1. Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan
2. Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, California 90095, United States
3. National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
4. Center for Advancing Materials Performance from the Nanoscale, State
Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an, China