1. Division
of Physics and Applied Physics, School of Physical and Mathematical
Sciences, Nanyang Technological University, Singapore 637371, Singapore
2. MajuLab, CNRS-UNS-NUS-NTU International Joint Research Unit, UMI 3654, Singapore 639798, Singapore
3. Laboratoire
Pierre Aigrain, Département de physique de l’ENS, Ecole
normale supérieure, PSL Research University, Université
Paris Diderot, Sorbonne Paris Cité, Sorbonne Universités, UPMC Univ.
Paris 06, CNRS, 75005 Paris, France
4. State
Key Laboratory of Surface Physics, Department of Physics, Fudan University, Shanghai 200433, People’s Republic of China
5. NOVITAS,
Nanoelectronics Center of Excellence, School of Electrical and Electronic
Engineering, Nanyang Technological University, Singapore 639798, Singapore