1. State Key
Laboratory of Superhard Materials, Jilin University, Changchun 130012, P. R. China
2. Beijing
Synchrotron Radiation Laboratory, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039, P. R. China
3. Shanghai Synchrotron Radiation Facilities, Shanghai Institute
of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, P. R. China