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O: Fachverband Oberflächenphysik

O 60: Time-Resolved Spectroscopies

O 60.6: Talk

Thursday, March 29, 2007, 17:00–17:15, H42

Femtosecond laser induced diffusion of CO on vicinal Pt(111)-surfaces — •Marco Lawrenz, Krisztina Stépán, Jens Güdde, and Ulrich Höfer — Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität Marburg, D-35032 Marburg, Germany

Femtosecond laser induced surface diffusion of CO from step edges onto terraces of a vicinal Pt(111) surface has been studied at low substrate temperature using optical second harmonic generation (SHG) as a sensitive probe of the step coverage. We have investigated the diffusion rate as a function of laser fluence and delay between two time-delayed excitation pulses in a two-pulse correlation scheme. Compared to our previous studies on the diffusion of atomic oxygen on vicinal Pt(111) [1], we observe a weaker nonlinear dependence of the diffusion rate on laser fluence (∝ F⁶) in a fluence range of F=2–4 mJ/cm². The two-pulse correlation, on the other hand, has a narrower width of only ≈500 fs, which unambiguously show that the excitation mechanism for CO diffusion is also mediated by the substrate electron- rather than the phonon-system. As in the case of oxygen, the narrow two-pulse correlation can be described within the generalized one-dimensional electronic friction model only, if we assume an electron-temperature-dependent friction coefficient.

[1] K. Stépán et al., Phys. Rev. Lett. 94, 236103 (2005)