1. School of Physics and Materials Engineering, Dalian Nationalities University, Dalian 116600, People's Republic of China
2. School of Physics, Dalian University of Technology, Dalian 116024, People's Republic of China
3. Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Dalian University of Technology), Ministry of Education, Dalian 116024, People's Republic of China