1. Department of PhysicsCity University of Hong Kong Hong Kong 999077 P. R. China
2. Shenzhen Research InstituteCity University of Hong Kong Shenzhen 518057 P. R. China
3. Herbert Gleiter Institute of NanoscienceNanjing University of Science and Technology Nanjing 210094 P. R. China
4. State Key Laboratory of Silicon MaterialsKey Laboratory of Advanced Materials and Applications for Batteries of Zhejiang Province, and Department of Materials Science and EngineeringZhejiang University Hangzhou 310027 P. R. China