1. Hunan Key Laboratory of Super Microstructure and Ultrafast Process School of Physics and Electronics Central South University Changsha Hunan 410083 P. R. China
2. Siyuan Laboratory Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Energy Materials Department of Physics Jinan University Guangzhou Guangdong 510632 P. R. China
3. Department of Physics and Astronomy University of Rochester Rochester NY 14627 USA
4. State Key Laboratory of Powder Metallurgy Central South University Changsha Hunan 410083 P. R. China