1. Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States
2. Beijing National Laboratory for Molecular Science, The Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
3. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
4. Air Force Research Laboratory, Wright Patterson Air Force Base, Dayton, Ohio 45433, United States
5. College of Science, Beijing Jiaotong University, Beijing 100044, China