Geometric and electronic properties of heteromolecular organic monolayers on noble metal substrates studied by photoemission spectroscopy and X-ray standing waves

The primary focus of this study was to analyze molecule-substrate and molecule-molecule interactions in heteromolecular monolayers on metallic substrates using a number of high precision experimental techniques capable of measuring the electronic and geometric properties of surfaces and ultrathin films. Therefore the first part of this works compares the geometric and electronic properties of two prototypical heteromolecular monolayer systems: CuPc+PTCDA/Ag(111) and SnPc+PTCDA/Ag(111). For one of these experimental techniques, the XSW technique, several issues were recognized that were caused by effects so far not recognized in the literature. As such, the second part of this thesis describes improved ways of analyzing NIXSW data, considering non-dipolar effects and the attenuation of the measured signal by inelastic scattering. To elaborate, in the first section, we present a systematic study of the geometric and electronic properties of hetero-organic monolayers consisting of SnPc and PTCDA adsorbed on the Ag(111) surface and we compare these properties with those of monolayers containing CuPc and PTCDA. The geometric structures of these layers has been studied with LEED, STM and the NIXSW technique, while their electronic structure has been analyzed using ARPES data that has been analyzed using the photoemission tomography technique. By comparing the two different systems, we gain insight into the in uence of the phthalocyanine central metal atom on substrate-mediated interactions in phthalocyanine-PTCDA heteromolecular monolayers. It is observed that, in particular, the PTCDA anhydride groups are very sensitive to the central metal atom of the neighboring phthalocyanines. In addition to that, considerable differences in the phthalocyanine molecules are observed as well. First of all, in both systems charge transfer takes place from the phthalocyanine fLUMO to the PTCDA fLUMO. While this transfer is complete in the case of CuPc, leading to a complete depopulation of the fLUMO, the fLUMO of SnPc is pinned to the Fermi edge instead, causing it to be partially filled. Furthermore we observe that the adsorption height of SnPc is strongly altered after mixing with PTCDA, whereas no change in adsorption height can be observed for CuPc. We show that all these differences can be traced back to differences in the interaction between the phthalocyanine central metal atom and the substrate. Based on experience obtained during these measurements, it was realized that several assumptions underpinning the NIXSW method are not valid under realistic experimental conditions and in the second section of this work we reevaluate the theory of the NIXSW method. In particular, the correction factors that are used to account for non-dipolar effects in photoelectron-monitored NIXSW measurements are affected by small yet necessary deviations from perfect normal incidence. We have shown that neglecting these effects can lead to significant deviations and therefor new equations for the calculation of these correction factors are derived and the magnitude of the deviation caused by neglecting to account for the experimental geometry is analyzed for a variety of systems. Finally, a second effect that is neglected in photoelectron-monitored NIXSW measurements is the limited mean-free path of the emitted photoelectrons. We show that under grazing emission conditions, the obtained parameters can deviate significantly from the true structural parameters and that these deviations are angle-dependent. As a result of this, angleresolved NIXSW measurements taken close to grazing conditions contain additional information about the shape of the atomic distribution function at the substrate. Two methods for analyzing angle-resolved NIXSW data are presented, one best suited for recovering the layer spacing in multilayer systems, and one method suited for obtaining information about the shape of the distribution function of poorly ordered adsorbate layers.