1. Collaborative Innovation Center of Advanced Microstructures National Laboratory of Solid State Microstructures School of Physics Nanjing University 22 Hankou Road Nanjing 210093 P. R. China
2. School of Materials Engineering Jinling Institute of Technology 99 Hongjing Avenue Nanjing 211169 P. R. China
3. College of Engineering and Applied Sciences Nanjing University Nanjing 210093 P. R. China