1. Institute of Physics & IMN MacroNano, Ilmenau University of Technology, Ilmenau 98693, Germany
2. Department of Physics, College of Science, University of Al-Mustansiryah, Baghdad, Iraq
3. School of Optical
and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China
4. Central
Facility of Electron Microscopy, Electron Microscopy Group of Materials
Science, University of Ulm, Albert Einstein Allee 11, 89081 Ulm, Germany