1. National Local Joint Engineering Laboratory of Carbon Functional Materials; Graduate School at Shenzhen; Tsinghua University; Shenzhen 518055 P. R. China
2. Laboratory of Advanced Materials; School of Materials Science and Engineering; Tsinghua University; Beijing 100084 P. R. China
3. Department of Mechanical and Aerospace Engineering; The Hong Kong University of Science and Technology; Clear Water Bay; Kowloon Hong Kong China