1. Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravska cesta 9, 841 04 Bratislava, Slovakia
2. Microelectronics Research Group (MRG), IESL, FORTH, P.O. Box 1385, 71110 Heraklion, Crete, Greece
3. Polymer Institute, Slovak Academy of Sciences, Dúbravska cesta 9, 845 41 Bratislava, Slovakia
4. Faculty of Mathematics, Physics and Informatics, Comenius University in Bratislava, Mlynská dolina, 842 48 Bratislava, Slovakia
5. Microelectronics Research Group (MRG), IESL, FORTH, P.O. Box 1385, 71110 Heraklion, Greece and Department of Physics, University of Crete, 71203 Heraklion, Greece