[1] Univ Malaya, Fac Sci, Dept Phys, Kuala Lumpur 50603, Malaysia
[2] Univ Putra Malaysia, Fac Sci, Dept Chem, Upm Serdang 43400, Selangor, Malaysia
[3] Univ Putra Malaysia, Inst Adv Technol, Funct Device Lab, Upm Serdang 43400, Selangor, Malaysia
[4] Univ Kebangsaan Malaysia, Sch Appl Phys, Fac Sci & Technol, Bangi 43600, Selangor, Malaysia