[1] Univ Nigeria Nsukka, Dept Phys & Astron, Nsukka, Nigeria
[2] Univ Western Ontario, Dept Phys & Astron, 1151 Richmond St, London, ON N6A 3K7, Canada
[3] IThemba LABS Natl Res Fdn, Nanosci African Network NANOAFNET, 1 Old Faure Rd,Somerset West,7129,POB 722, ZA-7129 Somerset West, Western Cape Pr, South Africa
[4] Univ South Africa UNISA, Coll Grad Studies, Nanosci Nanotechnol, POB 392, Pretoria, South Africa
[5] Pusan Natl Univ, Global Frontier R&D Ctr Hybrid Interface Mat, Busan 46241, South Korea
[6] CSIR, Energy Mat Mat Sci & Mfg, Pretoria, South Africa
[7] Univ Nigeria, Dept Pure & Ind Chem, Nsukka, Enugu, Nigeria