Dresden 2006 – wissenschaftliches Programm
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O: Oberflächenphysik
O 29: Poster session II (Nanostructures, Magnetism, Particles and clusters, Scanning probe techniques, Time-resolved spectroscopy, Structure and dynamics, Semiconductor surfaces and interfaces, Oxides and insulators, Solid-liquid interfaces)
O 29.57: Poster
Mittwoch, 29. März 2006, 14:30–17:30, P2
Description of femtosecond laser induced diffusion within the electronic friction model — •J. Güdde1, K. Stepan1, A.C. Luntz2, and U. Höfer1 — 1Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, D-35032 Marburg — 2Physics Department, Odense University, 5230 Odense M, Denmark
It has been recently shown that diffusion of atomic oxygen on a Pt(111) surface can be induced by femtosecond laser excitation [1]. The energy flow from the optical excitation to the adsorbate has been modeled in the same way as the well-studied process of desorption induced by femtosecond laser excitation is frequently described. Three coupled temperatures for electrons, substrate ions and the adsorbate are introduced and the electronic coupling between adsorbate and metal surface is represented by an electronic friction coefficient ηe. In this way a fast energy transfer to the adsorbate and a nonlinear dependence of the corresponding rate on laser fluence can be reproduced. We have made different approaches for ηe: Ab initio calculations give the correct order of magnitude for the response time, but cannot reproduce the extremely strong nonlinear fluence dependence of the hopping-rate, which has been observed in the experiment [1]. Satisfactory agreement with the experimental data can be achieved only if a strong dependence of ηe on electron temperature is assumed, which is not supported by the ab initio calculations. We will discuss alternative excitation pathways including an anharmonic coupling between different vibrational modes, which may be responsible for an effective temperature dependence of the electronic friction.
[1] K. Stepan et al. Phys. Rev. Lett. 94, 236103 (2005).