1. Low Dimensional Materials Research Centre, Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
2. Nanotechnology & Catalysis Research Center, Institute of Graduate Studies, University of Malaya, Level 3, Block A, 50603 Kuala Lumpur, Malaysia
3. Department of Chemistry, Faculty of Science, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia