1. International Center for New-Structured Materials (ICNSM) State Key Laboratory of Silicon Materials School of Materials Science and Engineering Zhejiang University Hangzhou 310027 P. R. China
2. Institute of Condensed Matter Physics Zhejiang Normal University Jinhua 321004 P. R. China
3. State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 P. R. China