1. School of Applied Physics and Materials, Wuyi University, Jiangmen 529020, P. R. China
2. Institute of Applied Physics and Materials Engineering, University of Macau, Macao SAR, 999078, P. R. China
3. International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
4. Department of Physics and Chemistry, Faculty of Science and Technology, University of Macau, Macao SAR, 999078, P. R. China