1. Nanoscale Materials Science, Empa, Swiss Federal Laboratories for Materials Testing and Research, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
2. IBM Almaden Research Center, 650 Harry Road, San Jose, California-95120, United States
3. Department of Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
4. Department
of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland