Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 18: Poster Session I - MA 141/144 (Atomic Wires; Size-Selected Clusters; Nanostructures; Metal Substrates: Clean Surfaces+Adsorption of Organic / Bio Molecules+Solid-Liquid Interfaces+Adsorption of O and/or H; Surface or Interface Magnetism; Oxides and Insulators: Clean Surfaces)

O 18.18: Poster

Montag, 25. Februar 2008, 18:30–19:30, Poster F

Probing correlated electron-pair emission from a W(001) surface — •Milton Muñoz-Navia, Carsten Winkler, Michael Birke, Ram Shanker Patel, Frank Oliver Schumann, and Jürgen Kirschner — Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany

An electronic system which is excited by a photon can respond by the simultaneous emission of an electron-pair also called Double Photoemission (DPE). It has been established theoretically that a non-zero DPE intensity requires electron-electron interaction. Besides the simultaneous ejection of two electrons upon photon absorption, another possible pathway of pair emission is that the photon is absorbed by a single electron which scatters from another electron. To study their relative contributions we have analysed the pair emission from a W(001) surface excited by 25 eV and 29.5 eV photons in comparison with 20 eV and 25 eV electrons. The experiments were performed with a coincidence time-of-flight setup with two channelplate detectors in back-reflection geometry. In the (γ,2e) experiments BESSY II synchrotron facility operated in single-bunch mode was used as pulsed light source, while for the (e,2e) experiments, a pulsed electron gun was employed. We find that the 2D-energy distributions for photon absorption or electron excitation are markedly different. Qualitatively this difference can be understood by the selection rule for DPE. Hence, the (γ,2e) intensity has a significant contribution due to the DPE process.