1. Department
of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
2. Institute
of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory
for Carbon-Based Functional Materials and Devices, Collaborative Innovation
Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215123, People’s Republic of China
3. Institute
of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore 138634, Singapore
4. School
of Engineering and Information Technology, Murdoch University, Murdoch, Western Australia 6150, Australia
5. School
of Physics, University of Wollongong, Wollongong, New South Wales 2552, Australia