1. EMAT, University of Antwerp, Groenenborgerlaan
171, B-2020 Antwerp, Belgium
2. Department of Solid State Physics, School
of Physics, Aristotle University of Thessaloniki, GR-54124, Thessaloniki, Greece
3. Department of Physics, Oakland University, Rochester, Michigan 48309, United States
4. Laboratory of General and Inorganic Chemical
Technology, Department of Chemistry, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece