[1] Univ S Africa UNISA, UNESCO UNISA Africa Chair Nanosci Nanotechnol, Coll Grad Studies, Pretoria, South Africa
[2] Natl Res Fdn, Nanosci African Network, Mat Res Dept, IThemba LABS, Pretoria, South Africa
[3] Univ Western Cape, Dept Phys, ZA-7535 Bellville, South Africa
[4] Tshwane Univ Technol, Dept Phys, ZA-0001 Pretoria, South Africa