[1] Univ Kebangsaan Malaysia, Fac Sci & Technol, Sch Appl Phys, Bangi 43600, Selangor, Malaysia
[2] Univ Malaya, Solid State Phys Res Lab, Dept Phys, Kuala Lumpur 50603, Malaysia
[3] Univ Putra Malaysia, Dept Chem, Fac Sci, Upm Serdang 43400, Selangor, Malaysia