0)-4×1 and sputtered SnO2(1 1 0) were studied comparatively by resonant photoemission of the valence band states in a photon energy range of 60–130 eV. Resonating energetic levels could be observed on the 4×1 reconstructed surface and the resonance behavior could be switched off by sputter treatment. Additionally, the Sn 4d core-levels were recorded at two photon energies in order to allow a statement about the surface''s stoichiometry. A tentative explanation of the observed resonance and of the discrepancy between ordered and sputtered surface is given with regard to recent STM results on similar prepared surfaces. [Copyright &y& Elsevier]