1. State Key Laboratory of Functional Materials for Informatics Shanghai Institute of Microsystem and Information Technology Chinese Academy of Sciences Shanghai 200050 P. R. China
2. Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of Sciences Beijing 100049 P. R. China
3. Shanghai Key Laboratory of Multidimensional Information Processing School of Communication and Electronic Engineering East China Normal University 500 Dongchuan Road Shanghai 200241 P. R. China
4. Department of Materials Science State Key Laboratory of ASIC and Systems Fudan University Shanghai 200433 P. R. China
5. Department of Physics Department of Materials Science and Engineering and Department of Biomedical Engineering City University of Hong Kong Tat Chee Avenue Kowloon Hong Kong 999077 P. R. China