1. School of Information and Control Engineering; Xi'an University of Architecture and Technology; Xi'an 710055 P. R. China
2. Functional Materials Laboratory (FML); School of Materials & Mineral Resources; Xi'an University of Architecture and Technology; Xi'an 710055 P. R. China
3. School of Microelectronics; Xidian University; Xi'an 710071 P. R. China