1. Institute of Radiophysics and Electronics, National Academy of Sciences of Ukraine, Kharkov, Ukraine
2. Polytechnical University of Kharkov, Kharkov, Ukraine
3. Institute of Material Science Problems, National Academy of Sciences of Ukraine, Chernovtsy, Ukraine
4. Institute of Physics, Poznań University of Technology, Piotrowo 3, 60-965 Poznań, Poland