1. Low Dimensional Materials Research Centre, Department of Physics, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia
2. Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia
3. University Malaya Centre for Ionic Liquids, Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia
4. Department of Physics and Astronomy, University of Sussex, Falmer, Brighton BN1 9RH, U.K.