Affiliation: | 1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371, Singapore;2. Institute of Nanoscience and Nanotechnology, Department of Physics, Huazhong Normal University, Wuhan 430079, P. R. China;3. School of Materials Science and Engineering, Nanyang Technological University, 639798, Singapore;4. Department of Materials Science and Engineering, National University of Singapore, 117576, Singapore |