Surface X-ray Diffraction Study of the Rh(111)+(2x2)-3CO Structure

E. Lundgren1, X. Torrelles2, J. Alvarez3, S. Ferrer3, H. Over4, A. Beutler5, J. N. Andersen5

1Institut für Allgemeine Physik, Technische Universität Wien, A-1040 Wien, Austria
2Institut de Ciencia de Materials de Barcelona (C.S.I.C), 08193 Bellaterra, Barcelona, Spain
3European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France
4Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany
5Department of Synchrotron Radiation Research, Institute of Physics, Lund University, Sölvegatan 14, S-22362 Lund, Sweden

Phys. Rev. B 59 (1999) 5876-5880

We have studied the geometry of the high coverage Rh(111)+(2x2)-3CO structure by surface x-ray diffraction. Analysis of the in-plane data set reveals three evenly separated CO molecules per (2x2) unit cell. The evaluation of the crystal truncation rods shows that one CO molecule resides in an on top site while the other two CO molecules occupy hollow sites. The intensity modulations of the out-of-plane fractional order rods provide geometrical information about distances between the C and O atoms and on the buckling of the CO overlayer.

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