Abstract
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 language | English |
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Pages (from-to) | 39-54 |
Number of pages | 16 |
Journal | Surface Science |
Volume | 334 |
Issue number | 1-3 |
DOIs | |
Publication status | Published - 1995 Jul 10 |
Externally published | Yes |
Keywords
- 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