Dresden 2003 – wissenschaftliches Programm
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O: Oberflächenphysik
O 23: Oberfl
ächenreaktionen II
O 23.5: Vortrag
Dienstag, 25. März 2003, 16:00–16:15, M\"UL/ELCH
Electronically induced diffusion of oxygen on a stepped Pt(111) surface — •J. Güdde, K. Stépán, M. Dürr, and U. Höfer — Fachbereich Physik, Philipps-Universität, D-35032 Marburg
We present first experimental results of diffusion of a strongly chemisorbed adsorbate on a metal surface induced by ultrashort laser pulses. We have selected oxygen on stepped Pt(111) as a model system. The dissociative adsorption of O2 at steps on the Pt(111) surface is used to generate a non-equilibrium distribution by decorating the top of the step edges selectively with O [1]. Oxygen diffusion is induced from the step edges onto the terraces at T=77 K by 50-fs, 800-nm laser pulses at a repetition rate of 10 kHz and absorbed fluences of about 20 mJ/cm2. We monitor the coverage at the step edges by exploiting the sensitivity of optical Second Harmonic Generation (SHG) on surface symmetry, which is macroscopically broken by regular steps. The diffusion process can be understood in the same framework as the well studied phenomena of desorption induced by multiple electronic excitation (DIMET). The adsorbate is not directly excited by light, but mediated by laser-excited hot electrons with a distribution that corresponds to an electron temperature of about 2000 K.
[1] P. Gambardella et al. Phys. Rev. Lett. 87, 056103 (2001)