1. Centre for Ionics, Department of Physics, Faculty of Science, Universiti Malaya, Kuala Lumpur 50603, Malaysia
2. Department of Physics, Faculty of Science, College of Science, University of Hafr Al-Batin, Hafer Al-Batin 39921, Saudi Arabia
3. King Abdullah Institute for Nanotechnology, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
4. Graphene Research Institute and Institute of Nano and Advanced Materials Engineering, Sejong University, Seoul 143-747, Republic of Korea