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O: Oberflächenphysik

O 28: Postersitzung (Elektronische Struktur, Grenzfläche fest-flüssig, Halbleiteroberflächen und -grenzflächen, Magnetismus und Symposium SYXM, Methodisches, Nanostrukturen, Oberflächenreaktionen, Teilchen und Cluster, Zeitaufgelöste Spektroskopie)

O 28.73: Poster

Mittwoch, 10. März 2004, 16:00–19:00, Bereich C

Ultrafast energy relaxation and transport effects in photoexcited metals and metallic thin films — •Panagiotis Loukakos, Martin Lisowski, Uwe Bovensiepen, Julia Stähler, Cornelius Gahl, and Martin Wolf — Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin

Time-resolved two-photon-photoemission spectroscopy is used to study the femtosecond dynamics of photoexcited electrons in bulk Ru(001), Cu(111) and thin Cu(111) films epitaxially grown on Si(111)-7x7. After excitation with photon energies of 1.5-2.4 eV the time evolution of the non-equilibrium electron population in the vicinity of the Fermi level is probed by a time-delayed UV pulse. For Cu film thicknesses between 6 nm to 44 nm we find that the electron relaxation rates increase monotonically with film thickness, which is attributed to electron transport out of the probe depth into the bulk. For the electron dynamics at the Ru(001) surface we observe an unexpectedly fast energy dissipation resulting in a decreased temperature at the surface with respect to predictions of the two-temperature model. We attribute this to the influence of the non-thermal electron distribution. With the aid of numerical calculations we propose an increased (ballistic) transport of non-thermalized electrons and a decreased electron-phonon coupling at the surface to account for the efficient energy dissipation into the bulk.