1. Department of Materials Science and Engineering, Faculty of Engineering; National University of Singapore; 10 Kent Ridge Crescent 119260 Singapore
2. Faculty of Science; Universiti Brunei Darussalam; Jalan Tungku Link Gadong BE1410 Brunei Darussalam
3. Laboratory of Photonics and Interfaces, Institute of Chemical Science and Engineering, Faculty of Basic Science; École Polytechnique Fédérale de Lausanne; CH-1015 Lausanne Switzerland