1. Department of Chemistry, Iowa State University, Ames, Iowa 50011, United States
2. Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, United States
3. Ames National Laboratory, US DOE, Iowa State University, Ames, Iowa 50011, United States
4. School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006, China