Dresden 2011 – scientific programme

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O: Fachverband Oberflächenphysik

O 90: Electronic structure III

O 90.8: Talk

Thursday, March 17, 2011, 19:00–19:15, WIL C107

The role of diffraction in (e,2e) experiments — •Frank O. Schumann, Zheng Wei, Rajendra Dhaka, and Jürgen Kirschner — Max-Planck-Institut für Mikrostrukturphysik, 06120 Halle, Germany

We have performed an electron pair emission study from a Cu(100) surface excited by a primary electron beam covering the energy range 19-100 eV. In the sum energy spectra of coincident pairs we are able to identify distributions from the d states and the sp states. We notice a strong dependence of the relative contribution of these two spectral ranges as a function of the primary energy. The curve describing this behavior resembles the LEED I-V curve of the (0,0) beam. Extending the kinematical picture for the emergence of intensity peaks in LEED to electron pairs predicts intensity maxima in fair agreement with the experimental findings. Further, we studied the pair intensity as a function of the azimuthal orientation of the sample. From simple symmetry considerations we expect a variation of the coincidence intensity. We find an asymmetry up to 20 % when we compare sum energy spectra obtained along two different main symmetry directions. We are able to make contact to selection rules obtained for a (e,2e) process and identify the valence states involved. These results are a critical test of the validity of approximations made in the theoretical description.