Ezema, Fabian I., Department of Physics and Astronomy, University of Nigeria, Nsukka, Enugu State, Nigeria; Nanosciences African Network (NANOAFNET) iThemba LABS-National Research Foundation, Somerset West, Western Cape Province, South Africa; UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, College of Graduate Studies, University of South Africa (UNISA), Muckleneuk Ridge, Pretoria, South Africa; Africa Centre of Excellence for Sustainable Power and Energy Development (ACE-SPED), University of Nigeria, Nsukka, Nigeria, Nigeria