We investigated the growth of titanium oxide two-dimensional (2D) nanostructures on Au(111), produced by Ti evaporation and post-deposition oxidation. Scanning tunneling microscopy and spectroscopy (STM and STS) and low-energy electron diffraction (LEED) measurements characterized the morphological, structural and electronic properties of the observed structures. Five distinct TiOx phases were identified: the honeycomb and pinwheel phases appear as monolayer films wetting the gold surface, while nanocrystallites of the triangular, row and needle phases grow mainly over the honeycomb or pinwheel layers. Density Functional Theory (DFT) investigation of the honeycomb structure supports a (2 × 2) structural model based on a Ti-O bilayer having Ti2O3 stoichiometry. The pinwheel phase was observed to evolve, for increasing coverage, from single triangular crystallites to a well-ordered film forming a (4 √ 7 × 4 √ 7)R19.1• superstructure, which can be interpreted within a moiré-like model. Structural characteristics of the other three phases were disclosed from the analysis of high-resolution STM measurements. STS measurements revealed a partial metallization of honeycomb and pinwheel and a semiconducting character of row and triangular phases.

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The adsorption of Zn-Tetra-Phenyl-Porphyrin (ZnTPP) on nanoporous hierarchically organized anatase TiO 2 structures, and the properties of the corresponding hybrid interface were studied by synchrotron radiation experiments. The molecular structure, electronic properties and the bonding with nanostructured TiO 2 surfaces were analyzed by photoemission (XPS and UPS) and x-ray absorption spectroscopy (XAS). The charge transfer at the interface was investigated by means of valence band resonant photoemission experiments (ResPES) at the C K edge. We show that the charge transfer dynamics between the photo-excited ZnTPP and TiO 2 is strongly influenced by the presence of defects on the TiO 2 surface. On a stoichiometric anatase nanostructure, ZnTPP bonding occurs primarily via carbon atoms belonging to the molecular phenyl rings and this creates a preferential channel for the charge transfer. This phenomenon is reduced in the case of defective TiO 2 surface, where ZnTPP interacts mainly through the molecule macrocycle. Our results represent a surface science study of the dye molecule behavior on a nanoporous TiO 2 photoanode relevant to dye-sensitized or hybrid solar cell applications and it shows the importance of the surface oxidation state for the charge transfer process.

We present a method for the preparation of bulk molybdenum tips for Scanning Tunneling Microscopy and Spectroscopy and we assess their potential in performing high resolution imaging and local spectroscopy by measurements on different single crystal surfaces in UHV, namely, Au(111), Si(111)-7 × 7, and titanium oxide 2D ordered nanostructures supported on Au(111). The fabrication method is versatile and can be extended to other metals, e.g., cobalt.