1. Institute of Physics, University of Potsdam, Am Neuen Palais 10, D-14469 Potsdam, Germany; Institute of Ion Beam Physics and Materials Research, Bautzner Landstrasse 128, D-01328 Dresden, Germany; Fraunhofer Institute for Applied Polymer Research, Geiselberg-Str. 69, D-14476 Golm, Germany; Macromolecular Chemistry, University of Wuppertal, Gauss-Str. 20, D-42097 Wuppertal, Germany; and Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany