Experimental and Theoretical Scanning Tunneling Spectroscopy Analysis of an Ultrathin Titania Film and Adsorbed Au Nanoparticles

We present a detailed experimental and theoretical investigation of the ultrathin titania z'-TiOx/Pt(111) phase and Au nanoparticles assembled on it. Scanning tunneling spectroscopy (STS) at two different tip stabilization biases (TSB) is measured at three different locations on the bare titania phase and on top of the Au nanoparticles (NPs). STS data are compared with the results of first-principles calculations based on a Tersoff-Hamann approach for simulating tunneling currents. We obtain a coherent framework in which STS features can be used as fingerprints with atomistic resolution of the local density of states. On the bare titania, Shockley states coming from the 0 atoms dominate the occupied DOS, while resonant states coming from the Ti atoms dominate the DOS above the Fermi level. The ultrathin film is partially metallized, with DOS empty channels at the hole sites, hence lying in an intermediate state between a semiconducting oxide and a conductor. Finally, STS data on top of Au nanoparticles provide information on the coordination environment of the Au atom in direct contact with the titania phase, discriminating between the Au metallic or nonmetallic regime.