Dresden 2011 – scientific programme

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O: Fachverband Oberflächenphysik

O 99: Electron and spin dynamics II

O 99.5: Talk

Friday, March 18, 2011, 12:15–12:30, WIL B321

Two-photon photoemission study of ultrathin NiO(100) films on Ag(001) — •Mario Kiel, Klaus Duncker, Stephan Grosser, and Wolf Widdra — Martin-Luther-Universität Halle-Wittenberg, Halle, Germany

The electron dynamics within ultrathin transition metal oxide NiO films grown on a Ag(001) substrate have been investigated using time-resolved two-photon photoemission (2PPE) in combination with scanning tunneling microscopy and spectroscopy (STM, STS).

For sub-monolayer NiO coverages upward shifts of the well-known Ag(001) image potential states are observed. These are explained by the increase of the electrostatic potential close to the surface due to the local work function difference between Ag(001) and NiO islands.

Using two-color 2PPE an unoccupied Ni 3d state at 3.73 eV above the Fermi energy is identified for the NiO monolayer. This Ni 3d state is also observed as prominent feature in STS spectra for defect-free NiO monolayer islands. Time-resolved data reveal a short lifetime of approx. 35 fs for this state. Additionally a second unoccupied Ni 3d-derived state at 2.4 eV is identified in 2PPE as well as in STS spectra.