1. CAS Key Laboratory of Standardization and Measurement for NanotechnologyCAS Center of Excellence for NanoscienceNational Center for Nanoscience and Technology Beijing 100190 P. R. China
2. State Key Laboratory of Material Processing and Die and Mould TechnologySchool of Materials Science and EngineeringHuazhong University of Science and Technology (HUST) Wuhan 430074 P. R. China
3. Department of Materials Science and EngineeringCollege of EngineeringPeking University Beijing 100871 P. R. China
4. State Key Laboratory of Superlattices and MicrostructuresInstitute of SemiconductorsChinese Academy of Sciences Beijing 100083 China
5. Beijing Academy of Quantum Information Sciences Beijing 100193 China