1. School of Electrical and Electronic Engineering; Nanyang Technological University; Singapore 639798 Singapore
2. Beijing National Center for Electron Microscopy; School of Materials Science and Engineering; The State Key Laboratory of New Ceramics and Fine Processing; Laboratory of Advanced Materials (MOE); Tsinghua University; Beijing 100084 People's Republic of China
3. Beijing National Laboratory for Condensed Matter Physics; Institute of Physics, Chinese Academy of Science; Beijing 100190 China
4. Erich Schmid Institute of Materials Science; Austria Academy of Sciences; A-8700 Leoben Austria
5. Institute of Materials Research and Engineering; Agency for Science, Technology and Research (A*STAR); 3 Research Link Singapore 117602 Singapore
6. School of Materials Science and Engineering; Nanyang Technological University; Singapore 639798 Singapore