Regensburg 2007 – scientific programme

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O: Fachverband Oberflächenphysik

O 58: Metal Substrates: Adsorption IV

O 58.1: Talk

Thursday, March 29, 2007, 15:45–16:00, H39

On the interaction between etheylene and defect-sites on the Cu(111) surface — Martin Binder, •Olaf Skibbe, and Annemarie Pucci — Kirchhoff-Institut für Physik, Im Neuenheimer Feld 227, D-69120 Heidelberg

It is well-known, that ethylene adsorbed on rough copper surfaces shows a strong chemical enhancement in the surface enhanced Raman scattering (SERS). In former research, these Raman-active vibrational bands also have been detected also with infrared reflection absorption spectroscopy (IRRAS) on cold deposited and hence rough copper films. They were therefore referred to as defect sites (annealable sites). By evaporating small amounts (sub-monolayers) of copper to the cold surface, we could show that the occurence of such Raman-active absorption bands in IRRAS of ethylene on a smooth Cu(111) surface is related to defect sites. Surprisingly, not only the intensity of the Raman-active bands was increasing with the amount of evaporated copper, but an unforeseen strong decrease in intensity of the infrared-active out-of-plane vibration (CH₂ wagging mode) was also detected. In order to understand the morphology of the roughened surface and the nature of the interaction between the copper adatoms and the ethylene molecules, we used high-resolution electron energy loss spectroscopy (HREELS) to examine the vibrational modes of the copper adatoms on the surface and those of the adsorbed ethylene. By doing so, we found that the CH₂ wagging mode of ethylene is still present on the roughened surface. The loss in dipole-activity of this vibration is an unexpected result. We try to give an explanation.