1. Department of Applied Physics State Key Laboratory of Power Transmission Equipment and System Security and New Technology Chongqing University Chongqing 400044 P. R. China
2. School of Artificial Intelligence Shanghai University Shanghai 200444 P. R. China
3. College of Physics and Electronic Engineering Chongqing Normal University Chongqing 401331 P. R. China
4. Beijing Institute of Nanoenergy and Nanosystems Chinese Academy of Sciences Beijing 100083 P. R. China
5. School of Materials Science and Engineering Georgia Institute of Technology Atlanta GA 30332 USA