1. Material Research Division, iThemba LABS, P.O. Box 722, Somerset West, 7129, South Africa
2. School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X54001, Durban, 4001, South Africa.
3. Department of Mathematics, Statistics and Physics, Durban University of Technology, Steve Biko Campus, Durban, 4001, South Africa.