1. Department of Materials, University of Oxford, 16 Parks Road, Oxford OX1 3PH, United Kingdom
2. Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, Tang-Jia-Wan, Zhuhai City, Guangdong 519-082, P.R. China
3. JEOL Ltd., 3-1-2 Musashino, Akishima, Tokyo 196-8558, Japan
4. Electron Physical Sciences Imaging Center, Diamond Light Source Ltd., Didcot, Oxfordshire OX11 0DE, United Kingdom
5. Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States