1. National Center for Nanoscience and Technology; Zhongguancun Beijing 100190 P. R. China
2. State Key Laboratory of New Ceramics and Fine Processing; School of Materials Science and Engineering; Tsinghua University; Beijing 100084 P. R. China
3. Center for Nano and Micro Mechanics; Tsinghua University; Beijing 100084 P. R. China
4. Department of Engineering Science and Mechanics; Materials Research Institute; The Pennsylvania State University; University Park PA 16802 USA
5. Key Laboratory of Marine Materials and Related Technologies; Zhejiang Key Laboratory of Marine Materials and Protective Technologies; Ningbo Institute of Materials Technology and Engineering; Chinese Academy of Sciences; Ningbo 315201 P. R. China
6. CAS Center for Excellence in Brain Science and Intelligence Technology; Shanghai 200031 P.R. China