Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 51: Surface chemical reactions I

O 51.9: Vortrag

Donnerstag, 26. März 2009, 18:15–18:30, SCH A01

HREELS study of Cu clusters deposited on the O-terminated ZnO(000-1) surface — •Hengshan Qiu, Yuemin Wang, and Christof Wöll — Physical Chemistry I, Ruhr-University Bochum, 44780 Bochum, Germany

The interaction of metal clusters and films with oxide substrates plays a key roleas regards the microscopic mechanisms of many processes in heterogeneous ctatalysis. In this work, the interaction of Cu clusters with the O-terminated ZnO(000-1) surface was studied by high-resolution energy loss spectroscopy (HREELS),together with thermal desorption spectroscopy (TDS) and low-energy electron diffraction (LEED). It was found that Cu deposition on O-ZnO leads to the formation of well-defined islands with the Cu(111) facets. For the small clusters the partial oxidation of Cu0 into Cu+ was clearly identified by the characteristic changes in the C-O stretch frequencies of CO molecules adsorbed on the Cu atoms. Upon heating the Cu atoms undergo, instead of desorption, diffusion into the O-ZnO bulk. The doping of ZnO by Cu leads to the formation of shallow donor states, in which the electrons can be thermally excited into the conduction band and, as a result, give rise to the plasmon-induced broadening of the quasielastic peak in HREELS [1]. From the observed temperature dependence, the donor level ionization energy was determined. This unexpected doping effect of ZnO by Cu has important consequences for its chemical activity, as confirmed by detailed studies on CO2 adsorption. [1]H. Qiu, B. Meyer, Y. Wang, Ch. Wöll, Phys. Rev. Lett. in press (2008).