1. State Key Laboratory of Electronic Thin Films and Integrated Devices; University of Electronic Science and Technology of China; Chengdu 610054 PR China
2. Department of Electronic and Electrical Engineering; University College London, Torrington Place; London WC1E 7JE UK
3. Arkansas Institute for Nanoscale Materials Science and Engineering; University of Arkansas; Fayetteville AR 72701 USA
4. MOE Key Laboratory of Laser Life Science & Institute of Laser Life ScienceCollege of Biophotonics; South China Normal University; Guangzhou 510631 PR China
5. College of Electronics and Information; Kwangwoon University; Nowon-gu Seoul 139-701 South Korea