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. Department of Microelectronic Science and Engineering School of Physical Science and Technology Ningbo University Ningbo 315211 P. R. China
4. Department of Materials Science 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