Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 32: Oxides and Insulators: Clean Surfaces

O 32.8: Vortrag

Dienstag, 26. Februar 2008, 14:45–15:00, MA 042

Work function measurements with a combined AFM/STM setup under ultrahigh vacuum conditions at 5K on thin MgO films grown on Ag(001) — •Thomas König, Georg Hermann Simon, Violeta Simic-Milosevic, Markus Heyde, and Hans-Joachim Freund — Fritz-Haber-Institute of the Max-Planck-Society, Faradayweg 4-6, 14196 Berlin, Germany

For many years metal supported thin oxide films have been investigated in the research field of heterogeneous catalysis. The properties of the thin films depend strongly on both the support and the film thickness. While thick films approach the properties of bulk material thin films exhibit their own characteristics. It has been proposed by Pacchioni et al. [1] that charging can occur by depositing metal atoms on ultrathin MgO films grown on metal supports. The charging of Au atoms on top of a thin MgO film grown on Ag(001) has been confirmed by STM measurements done by Sterrer et al. [2]. The MgO film on top the metal support leads to a compression of the metal electrons which for a free metal spill over into the vacuum. The compression results in a reduction of the surface dipole and thus to a decrease of the work function. Here we present work function measurements on different MgO film thicknesses grown on Ag(001). The measurements have been done with our combined AFM/STM setup operating under UHV conditions at 5K. The results will be discussed and compared with theoretical calculations.

[1] L. G. Giordano et al., Phys. Rev. B 73, 045414, 2005. [2] M. Sterrer et al., Phys. Rev. Lett. 98, 096107, 2007.