1. Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China
2. Department of Electrical Engineering and Computer Science University of Tennessee Knoxville TN 37996 USA
3. Department of Materials Science and Engineering College of Engineering Peking University Beijing 100871 China
4. Department of Physics and Astronomy London Centre for Nanotechnology Thomas Young Centre University College London London WC1H 0AJ UK
5. School of physics Peking University Beijing 100871 China
6. Max Planck Institute for Solid State Research 70569 Stuttgart Germany
7. Center for Multidimensional Carbon Materials (CMCM) Institute for Basic Science (IBS) Ulsan 44919 Republic of Korea
8. Department of Chemistry and Department of Engineering Ulsan National Institute of Science and Technology (UNIST) Ulsan 44919 Republic of Korea
9. Department of Chemistry and Biochemistry Texas State University San Marcos TX 78666 USA
10. Center for Nanoscale Materials Argonne National Laboratory Lemont IL 60439 USA
11. Department of Materials Science Fudan University Shanghai 200433 China