1. Department of Physics, University of South Florida, Tampa, Florida 33620, United States
2. Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, 01328 Dresden, Germany
3. Electron Microscopy Group of Materials Science, Ulm University, 89081 Ulm, Germany
4. Department of Applied Physics, Aalto University, P.O. Box 11100, 00076 Aalto, Finland