1. Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA.
2. School of Physics and Technology, Center for Nanoscience and Nanotechnology, and Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, Wuhan University, Wuhan 430072, China.
3. School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
4. Departments of Chemistry and Physics and Astronomy, University of Southern California, Los Angeles, CA 90007, USA.
5. Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, No. 5 Zhongguancun South Street, Beijing 100081, China.
6. Advanced Photon Source, Argonne National Laboratory, 9700 Cass Ave., Lemont, IL 60439, USA.