Hamburg 2001 – wissenschaftliches Programm

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O: Oberflächenphysik

O 17: Adsorption an Oberfl
ächen (II)

O 17.4: Vortrag

Dienstag, 27. März 2001, 12:00–12:15, C

Enhanced infrared absorption of SERS active lines of ethylene on Cu films — •M. Sinther¹, P. Lilie², G. Fahsold¹, A. Otto², and A. Pucci¹ — ¹Kirchhoff-Institut für Physik, Universität Heidelberg, Albert-Ueberle-Str. 3-5, D-69120 Heidelberg — ²Institut für Physik der kondensierten Materie, Universität Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf

Vibrational modes of adsorbates on metal films can show surface enhanced Raman scattering (SERS) as well as surface enhanced IR absorption (SEIRA). Both effects are a consequence of field enhancement at the surface of rough films and of a so-called chemical effect. Our experiments show that the chemical effects for SERS and for SEIRA for ethylene on Cu can have the same origin. We investigated ethylene adsorbed on about 5nm Cu on KBr at about 100K with IR transmission spectroscopy. Up to 2L ethylene the spectra show three lines at the positions of the SERS E-lines of the system. The observed IR lines correspond to unusually strong oscillators. Since the background absorption also changes due to adsorption, the interaction of vibrational excitations with electronic excitations at the metal film surface must be relevant to that SEIRA effect. However, ethylene adsorption on Cu surfaces that have been exposed to CO does not lead to observable lines at the SERS positions, i.e., adsorbed CO prevents the dynamical interaction effect for ethylene. This co-adsorption experiment demonstrates that a first layer effect must be responsible for the occurrence of both SERS and SEIRA for a certain vibrational mode.