1. School of Physical and Mathematical Sciences; Nanyang Technological University; 637371 Singapore Singapore
2. Singapore Institute of Manufacturing Technology; 71 Nanyang Drive 638075 Singapore Singapore
3. Department of Physics and Siyuan Laboratory; Jinan University; Guangzhou 510632 P. R. China
4. School of Electrical and Electronic Engineering; Nanyang Technological University; 50 Nanyang Avenue 639798 Singapore Singapore
5. School of Materials Science and Engineering; Nanyang Technological University; 639798 Singapore