1 Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore.
2 Department of Physics, National University of Singapore, Singapore, Singapore.
3 School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore.
4 CAMD and Center for Nanostructured Graphene (CNG), Department of Physics, Technical University of Denmark, Kongens Lyngby, Denmark.
5 Institute of High Performance Computing, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore.
6 Department of Electrical and Computer Engineering, Faculty of Engineering, National University of Singapore, Singapore, Singapore.
7 Institute of Physics, Academia Sinica, Taipei, Taiwan.
8 Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore, Singapore. jh-teng@imre.a-star.edu.sg.