1. Adama Science and Technology University, Department of Applied Physics, P. O. Box 1888, Adama, Ethiopia
2. Energy Centre, Smart Places, Council for Scientific and Industrial Research (CSIR), Pretoria 0001, South Africa
3. Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg 2050, South Africa
4. Addis Ababa University, Department of Physics, P. O. Box: 1176, Addis Ababa, Ethiopia