Regensburg 2002 – wissenschaftliches Programm

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O: Oberflächenphysik

O 30: Methodisches (Experiment und Theorie)

O 30.6: Vortrag

Donnerstag, 14. März 2002, 12:30–12:45, H44

Multi-Photon Photoemission Electron Microscopy — •Gerhard H. Fecher1,2,3, Oliver Schmidt2, Yeukuang Hwu3, and Gerd Schönhense21Westfälische Wilhelms - Universität, Physikalisches Institut, Münster — 2Johannes Gutenberg - Universität, Institut für Physik, Mainz — 3Academia Sinica, Institute of Physics, Taipei, Taiwan

The spatial distribution of multi-photon photoemission yield was imaged utilizing photoemission electron microscopy (PEEM) excited by means of femtosecond laser pulses with a photon energy below the work function threshold. The second order electron yield of the metallic as well as organic films adsorbed on silicon depends strongly on the sample topography and the polarization of the photons. Centers of enhanced high-order yield, so called ’hot spots’, were observed on the surface of various samples. These hot spots were preferentially excited with s-polarized light. The order of nonlinear processes in photoemission was visualized introducing logarithmic scaled images. A mapping of nonlinear effects in photoemission from Pentacene covered silicon exhibited a third order process at rough sample areas being preferentially excited with s-polarized laser radiation. Doping of the Pentacene layers lead to a decrease of the order of the nonlinear photo yield. The decrease was found to be stronger on Pentacene covered areas compared to bare parts of the sample.

(Funded by the NSC of Taiwan: 89-2811-M-001-0002 and the DfG: Fe/444)

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