1. ENSTA Bretagne, IRDL-UMR CNRS 6027, Brest, F-29200, France;
2. Nanomaterials Laboratory, University of Dayton, Dayton, OH 45469-0168 e-mail:
3. ENSTA Bretagne, IRDL-UMR CNRS 6027, Brest, F-29200, France
4. FSAC-UH2C, Laboratory for Renewable Energy and Dynamic Systems, Casablanca, 20100, Morocco e-mail: