Adsorption of CO on Cs-precovered Ru(001): formation of a double-layer structure Cs Cs + CO Ru and complete screening of the CO dipole

H. Kondoh, H. Nozoye

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Adsorption of CO on Cs-precovered Ru(001) with one-monolayer coverage (θCs = 0.33) has been investigated by means of electron energy loss spectroscopy (EELS), temperature-programmed desorption (TPD), low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). We found unusual adsorption of CO on the Cs(1 ML) Ru(001) surface. Gaseous CO adsorbs on the completely Cs-precovered surface at 85 K to a saturation coverage of 0.23. Although the low-resolution EELS and UPS results indicate that CO molecularly adsorbs on this surface, the CO stretching mode is not observed in the specular mode of high-resolution EELS but clearly appears at quite a low frequency of 1245 cm-1 in the off-specular mode. From a combination of the EELS, TPD and XPS experiments, we propose an adsorption model in which the CO molecules displace one-fourth of the Cs adatoms from the preadsorbed Cs monolayer, resulting in formation of a double-layer structure, Cs Cs + CO Ru(001); the displaced Cs atoms adsorb on the "rotated-p(2 × 2)" lattice which is composed of Cs and CO with a ratio of 1 : 1. In this adsorption state, it is considered that the CO species has an inclined or a side-on-bonded geometry and that the CO dipole is effectively screened by the second-layer Cs. This complete screening of the CO dipole is explained in terms of combined effects of the embedding of CO into the double-layer structure, a large polarizability of Cs and laterally delocalized electrons in the double-layer structure.

Original languageEnglish
Pages (from-to)39-54
Number of pages16
JournalSurface Science
Issue number1-3
Publication statusPublished - 1995 Jul 10
Externally publishedYes


  • Alkali metals
  • Carbon monoxide
  • Chemisorption
  • Electron energy loss spectroscopy
  • Low-energy electron diffraction (LEED)
  • Ruthenium
  • Surface relaxation and reconstruction Thermal desorption spectroscopy
  • Vibrations of adsorbed molecules
  • Visible and ultraviolet photoelectron spectroscopy
  • X-ray photoelectron spectroscopy

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry


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