1. Max Planck Institute for Metals Research, Department of New Materials and Biosystems & University of Heidelberg, Department of Biophysical Chemistry, Heisenbergstrasse 3, D-70569 Stuttgart, Germany, Carl Zeiss AG, Technology Center, Carl-Zeiss-Promenade 10, D-07745 Jena, Germany, and Carl Zeiss AG, Technology Center, Carl-Zeiss-Strasse 56, D-73447 Oberkochen, Germany