1. College of Chemistry & Chemical Engineering Northeast Petroleum University Daqing 163318 China
2. Department of Chemistry and Biochemistry San Diego State University 5500 Campanile Drive San Diego CA 92182-1030 USA
3. Department of Physics and Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education Institute of Technological Sciences Wuhan University Wuhan 430072 China
4. Department of Materials Science and Engineering University of California, Irvine Irvine CA 92697 USA
5. Department of Physics and Astronomy University of California, Irvine Irvine CA 92697 USA