1. Department of Physics, University of Science and Technology Beijing, Beijing100083, China
2. Fracture and Reliability Research Institute, School of Engineering, Tohoku University, Sendai980-8579, Japan
3. State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
4. State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing100083, China
5. School of Integrated Circuit Science and Engineering, Beihang University, Beijing100191, China