1 School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore.
2 School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore.
3 Jiangsu Key Laboratory of Thin Films, School of Physical Science and Technology, Soochow University, Suzhou, China.
4 Facility for Analysis, Characterisation, Testing and Simulation (FACTS), Nanyang Technological University, Singapore, Singapore.
5 Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore.
6 School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore. fanhj@ntu.edu.sg.
7 School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore. jwang@sustech.edu.cn.
8 Department of Physics, Southern University of Science and Technology, Shenzhen, China. jwang@sustech.edu.cn.