1. Nanotechnology and Advanced Materials Laboratory,
Electrical Engineering Department, Technological-Educational Institute of Western Greece, GR-26334 Patras, Greece
2. Department of Physics, University of Patras, GR-26500 Patras, Greece
3. Department of Chemistry, University of Cyprus, Nicosia 1678, Cyprus
4. Department of Chemistry, University of Hamburg, D-20146 Hamburg, Germany