1. College of Railway Transportation, Hunan University of Technology, Zhuzhou 412008, China
2. Qinghai Provincial Key Laboratory of Nanomaterials and Nanotechnology, Qinghai Minzu University, Qinghai 810007, China
3. Hunan Provincial Key Laboratory of Intelligent Sensors and Advanced Sensor Materials, School of Physics and Electronics, Hunan University of Science and Technology, Xiangtan 411201, China
4. School of Physics and Optoelectronics, Xiangtan University, Xiangtan 411105, China