1. Department of Physics, University of the Free State, Bloemfontein, South Africa
2. Department of Applied Physics, Chandigarh University, Gharuan, Mohali (Punjab), India
3. Centre for Microscopy, Department of Microbial, Biochemical and Food Biotechnology, University of the Free State, Bloemfontein, South Africa
4. Science and Engineering Research Board, Department of Science & Technology, New Delhi, India