1. State Key Laboratory for Mechanical Behavior of Materials Xi'an Jiaotong University Xi'an 710049 P. R. China
2. Department of Materials Science Lomonosov Moscow State University Leninskie gory 1 Moscow 119991 Russia
3. Center for Photonics and 2D Materials Moscow Institute of Physics and Technology 9 Institutskiy per. Dolgoprudny Moscow Region 141701 Russia
4. Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences Leninskii prosp. 31 Moscow 119071 Russia
5. Department of Physics Chalmers University of Technology Göteborg SE 412 96 Sweden