1. Peter Grünberg Institut; Forschungszentrum Jülich; 52425 Jülich Germany
2. Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons; Forschungszentrum Jülich; 52425 Jülich Germany
3. Central Facility for Electron Microscopy; RWTH Aachen University; 52056 Aachen Germany
4. Faculty of Physics; University of Duisburg; 47048 Duisburg Germany
5. Institute of Materials in Electrical Engineering and Information Technology II; RWTH Aachen University; 52056 Aachen Germany