1. Lviv Institute of Materials of Scientific Research Company "Carat", Stryjska 202, 79031 Lviv, Ukraine
2. Lviv Polytechnic National University, Bandera 12, 79013 Lviv, Ukraine
3. Institute of Physics of Jan Długosz University of Czestochowa, al. Armii Krajowej 13/15, 42-201 Częstochowa, Poland
4. Fachhochschule Köln/University of Applied Sciences, Betzdorfer 2, 50679 Köln, Germany