1. Laboratory of Printable Functional Nanomaterials and Printed Electronics
2. School of Printing and Packaging
3. Wuhan University
4. Wuhan 430072, P. R. China
5. Department of Physics and Materials Science
6. Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education
7. School of Physics and Technology
8. City University of Hong Kong
9. Hong Kong SAR, P. R. China