1. Department of Materials Science; University of Silesia; 2, Śnieżna St. Sosnowiec 41-200 Poland
2. Institute of Physics; University of Silesia; 4, Uniwersytecka St. Katowice 40-007 Poland
3. Institute of Electron Technology Cracow Division; 39, Zabłocie St. Cracow 30-701 Poland
4. Institute of Physics; Pedagogical University of Cracow; 2, Podchorążych St. Cracow 30-084 Poland