1. Deutsches Elektronen-Synchrotron (DESY), Notkestrasse
85, D-22607 Hamburg, Germany
2. Universität Hamburg, Department Physik, Institut für Experimentalphysik,
Luruper Chaussee 149, D-22761 Hamburg, Germany
3. MPI of Colloids and Interfaces, Department of Biomaterials, Am Mühlenberg
1, D-14476 Potsdam-Golm, Germany