1 Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Singapore 138634;; Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117575. Electronic address: michel.bosman@gmail.com.
2 Institute f. Electron Microscopy and Nanoanalysis, Graz University of Technology and, Centre f. Electron Microscopy, Graz, Austria. Electronic address: gerald.kothleitner@felmi-zfe.at.