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Abstract: Growth modes and electronic properties were analyzed for Au nano-particles grown on stoichiometric and reduced TiO2(110) substrates by medium energy ion scattering (MEIS) and photoelectron spectroscopy(PES) using synchrotron-radiation-light. Initially, two-dimensional islands (2D) with a height of one and two atomic layers grow and higher coverage increases the islands height to form three-dimensional (3D) islands for the stoichiometric TiO2(110) substrate. In contrast, 3D islands start to grow from initial stage with a small Au coverage (⩾0.1ML, 1ML=1.39×1015 atoms/cm2: Au(111)) probably due to O-vacancies acting as a nucleation site. Above 0.7ML, all the islands become 3D ones taking a shape of a partial sphere and the Au clusters change to metal for both substrates. We observed the Au 4f and Ti 3p core level shifts together with the valence band spectra. The Ti 3p peak for the O-deficient surface shifts to higher binding energy by 0.25±0.05eV compared to that for the stoichiometric surface, indicating downward band bending by an electron charge transfer from an O-vacancy induced surface state band to n-type TiO2 substrate. Higher binding energy shifts of Au 4f peaks observed for both substrates reveal an electron charge transfer from Au to TiO2 substrates. The work functions of Au nano-particles supported on the stoichiometric and reduced TiO2 substrates were also determined as a function of Au coverage and explained clearly by the above surface and interface dipoles. [Copyright &y& Elsevier]

Abstract: The growth mode and electronic structure of Au nano-clusters grown on NiO and TiO2 were analyzed by reflection high-energy electron diffraction, a field-emission type scanning electron microscope, medium energy ion scattering and photoelectron spectroscopy. Au was deposited on clean NiO(001)-1×1 and TiO2(110)-1×1 surfaces at room temperature with a Knudsen cell at a rate of 0.25–0.35ML/min (1ML=1.39×1015 atoms/cm2:Au(111)). Initially two-dimensional (2D) islands with thickness of one Au-atom layer grow epitaxially on NiO(001) and then neighboring 2D-islands link each other to form three-dimensional (3D)-islands with the c-axis oriented to the [111] direction. The critical size to form 3D-islands is estimated to be about 5nm2. The shape of the 3D-islands is well approximated by a partial sphere with a diameter d and height h ranging from 2.0 to 11.8nm and from 0.95 to 4.2nm, respectively for Au coverage from 0.13 to 4.6ML. The valence band spectra show that the Au/NiO and Au/TiO2 surfaces have metallic characters for Au coverage above 0.9ML. We observed Au 4f spectra and found no binding energy shift for Au/NiO but significant higher binding energy shifts for Au/TiO2 due to an electron charge transfer from Au to TiO2. The work function of Au/NiO(001) gradually increases with increase in Au coverage from 4.4eV (NiO(001)) to 5.36eV (Au(111)). In contrast, a small Au deposition(0.15 to 1.5ML) on TiO2(110) leads to reduction of the work function, which is correlated with an electron charge transfer from Au to TiO2 substrate. [Copyright &y& Elsevier]