1. College of Physics, Chongqing University, Chongqing 401331, P. R. China
2. College of Materials, Chongqing University, Chongqing 401331, P. R. China
3. Analytical and Testing Center, Chongqing University, Chongqing 401331, P. R. China
4. Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, P. R. China