1. Jiangsu Key Laboratory or Carbon-Based, Fuctional Materials & Devices, Institute of Functional Nano and Soft Materials (FUNSOM); Soochow University; 199 Ren'Ai Road Suzhou Jiangsu 215123 P. R. China
2. Department of Mathematics and Physics; Jiangsu University of Science and Technology; Zhenjiang Jiangsu 212003 P. R. China
3. Department of Electronic Engineering; The Chinese University of Hong Kong; New Territories Hong Kong