1. Institute of Materials Science, Technical University of Darmstadt, 64287 Darmstadt, Germany
2. Faculty of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47057 Duisburg, Germany
3. Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
4. Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52428 Jülich, Germany
5. Institute of Materials Physics, Georg-August-University of Göttingen, 37077 Göttingen, Germany