1. School of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
2. Chemical Engineering Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
3. Microelectronics Research Group, Department of Physics, University of Crete, P.O. Box 2208, GR 71003 Heraklion, Greece and IESL, FORTH, P.O. Box 1385, GR 71110 Heraklion, Greece
4. Department of Food Technology, Technological Educational Institute of Thessaloniki, 57400 Sindos, Greece