Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 27: Poster Session I (Methods: Scanning probe techniques; Methods: Atomic and electronic structure; Methods: Molecular simulations and statistical mechanics; Oxides and Insulators: Clean surfaces; Oxides and Insulators: Adsorption; Oxides and Insulators: Epitaxy and growth; Semiconductor substrates: Clean surfaces; Semiconductor substrates: Epitaxy and growth; Semiconductor substrates: Adsorption; Nano- optics of metallic and semiconducting nanostructures; Electronic structure; Methods: Electronic structure theory; Methods: other (experimental); Methods: other (theory); Solutions on surfaces; Epitaxial Graphene; Surface oder interface magnetism; Phase transitions; Time-resolved spectroscopies)

O 27.118: Poster

Dienstag, 24. März 2009, 18:30–21:00, P2

The cooling process on a picosecond timescale: from bulk to monolayer — Anja Hanisch-Blicharski, •Simone Möllenbeck, Tobias Pelka, Paul Schneider, Martin Kammler, Boris Krenzer, and Michael Horn-von Hoegen — Department of Physics and Center for Nanointegration Duisburg-Essen (CeNIDE), Universität Duisburg-Essen, 47048 Duisburg, Germany

We study the cooling rate of heteroepitaxial thin film systems after fs-laser excitation with ps time resolution by means of ultrafast time resolved electron diffraction in a grazing reflection geometry (RHEED). Diffraction patterns taken at different delays between pumping laser pulse and probing electron pulse are converted to the transient film temperature using the Debye-Waller effect. We present results on ultrathin epitaxial Bi(111)- and Pb(111)-films on Si(001) and Si(111) substrates. For a 6 nm thin Bi-film a rapid increase of the surface temperature from 80 K up to 190 K upon laser excitation is followed by a slow exponential decay with a decay constant of τ = 640 ps which is determined by the thermal boundary resistance at the hetero interface between film and substrate. The large increase of the surface temperature is caused by the small absorption length of 15 nm for photons with λ = 800 nm. For Bi-films the cooling rate varies linearly from τ = 290 to τ = 3200 ps with the film thickness which has been varied between 2.5 and 35 nm while a Pb-monolayer within the (√3×√3) reconstruction shows a cooling rate of only 150 ps.