1. Swiss Nanoscience Institute 4056 Basel Switzerland
2. Laboratory for Micro and NanotechnologyPaul Scherrer Institut 5232 Villigen Switzerland
3. Department of ChemistryUniversity of Basel 4056 Basel Switzerland
4. Nanotechnology GroupETH Zürich 8803 Rüschlikon Switzerland
5. BiozentrumUniversity of Basel 4056 Basel Switzerland
6. Institute of PhysicsUniversity of Freiburg 79104 Freiburg Germany