Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 63: Symposium: Frontiers of Surface Sensitive Electron Microscopy II (Invited Speakers: Jürgen Kirschner, Liviu Chelaru, Michael Bauer, Claus Schneider)
O 63.1: Hauptvortrag (ohne Erstattung)
Donnerstag, 28. Februar 2008, 09:30–10:00, MA 043
Development of a “momentum microscope” for imaging of valence band electron states — •Juergen Kirschner1, Burkhard Kroemker2, and Matthias Escher3 — 1MPI fuer Mikrostrukturphysik, Weinberg 2, 06120 Halle — 2Omicron Nanotechnology GmbH, Taunusstein — 3Focus GmbH, Hünstetten-Hesselsbach
Our aim is to image the momentum distribution of photoexcited valence band electron states in an energy plane through the Brillouin Zone. Our design is based on a modified NanoESCA comprising a Photoelectron Emission Microscope (PEEM) with an imaging energy filter. The basic idea is not to use the real space image from the objective lens but to transfer the momentum image in the focal plane into a hemispherical analyzer by an additional transfer lens. The aberrations of the analyzer are compensated by a second hemisphere such that the inner electron trajectories in the first sphere become the outer trajectories in the second sphere. Thus, an aberration corrected image of the angular distribution of the electrons leaving the sample within a certain area (~ 70 µm diameter) appears at the exit of the second analyzer. The projected image displays the dispersion of the valence electrons within a plane of constant energy. The full valence band can be observed by a sequence of parallel cuts through the Brillouin zone. Because of the parallel detection of all electrons within a given energy window the process is very fast. We demonstrate with a Cu(111) surface and a standard discharge laboratory source (HeI) that complete dispersion planes can be obtained within a couple of minutes.