Electronic properties of Au nano-particles supported on stoichiometric and reduced TiO 2(1 1 0) substrates

Abstract

Growth modes and electronic properties were analyzed for Au nano-particles grown on stoichiometric and reduced TiO 2(1 1 0) 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 TiO 2(1 1 0) substrate. In contrast, 3D islands start to grow from initial stage with a small Au coverage (⩾0.1 ML, 1 ML = 1.39 × 10 15 atoms/cm 2: Au(1 1 1)) probably due to O-vacancies acting as a nucleation site. Above 0.7 ML, 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 ± 0.05 eV 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 TiO 2 substrate. Higher binding energy shifts of Au 4f peaks observed for both substrates reveal an electron charge transfer from Au to TiO 2 substrates. The work functions of Au nano-particles supported on the stoichiometric and reduced TiO 2 substrates were also determined as a function of Au coverage and explained clearly by the above surface and interface dipoles.