[1] Chiang Mai Univ, Dept Phys & Mat Sci, Fac Sci, Chiang Mai 50200, Thailand
[2] Suranaree Univ Technol, Inst Sci, Sch Phys, Nakhon Ratchasima 30000, Thailand
[3] NANOTECH SUT Ctr Excellence Adv Funct Nanomat, Nakhon Ratchasima 30000, Thailand
[4] Univ Texas San Antonio, Dept Elect & Comp Engn, Coll Engn, San Antonio, TX 78249 USA