1. School of Materials Science and Engineering; Georgia Institute of Technology; Atlanta GA 30332-0245 USA
2. Marine Engineering College; Dalian Maritime University; Dalian 116026 China
3. School of Physics and Materials Science; Anhui University; Hefei Anhui 230601 China
4. Department of Engineering Mechanics; Zhejiang University; Hangzhou Zhejiang 310027 China
5. Beijing Institute of Nanoenergy and Nanosystems; Chinese Academy of Sciences; Beijing 100085 China