1. Center of Electron Microscopy and State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, People's Republic of China
2. Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA
3. National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
4. Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
5. General Motors Research and Development Center, Warren, Michigan 48090, USA
6. Department of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200240, China