The electronic structure of a vapor-sublimated thin film of metal-free phthalocyanine (H2Pc) is studied experimentally and theoretically. An atom-specific picture of the occupied and unoccupied electronic states is obtained using x-ray-absorption spectroscopy (XAS), core- and valence-level x-ray photoelectron spectroscopy (XPS), and density-functional theory (DFT) calculations. The DFT calculations allow for an identification of the contributions from individual nitrogen atoms to the experimental N1s XAS and valence XPS spectra. This comprehensive study of metal-free phthalocyanine is relevant for the application of such molecules in molecular electronics and provides a solid foundation for identifying modifications in the electronic structure induced by various substituent groups.

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The initial stages of TiO2 growth on Si(111) under ultra-high vacuum conditions is studied using core level photoelectron spectroscopy, x-ray absorption spectroscopy, and scanning tunneling microscopy. The TiO2 film was formed by means of chemical vapor deposition of titanium(IV) isopropoxide at a sample temperature of 500 °C. The thickness and composition of the amorphous interface layer and its subsequent transition to crystalline anatase TiO2 are discussed. Three different stages are identified: In the initial stage (film thickness <10 Å), the oxygen atoms are coordinated mainly to Si atoms giving rise to Ti atoms with oxidation states lower than 4+. At this stage, a small amount of carbon (0.15 ML) is observed. The next stage (<25 Å) is best described as an amorphous TiSixOy compound in which the oxidation state of Ti is 4+ and the x and y values vary monotonically with the film thickness, from 2 to 0 and 4 to 2, respectively. Finally (>30 Å) a stoichiometric TiO2 layer starts to form. The TiO2 phase is anatase and the layer consists of particles ∼10 nm wide.

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