1. Laboratoire de Matière Condensée d’Electronique et de Traitement du Signal, Department of Physics, Faculty of Science, University of Dschang, Dschang, Cameroon
2. Institute of Surface Chemistry and Catalysis, University of Ulm, Ulm, Germany
3. Laboratoire de Mécanique et de Modélisation des Systèmes Physiques (L2MSP), Department of Physics, Faculty of Science, University of Dschang, Dschang, Cameroon