1. School of Micro‐Nano Electronics State Key Laboratory of Silicon Materials Zhejiang University Hangzhou 310014 P. R. China
2. School of Electronic Science and Engineering Nanjing University Nanjing 210008 P. R. China
3. Department of Physics Department of Chemistry Centre for Advanced 2D Materials National University of Singapore 2 Science Drive 3 Singapore 119077 Singapore
4. Department of Physics Chungbuk National University Cheongju 28644 South Korea