1. Henan Institute of Advanced Technology, Zhengzhou University, Zhengzhou 450052, P. R. China
2. School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450001, P. R. China
3. School of Materials Science and Engineering, Henan University, Kaifeng 475004, P. R. China
4. College of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450052, P. R. China