1. Department of Chemistry and Chemical Technologies, University of Calabria, 87036 Rende, Italy
2. CNR-NANOTEC, Istituto di Nanotecnologia, 87036 Rende, Italy
3. Department of Physics, NLHT-Lab, University of Calabria, 87036 Rende, Italy
4. Department of Physics, Case Western Reserve University, 2076 Adelbert Rd., Cleveland, OH 44106, USA