1. Division of
Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371,
Singapore
2. Laboratoire CRISMAT,
ENSICAEN, CNRS UMR 6508, 6 Boulevard du
Maréchal Juin, 14050 Caen, France
3. EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
4. Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore,
117542, Singapore
5. Laboratory
of New-Structured Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou, 310027, People’s
Republic of China