1. Institute of Physical Chemistry, University of Hamburg, and Center for Applied Nanotechnology,
Grindelallee 117, 20146 Hamburg, Germany, and The Hamburg Center for
Ultrafast Imaging, University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
2. Institut, für Festkörperphysik, Technische Universität Berlin, Hardenbergstrasse
36, 10623, Berlin, Germany