1. Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
2. Chemical Engineering Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
3. Department of Food Technology, The Alexander Technological Educational Institute of Thessaloniki, 57400 Sindos, Greece
4. Department of Physics, Microelectronics Research Group, University of Crete and IESL, FORTH, 71110 Heraklion, Greece