1. Leibniz Institute for Solid State and Materials Research (IFW) Dresden e.V., Helmholtzstraße 20, D-01069 Dresden, Germany
2. Department of Physics, Faculty of Science, Sohag University, 82524 Sohag, Egypt
3. Department of Chemistry, University of Oslo, Postbox 1033, Blindern, N - 0315 Oslo, Norway