1. College of Materials Science and Opto‐Electronic Technology & Key Laboratory of Vacuum PhysicUniversity of Chinese Academy of Sciences Beijing 100049 P. R. China
2. Department of Materials Science and EngineeringUniversity of Science and Technology Beijing Beijing 100083 P. R. China
3. Key Laboratory of Flexible Electronics (KLOFE)Institute of Advanced Materials (IAM)Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM)Nanjing Tech University 30 South Puzhu Road Nanjing 211816 P. R. China
4. Division of PhotonicsCAS Key Laboratory of Standardization and Measurement for NanotechnologyCAS Center of Excellence for NanoscienceNational Center for Nanoscience and Technology Beijing 100190 P. R. China