1. Department of Physical Chemistry, University of Geneva, 4, 1211 Geneva, Switzerland
2. Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland
3. Department of Quantum Matter Physics, University of Geneva, 1211 Geneva 4, Switzerland
4. Laboratory of Advanced Technology, University of Geneva, 4, 1211 Geneva, Switzerland