Adsorbate{endash}adsorbate repulsions{emdash}the coverage dependence of the adsorption structure of CO on Cu(110) as studied by electron-stimulated desorption ion angular distribution
- Department of Chemistry, University of Pittsburgh, Surface Science Center, Pittsburgh, Pennsylvania 15260 (United States)
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)
The coverage dependent orientation of CO adsorbed on a Cu(110) surface was studied by the electron-stimulated desorption ion angular distribution (ESDIAD) technique. A neutral excited (CO{asterisk}) species is imaged and in addition positive ions are measured. The adsorption temperature was varied between 32 K and 150 K. By applying the ESDIAD technique at a temperature below 80 K it was possible to decrease the beamwidths drastically, to determine the angular distributions better than {plus_minus}0.5{degree}, and to study the adsorption of CO chemisorbed and physisorbed on the surface. With increasing CO coverage we observe three distinct ESDIAD patterns. Starting from a normal beam pattern with an elliptical cross section with the major axis oriented in the {l_angle}1{bar 1}0{r_angle} direction for coverages up to 0.2 monolayer (ML), a transformation of the ESDIAD pattern into a pattern of two separated beams is observed for a coverage of about 0.5 ML, indicating a tilting of the molecules in the {l_angle}1{bar 1}0{r_angle} directions by {approximately}9{degree}. With further increasing CO coverage an additional central peak develops with an elliptical broadening now in the {l_angle}001{r_angle} direction. The changes of the pattern are reversible as shown by decreasing the coverage by thermal desorption. Based on these ESDIAD and digital low energy electron diffraction results, a linear-chain model for CO adsorption is proposed. Temperature programmed desorption measurements also indicate the presence of repulsive CO{endash}CO interactions in the adlayer. {copyright} {ital 1996 American Institute of Physics.}
- OSTI ID:
- 385647
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 15 Vol. 105; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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