1. College of Physics and Information Technology, Shaanxi Normal University, Xi’an, Shaanxi 710119, PR China
2. Electronic Engineering Institute, Xi’an University of Posts and Telecommunications, Xi’an, Shaanxi 710121, PR China
3. Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China
4. Nanchang Research Institute, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Nanchang 330200, China