1. Chongqing Key Laboratory of Interface Physics in Energy Conversion, College of Physics, Chongqing University, Chongqing 401331, P. R. China
2. College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 401331, P. R. China
3. Analytical and Testing Center, Chongqing University, Chongqing 401331, P. R. China