1. Department of Materials Science and Engineering and Department of Biological Applications and Technologies, University of Ioannina, GR-45110 Ioannina, Greece, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL 9747 AG, Groningen, The Netherlands, and Department of Physics, University of Calabria, via P. Bucci, I-87036 Arcavacata di Rende (Cs), Italy