1. Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
2. Department of Material Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
3. Schlumberger K. K., 2-2-1 Fuchinobe, Sagamihara, Kanagawa 252-0206, Japan
4. Faculty of Engineering
5. Research Center for Exotic Nano Carbon Project
6. Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
7. Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China