1. Institute of Crystalline Materials; Shanxi University; Taiyuan Shanxi 030006 China
2. College of Electronic Information and Control Engineering; Beijing University of Technology; Beijing 100124 China
3. Department of Chemistry; Rice University; Houston TX 77005 USA
4. Richard E. Smalley Institute for Nanoscale Science and Technology; Rice University; Houston TX 77005 USA
5. Scientific Instrument Center; Shanxi University; Taiyuan Shanxi 030006 China