[1] Natl Res Fdn, iThemba LABS, Mat Res Grp, NANO Sci Labs, Cape Town, South Africa
[2] Univ Cheikh Anta Diop de Dakar, GPSSM, Fac Sci & Tech, Dakar, Senegal
[3] Univ Pretoria, Inst MAt, Dept Phys, ZA-0002 Pretoria, South Africa
[4] Univ Yaounde I, Dept Phys, Yaounde, Cameroon
[5] CRNA, Algiers, Algeria
[6] Obafemi Awolowo Univ, Ctr Energy Res & Dev, Ife, Osun State, Nigeria