1. Institut for Electronic, Microelectronic and Nanotechnology, Centre National de la Recherche Scientifique, Villeneuve d'Ascq, France
2. Transport at Nanoscale Interfaces Laboratory, Swiss Federal Laboratories for Materials Science and Technology (EMPA), Dübendorf, Switzerland
3. Swiss Nanoscience Institute, University of Basel, Switzerland
4. Department of Physics, University of Basel, Switzerland