1. Center of Advanced Lubrication and Seal Materials, Northwestern Polytechnical University, Xi’an 710072, P. R. China
2. State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
3. Qingdao Center of Resource Chemistry and New Materials, Qingdao 266100, China
4. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China