1. Institute
of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
2. Department
of Applied Physics, Waseda University, 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, Japan
3. Department of Applied Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
4. Department
of Physics, National University of Singapore, 2 Science Drive 3, 117551, Singapore
5. Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, 117546, Singapore
6. PRESTO, Japan
Science and Technology Agency, 4-1-8
Honcho, Kawaguchi, Saitama 332-0012, Japan
7. Department
of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore