A LEED study of NO superstructures on the Pd(111) surface

P. Kostelník1, T. Šikola1, P. Varga2, M. Schmid2

1Institute of Physical Engineering, Brno University of Technology, 61669 Brno, Czech Republic
2Institut für Allgemeine Physik, Technische Universität Wien, 1040 Wien, Austria

J. Phys. Cond. Matter 21 (2009) 134005

We have examined two adsorption structures of NO on the Pd(111) surface and the transformation between them. Low-energy electron diffraction (LEED) I(V) curves of the Pd(111)-p(2x2)-NO and Pd(111)-c(4x2)-NO surface structures were acquired and analyzed using tensor LEED. Our structural models confirm a previous study by scanning tunneling microscopy and DFT [Hansen et al., Surf. Sci. 496 (2002) 1]. In the c(4x2)-NO structure, which forms at an NO coverage of 0.5 monolayers (ML), the NO molecules occupy fcc and hcp hollow sites and are almost upright with only slight tilting, possibly related to NO-NO repulsion. In the the p(2x2)-NO structure (0.75 ML), with two NO molecules in hollow sites and one in an on-top site, we find strong tilting of the on-top molecule. Upon heating, thermal desorption of NO leads to a transition from the p(2x2) to the c(4x2) structure, which leads to splitting of the diffraction spots and/or streaky spots. The transition is discussed in terms of domain walls.

Corresponding author: M. Schmid (schmid< encoded email address >).

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