1. Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, United States
2. Department of Physics, Wuhan University, Wuhan, Hubei 430072, China
3. Department of Materials Science and Engineering, University of California, Irvine, California 92697, United States
4. Department of Physics and Astronomy, University of California, Irvine Irvine, California 92697, United States