1. Physics Department, Aristotle University of Thessaloniki, GR 541 24 Thessaloniki, Greece
2. Microelectronics Research Group (MRG), IESL, FORTH, P.O. Box 1385, 71110 Heraklion Crete, Greece and Physics Department, University of Crete, Heraklion Crete, Greece
3. Department of Electronic & Electrical Engineering, University of Sheffield, Sheffield S1 3JD, United Kingdom
4. Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland