1. School
of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
2. Department
of Applied Physics, Chongqing University, Chongqing 400044, China
3. State Key Laboratory of Silicon Materials, School of Materials Science & Engineering, Cyrus Tang Center for Sensor Materials and Applications, Zhejiang University, Hangzhou 310027, China
4. Beijing
Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences; National Center for Nanoscience and Technology (NCNST), Beijing 100083, China