1. School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 P. R. China
2. Beijing National Laboratory for Molecular Sciences CAS Research/Education Center for Excellence in Molecular Sciences Institute of Chemistry Chinese Academy of Sciences Beijing 100190 P. R. China
3. School of Chemical Sciences University of Chinese Academy of Sciences Beijing 100049 P. R. China
4. State Key Laboratory of Tribology Tsinghua University Beijing 100084 P. R. China