1. School of Materials Science and Engineering, Beihang University, Beijing100191, P. R. China
2. State Key Lab for Mesoscopic Physics and Frontiers Science Center for Nano-Optoelectronics, School of Physics, Peking University, Beijing100871, China
3. State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Weijin Road, CN300072, Tianjin, P. R. China
4. College of Materials and Chemical Engineering, Minjiang University, Fuzhou350108, P. R. China