1. School of Materials
Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
2. State
Key Laboratory of Crystal Materials, Shandong University, Jinan, Shandong 250100, P. R. China
3. Department of Materials Science and Technology, University of Crete, 71003 Heraklion, Greece
4. Division of Chemistry and Biological Chemistry, School of Physical
and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore