1. Department
of Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
2. Physics
Institute, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
3. Electron
Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland