1. Peter Grünberg Institute; Research Centre Jülich; D-52425 Jülich Germany
2. Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons; Research Centre Jülich; D-52425 Jülich Germany
3. The School of Electronic and Information Engineering; Xi'an Jiaotong University; Xi'an 710049 China
4. II. Physics Institute; University of Cologne; D-50937 Cologne Germany
5. Beijing National Center for Electron Microscopy; Laboratory of Advanced Materials and Department of Materials Science and Engineering; Tsinghua University; Beijing 100084 China
6. Central Facility for Electron Microscopy (GFE); RWTH Aachen University; D-52074 Aachen Germany