1. Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy
of Sciences, Lanzhou 730000, China
2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
3. Institute of Nanoscience and Nanotechnology, School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China
4. School of Mechanical Engineering, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, China