1. Laboratory of Advanced
Materials,
Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
2. Beijing National Center for
Electron Microscopy, Tsinghua University, Beijing 100084, China
3. Center for Advanced Materials
and Nanotechnology, Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania 18015, United
States
4. General Research Institute for Nonferrous Metals, Beijing 100088, China
5. Department of Physics, The University of York, Heslington, York, YO10 5DD,
U.K.