1. Institute
of Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
2. Department
of Chemistry and Nebraska Center for Materials and Nanoscience, University of Nebraska—Lincoln, Lincoln, Nebraska 68588, United States
3. Science Institute of University of Iceland, 101 Reykjavík, Iceland
4. Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, People’s Republic of China
5. Department of Applied Physics, Aalto University, 02150 Espoo, Finland