1. School
of Materials Science and Engineering, Beihang University, Beijing 100191, China
2. Department
of Physics, South University of Science and Technology of China, Shenzhen 518055, China
3. Shenzhen Key Laboratory of Thermoelectric Materials, Shenzhen 518055, China
4. Department
of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
5. Department
of Materials Science and Engineering, National University of Singapore, 7 Engineering Drive 1, Singapore 117575, Singapore
6. State Key
Laboratory of Silicon Materials and School of Materials Science and
Engineering, Zhejiang University, Hangzhou 310027, China