1. Institute of Laser & Opto-Electronics; College of Precision Instruments and Opto-electronics Engineering; Tianjin University; Tianjin 300072 China
2. Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology; School of Science; Tianjin University; Tianjin 300072 China
3. Center of Material Science; National University of Defense Technology; Changsha 410073 China