1. Institute of Physics, Rzeszow University, 16A Rejtana St., 35‐310 Rzeszow, Poland
2. Lviv Polytechnic National University, 12 Bandera St., 79013 Lviv, Ukraine
3. Kremenchuk State Polytechnical Institute, 20 Pershotravneva St., 39614 Kremenchuk, Ukraine
4. R & D Institute for Materials SRC “Carat”, 202 Stryjska St., 79031 Lviv, Ukraine