1. Beijing Institute of Nanoenergy and Nanosystems; Chinese Academy of Sciences; Beijing 100083 P. R. China
2. College of Nanoscience and Technology; University of Chinese Academy of Sciences; Beijing 100049 P. R. China
3. Research Center for Bioengineering and Sensing Technology; Beijing Key Laboratory for Bioengineering and Sensing Technology; School of Chemistry and Biological Engineering, and Beijing Municipal Key Laboratory of New Energy Materials and Technologies; University of Science and Technology Beijing; Beijing 100083 China
4. Center for Green Innovation; School of Mathematics and Physics; University of Science and Technology Beijing; Beijing 100083 China
5. School of Material Science and Engineering; Georgia Institute of Technology; Atlanta GA 30332-0245 USA