1. State 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 the Chinese Academy of Sciences, Beijing 100049, China
3. Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701 Republic of Korea
4. Zoological Institute of the University of Kiel, Am Botanischen Garten 1−9, Kiel D-24098, Germany