Elektronentransferprozesse und Funktionalisierung von Organik/Anorganik-Grenzflächen

In this thesis, the functionalization of organic/inorganic interfaces was studied. To this end, electronically induced surface reactions as well as charge transfer processes at molecular interfaces were measured and analyzed. The influence of the molecular structure of adsorbates on the products of electronically induced surface reactions was studied on datively bound diethyl ether on Si(001). Transient occupation of the LUMO and therefore the antibonding C-O σ* orbital of the molecules by tunneling electrons was found to induce ether cleavage. While thermally activated C-O dissociation is governed by strong restrictions in the transition state, the reaction products of STM tip-induced ether cleavage were significantly influenced by adsorbate-substrate interaction. In particular, the ethyl group of the final state configurations was found to predominantly form covalent bonds with Si atoms with originally unoccupied D_down states. Tip-induced ether cleavage also allows for the desorption of the ethyl group as it was split off. A comparison with tetrahydrofuran, a molecule of similar chemical composition but different spatial geometry, demonstrated that the molecular structure may determine to what extend the local electronic structure of the surface states influences the reaction process. Furthermore, tip-induced modification of surface-reacted diethyl ether on Si(001) was studied by means of STM, where covalently bound initial states were modified by a complex surface reaction. C-H dissociation in the ethyl group was induced by substrate mediated and thermally activated one electron excitation. The products of this type of surface reaction were found to form bridge-like configurations on the Si dimers. The controlled bridging of Si dimers with alkanes or other hydrocarbon chains might be considerably useful for building logical architectures on Si(001) on the molecular scale. For the investigation of charge transfer processes across organic/inorganic interfaces, experiments on copper(II) phthalocyanine on Cu(001)-2O were performed by means of time-resolved photoemission orbital tomography. Charge transfer across molecular interfaces is reflected in the population of electronic orbitals. Making use of the time-dependent evolution of the momentum distribution of the photoelectrons, unoccupied electronic states could be characterized and the temporal evolution of their distribution could be traced. It was demonstrated in a proof of principle experiment, that in the measured momentum distributions, signatures of coherent two-photon photoemission may also be observed. The separation and identification of coherent and incoherent photoemission contributions is of particular advantage when applied to organic systems as they are often characterized by many spatially localized electronic states that sometimes overlap and render the unambiguous assignment of photoemission contributions difficult. With a careful analysis of the different excitation pathways, coherent two-photon photoemission from the HOMO and photoemission from the transiently populated LUMO could be disentangled and systematically investigated in the studied system. In addition, it was demonstrated that a preferential excitation of CuPc molecules of specific orientation on the substrate could be realised by aligning the electric field of the pump pulse along the molecular axes. The insights on the functionalization of silicon surfaces with organic molecules and on optical excitation by means of time-resolved photoemission orbital tomography which were gained in this work offer possible use for future experiments on even more complex systems like organic heterostructures.