1. State Key Laboratory of Electronic Thin Films and Integrated DevicesUniversity of Electronic Science and Technology of China Chengdu 610054 Sichuan P. R. China
2. Institute of Microelectronics of Chinese Academy of Sciences Beijing 100029 P. R. China
3. School of Applied and Chemical EngineeringXichang College Xichang 615053 P. R. China
4. Tribology Research InstituteState Key Laboratory of Traction PowerSouthwest Jiaotong University Chengdu 610031 Sichuan P. R. China