Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 52: Time-Resolved Spectroscopy III

O 52.8: Vortrag

Mittwoch, 27. Februar 2008, 17:00–17:15, MA 042

Time-resolved investigation of laser-induced diffusion of CO on terraces of vicinal Pt(111) — •Jens Güdde, Marco Lawrenz, and Ulrich Höfer — Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität Marburg, D-35032 Marburg

We report on a time-domain study of diffusion of CO on a vicinal Pt(111) surface at low substrate temperature induced electronically via substrate electrons excited by femtosecond laser pulses. Diffusion is observed by monitoring the occupation of step sites on vicinal substrates by nonlinear optical second harmonic generation (SHG). Two-pulse correlation experiments were done to study the dynamics of energy flow from the initially excited substrate electrons to the adsorbate degrees of freedom. In contrast to O/Pt(111) [1], CO has a substantially higher binding energy at the step sites than at the terrace sites. For this reason the steps can be employed as traps for adsorbed CO at low temperatures and laser-induced diffusion can be observed by SHG not only from the steps to the terraces but also from terrace to step sites. For terrace diffusion of CO with a barrier of only 0.2 eV our correlation measurements at substrate temperatures of 40 and 60 K indicate a transition from an electronically driven process at low temperatures to a phonon driven process at higher substrate temperatures.
[1] K. Stépán et al., Phys. Rev. Lett. 94, 236103 (2005).