1. Institute of Physics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 04154 Košice, Slovakia
2. Institute of Manufacturing Management, Faculty of Manufacturing Technologies, Technical University of Košice, Bayerova 1, 080 01 Prešov, Slovakia
3. Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 04001 Košice, Slovakia