1. Physics of Supramolecular Systems and Surfaces, University of Bielefeld, 33615 Bielefeld, Germany
2. Physikalisch-Technische Bundesanstalt, 38116 Braunschweig, Germany
3. National Center for Electron Microscopy, Berkeley, California 94720, United States
4. Theoretical Physics III, Ruhr-Universität Bochum, 44801 Bochum, Germany
5. Central Facility for Electron Microscopy, RWTH Aachen, 52074 Aachen, Germany