1. Group of Electron Microscopy of Materials Science, Central Facility for Electron Microscopy, University of Ulm, 89081 Ulm, Germany
2. COMP Centre of Excellence, Department of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 Aalto, Finland
3. Institute of Theoretical Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
4. Electrical Engineering Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
5. Department of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 Aalto, Finland