1. Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, 84104 Bratislava, Slovakia
2. Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University in Bratislava, Mlynska dolina F2, 842 48 Bratislava, Slovakia
3. Institute of Physics, Slovak Academy of Sciences, Dúbravská cesta 9, 84511 Bratislava, Slovakia
4. Centre for Advanced Materials Application, Dúbravká cesta 9, 84511 Bratislava, Slovakia