1. Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria
2. Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
3. Institute of Electron Microscopy and Nanoanalysis and Graz Centre for Electron Microscopy, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria